Challenges and Innovations in Geomechanics

Photo-elasticity used in various engineering fields in the past to investigate the stress distributions and concentrations, and it is the only method to visually observe stresses. However, this technique receives less attention nowadays due to the advances of numerical techniques and computational technology. The author utilized this technique to study the stress variations and distributions by considering typical conditions of slip of faults, discontinuities, slopes, foundations and underground openings in continuum and discontinuum and compared the stress states obtained from elastic finite element method. The authors present the outcomes of photo-elasticity experiments and finite element simulations. The results are compared with each other and their implications are discussed.

We present a comparison between the performances of “Strength Reduction” and “Unloading” techniques in the computational application of the so-called “Material Factor Approach” to the stability assessment of tunnel faces. In this framework, we also propose a new unloading-based safety factor for tunnel stability, as an effective alternative to a commonly used, but faulty, loading-based safety factor.

The dynamic forces subjected on a wind turbine combined with high fatigue loading may result in a foundation failure and potentially reduce the expected service life of the tower. Foundation failures may include excessive tower movements, tilt of a tower, or even loss of contact with the ground. The state-of-the-art practice for foundation monitoring involves use of sensors such as tiltmeters, inclinometers or strain gauges at wind farms to measure displacements or tilts, which can be expensive, complex, and time consuming. The research presented in this paper, explores the feasibility of a novel, low-cost mechanical displacement indicator to continuously monitor tower movement relative to the foundation base. In addition, finite element models were developed to investigate the long-term performance, and potential degradation of the wind-turbine foundation system. Modeling results when combined with field monitoring work would aid in improving the design practices or available standards to predict the service life of a wind-turbine foundation system.

This paper deals with elasto-plastic numerical analyses for predicting the collapses, such as cave-ins, of tunnels and underground caverns. Cave-ins often occur during the excavation of tunnels and caverns, particularly those excavated in weak rocks and in highly jointed rock masses. However, cave-ins cannot be predicted by conventional elasto-plastic numerical analyses even though commercially available computer software is used. This is probably due to the fact that the gravitational force may not be considered properly in the analyses. In the conventional numerical analyses of underground structures, such as tunnels and caverns, the initial stresses caused by the gravitational force are firstly determined by linear elastic analyses. This means that the gravitational force is replaced with the Cauchy stress (surface traction vectors), resulting in no more body force existing in the analyses. This computational procedure may be questionable in elasto-plastic analyses because there is no guarantee that the principle of superposition is valid for nonlinear analyses. In other words, stresses in the plastic zone must always satisfy the yielding criterion. Therefore, the stresses in the plastic zone may become smaller if the strength of the rocks is very low. However, it is obvious that the gravitational force must always be preserved, so that the stresses in the plastic zone cannot become smaller than a certain level of stresses caused by the gravitational force. Therefore, if the stresses in the plastic zone tend to become smaller than the certain level of stresses, the underground structures will collapse due to cave-ins.

The paper presents a procedure for utilization of photographic image data via digital photogrammetry for use in geotechnics. The process of data manipulation in various programs in thoroughly described step-by-step. The motivation of the development is to prepare the final geometrical structure for finite element method software, where numerical modelling of problems such as analysis of stability and deformations can be investigated. Additionally, methodology for applying spatial and temporal evolution of geometry is described. As an example of the procedure, a case study of development of 3D model of internal landfill of open cast coal mine Bílina, Czechia is presented.

In this study, dynamic centrifuge model tests in the 50 g field were conducted to investigate the soil-structure behavior in liquefiable sand during large earthquakes. A miniature model of deep mixing walls (DMWs) was made of soil-cement with an unconfined compressive strength of ~ 4,000 kPa to investigate the behavior/toughness of DMWs after yield and failure, regarding their seismic performance. Numerical simulations were conducted to reproduce the experimental behavior. The simulation code MuDIAN was used with the YT model as a soil constitutive equation. The behavior of the excess pore water pressure ratio, soil, and building acceleration were able to replicate the experimental behavior in general, employing soil parameters determined from the laboratory element experiments.

The existing methods for calculating the settlements of the foundations of buildings are designed for the case of a short-term static loading. These methods are not able to take into account the actual loading regimes of soil bases, including changes in the mechanical characteristics of soils in the previous stages of loading, the manifestation of rheological properties over time, the formation and development of cracks, as well as changes in loading conditions. In this paper, the method of calculating the settlement of foundation bases, taking into account the changes of abovementioned soil parameters and loading conditions was considered. The modified Pasternak model is taken as a basis and changes are made by transforming the diagrams of soil deformation under three-axis long-term loading. The ultimate stresses in the soil are determined based on the design model of the soil under triaxial compression, developed by I. T. Mirsayapov and I. V. Koroleva for regime loadings. The method proposed in this paper was tested on a real reconstructed object. Deformation plots and settlement values obtained as a result of calculations were confirmed by the results of geomonitoring.

The aim of this study is to clarify the mechanical behavior of the joint parts in a steel pipe sheet pile (SPSP) foundation under horizontal loading. The foundation structure of SPSPs is constructed by coupling the joints of each SPSP in the ground with the injection of mortar into the joints. For this purpose, the mechanical behavior of the SPSP foundation should be discussed with a clear understanding of the mechanical behavior of the SPSP joints. In the design criteria under lateral loading, however, only the vertical shearing of the joint parts is considered as critical. Accordingly, the precise understanding of the lateral loading capacity of the SPSP foundation was investigated in this study through model experiments and a reproduction analysis by the 3D finite element method. Simply stated, from the lateral loading tests on the SPSP models and their reproduction analysis by a 3D FEM, it was found that the lateral loading causes vertical shear displacements of the joints of the piles arranged in parallel to the loading direction and almost no displacements of the joints of the piles arranged perpendicularly to the loading direction.

This paper presents the methodology applied for assessing the volume of perturbed soil, caused by a piping phenomenon occurred during the excavation of a cross passage (connecting two tunnels excavated with Variable Density TBMs), through the results of the CPT and CPTu tests. Likewise, the approach was used to estimate the positive effect of consolidation countermeasures. It is interesting to note that other in-situ tests have been performed with the same purpose, but without satisfactory results. The main evidences were provided by CPT and CPTu probes, from which it has been possible to define, the highly damaged and weakened areas. By further refining the analysis (also thanks to a 3D geological model done with Leapfrog©), a larger volume was identified as “stress disturbed”, allowing for the definition of the area requiring treatments. This case study was subsequently implemented in the risk assessment procedure for tunnel projects excavated in similar environments.

This study estimated on the bearing capacity of a footing against eccentric vertical load placed on two types of soil, namely, sandy soil and clayey soil, using the rigid finite element method (RPFEM). For the sandy soil, the study newly introduces an interface element into the footing-soil system to properly evaluate the interaction between the footing and the soil, which greatly affects the failure mechanism of the footing-soil system. For the clayey soil, the study improves the analysis procedure by introducing a zero-tension analysis into the footing-soil system. Two friction conditions of the footing surface were considered which are a perfectly rough and smooth conditions. The effect of the eccentric vertical load on the normal stress distribution at the footing base and the failure envelope in V-M plane is thoroughly investigated. According to the obtained results, it can be seen that changes in the normal stress distribution reflecting to both the eccentricity length and the friction condition were observed. Finally, new equations were proposed to determine the normalized V/Vult and the failure envelopes of both sand and clay.

In the hilly and mountainous region, shallow foundations are commonly constructed near or on the face of sloping ground. Conventional bearing capacity theories, established mainly for the plain ground, are not applicable for estimation of bearing capacity for these foundations and a reduction in the estimated bearing capacity is expected due to lesser passive resistance offered by the disturbed failure zone of the footing influenced by the slope face. Such reduction in the bearing capacity depends on the slope geometry, soil strength parameters, position of the footing and inclination of the applied load. In this regard, limit-analysis based bearing capacity theories often provide conservative results leading to uneconomical design of the sub-structure and a numerical framework can further be employed for this purpose. A detailed finite element investigation has been carried out in the present study to explore the influence of slope angle, setback ratio, i.e. location of the footing from the slope crest and load inclination angle on the bearing capacity of a strip footing resting on sloping ground. In addition, the stability of the slopes under consideration is also assessed for the cases when the footing is positioned on the slope crest which has the maximum possibility of slope failure.

The key factors governing the lateral response of a pile group include the pile-head connection rigidity, the pile-soil relative stiffness, the pile spacing ratio, the pile group size and the pile/soil nonlinear response. Since the earlier experimental observations of the existence of group effects it is commonly assumed that the efficiency of a pile group is less than unity and group effects tend to disappear for spacing ratios larger than 6–7. Despite the availability of advanced computational tools, laterally loaded groups are studied in practice via BNWF approaches and researches about the assessment of the pile group efficiency as a function of the displacement level (i.e. load level) are extremely limited. This paper is aimed at numerically evaluating the influence of displacement level, spacing ratio and pile group size on the lateral efficiency of in-line pile groups in a sandy soil. This will be done by using both a BEM code recently developed by the authors and a more advanced and rigorous commercial code. Presented results may be useful for the design of laterally loaded pile groups in a displacement-based design approach.

Ryukyu limestone formation is considered to be not suitable as a foundation rock for large-scale engineering structures in Okinawa Prefecture. However, when Ryukyu limestone formation is quite thick, it results in non-economical foundation design. The characteristics of Ryukyu limestone with various porosity under static and dynamic conditions are investigated and shear behaviour the interface between piles and Ryukyu limestone are tested using large-scale dynamic shear testing device. Furthermore, some photo-elasticity tests on model piles founded model grounds with and without cavities were subjected to loads to check their deformation and stress responses. The stress distributions and load bearing capacity of piles on Ryukyu Limestone Formation are analysed and their implications in foundation design are discussed.

By looking at nature, modern and sustainable engineering solutions can be developed. For instance, fibrous root systems, have inspired new prototypes of foundations, tiebacks or anchorages. A possible configuration of these innovative shapes is a central shaft branched out with multiple arms. Small-scale experiments have shown how root inspired anchorages can bring benefits in terms of pullout capacity and material efficiency (Mallett et al. 2018a, b). However, the failure mechanism of the pullout of these anchors, is not yet fully understood. This paper contributes to examining this issue by means of numerical simulations conducted via the Material Point Method (MPM). Different geometries have been investigated, such as a 3-branched, a 6-branched and a plate anchor system. Special attention is given to the volume of mobilized soil and the shape of the failure surface generated during the anchor pullout. The numerical results are compared with those of small-scale experimental tests presented in Mallett et al. (2018a, b, 2017).

Cavity contraction problems exist in many engineering practices, such as wellbore engineering, pile drilling, tunnel excavation, etc. The unified strength theory considering the influence of principal stress in different degrees was applied to the unloading problem of cavity excavation. With the unloading factor and contraction coefficient introduced, the normalized similarity solution of cavity unloading-contraction was derived under undrained conditions. Compared with the solution without considering the influence of the intermediate principal stress using Mohr-Coulomb criterion, the concrete effects of different degrees of intermediate principal stresses, cohesion and friction angle on the unloading-contraction relationship are given: the larger the intermediate principal stress influence parameter b, the smaller the cavity unloading-contraction effect, and its essence is that the increase of b introduction of b makes elastoplastic boundary moving towards the cavity wall, delays the appearance of the peripheral peak hoop stress, and helps to reduce the cavity wall plastic zone. Based on the dimensionless unloading contraction similarity solution of cavity, a more reasonable quantitative prediction of the radius variation of cavity at a specified unloading degree can be performed for undrained soil.

In granular soils, stresses are transmitted by chains of contact forces from grain to grain. In this work, the average stresses are obtained based on two simplifying hypotheses: the linearization of the chains, and their association with bands of soil. In this way, the intersection of two conjugate bands gives rise to the definition of the basic element of the granular soil: the rhomboid, whose weight is resolved into two unitary forces of contact, which are added along an associated band to achieve the resultant force acting on the back face of a rigid retaining wall. As the kinematics of a wall rotating about its top requires that the lower grains rotate with respect to the upper grains of the backfill, the contact force against the wall follows a passive direction, whereas the conjugate force remains at the original direction, given by the at rest stress state. Because of the angle of the passive chain is greater than the failure angle, the lateral pressure becomes bilinear, with the maximum value near the top, in agreement with the experimental results of several authors. Hence, the lateral force is similar to that of Coulomb, but the point of application is higher.

During the planning phase of tunneling projects, in particular in urban areas, it is crucial to assess the likely extent of structural damage caused by the tunnel construction in close vicinity to existing surface structures. Tunneling inevitably causes ground movements which in turn may have an impact on deformations and stresses of the above-ground structures. For this reason, a reliable estimate of the soil-structure interactions due to tunnelling-induced settlements is essential. In this contribution, various approaches that differ in precision and complexity are employed to predict the magnitude of expected settlements and the vulnerability of structures with regard to tunneling induced damage. In addition, a three-step damage assessment concept adjustable to the necessary level of detail is suggested. Firstly, ground movements are predicted using analytical or numerical approaches. Secondly, the above-ground structures are idealized by means of surrogate beam-, slab- or 3D-models. Finally, structural damage is assessed according to the computed strain pattern or the tilt of the building. This method enables the evaluation of the potential damage to above ground structures associated with planned tunnel alignment. When developing 3D numerical models, the main focus will be to ensure that the building and the soil-structure interactions are represented with an appropriate level of detail. To this end, this paper aims to provide recommendations for a sufficient level of detail (LOD) of surface structures for the assessment of tunneling induced damage in computational simulations in mechanized tunneling.

The paper focuses on the response of framed structures to tunnel excavation in sand. Standard 3D Finite Element analyses, in which the structural elements are explicitly detailed, as well as simplified equivalent beam models were adopted to simulate the influence of the frame and that of the masonry infills. Both approaches well captured the main soil-structure interaction mechanisms. The presence of stiff masonry infills was found to reduce the angular distortions of the frame bays and, as such, to reduce the tunnelling induced damage. For the first time, insights into the efficiency of two-stage models implementing equivalent Timoshenko beams for framed buildings are given.

Deformations and damage induced in masonry buildings due to nearby tunnel construction activities are influenced by various factors relating to the ground conditions and the structural characteristics of the building and its foundations. The current paper draws on recently completed work at Oxford University, UK on three-dimensional (3D) finite element studies on the influence of the foundation and building characteristics on computed tunnel-induced tensile strains in a masonry building, for an idealised form of the problem. Results are presented on the influence of choices on the constitutive model employed for the masonry and the incorporation of openings (for windows and doors) in the building façade; computed damage metrics are shown to be strongly influenced by these two aspects of the model. It is shown that some of the features of these 3D finite element models can be approximately represented by a simplified model employing an elastic building and a nonlinear Winkler soil-foundation interaction model.

Underground construction activities, such as tunnelling, cause local ground movements to occur. Nearby surface structures interact with the moving ground, potentially leading to building damage. Although it is understood that the severity of building damage is influenced by the façade opening ratio (OpR) and the stiffness of the floors, experimental work in this area is lacking. This paper describes the specification and design of an experimental campaign on brick masonry buildings subjected to vertical base movements. The specimens are half-scale models of walls of two-storey buildings; models with different window arrangements and with/without floor slabs are examined. To design the experimental setup, 3D finite element analyses of the model walls were conducted. Key analysis results, presented in this paper, indicate how the examined structural properties (OpR, building weight, floor stiffness) are expected to influence the patterns of damage in the masonry. The finite element results are also used to design an instrumentation system comprising Fibre Bragg Grating (FBG) sensors and a digital image correlation (DIC) system. Data from the tests will support the formulation and validation of structural models for predicting tunnelling-induced damage in masonry buildings.

The paper presents the field monitoring data and a three-dimensional finite-element analysis aiming at back-analysing the response of a multi-storey framed building affected by the EPB excavation of a 12 m diameter tunnel for the L9 Metro Line. Key aspects of this case study are the excavation section being characterised by mixed face conditions, a curved tunnel axis alignment, a cover-to-diameter ratio between 2.5 and 3, and the skewed building orientation with respect to the tunnel. In particular, the soil profile in the area consists of alluvial and detrital deposits of Quaternary age laying above Miocene siltstone and argillite. These demanding conditions led to poor performance of the large diameter EPB machine near the building, significant ground movements, and cracking of several non-structural elements of the building. Numerical results are discussed in the light of available monitoring measurements.

This paper introduces a simplified method to obtain the three-dimensional soil displacement field caused by tunneling, which is subsequently applied to the analyses of piled foundations nearby. Soil displacements around the tunnel heading are idealized by the spherical contraction model, while the cylindrical contraction model is adopted to simulate the response far away from the heading. The two deformation mechanisms are combined through a shape function, with the parameters determined using a heuristic algorithm and comparisons with numerical analyses. To validate the proposed approach, the displacement fields estimated by the simplified solution and the pile group analyses are compared with three-dimensional finite difference simulations, and favorable comparisons are obtained for ground movements, pile deflections, axial forces and bending moments. The proposed approach is computationally efficient, and the presented work forms the basis which can be further explored to develop design charts for deformation parameters under various tunnel geometries and soil conditions. These may then be used for quick evaluation of the complete displacement field around the tunnel.

In order to improve soil-structure interaction models some new applications have been recently developed which can connect the geotechnical to the structural software by sharing loads and movements through an interface tool. The main value of this tool is to analyze the soil-structure interaction on the fly. This paper presents this coupling methodology by analyzing the foundation of a 120 apartment building 30 m in height and with two basements. The foundation consists of a diaphragm wall jointed by a bottom slab at a depth of 8 m. The main soil layers consist of stiff clays underlain by sand and gravel into a dense clay matrix. The importance of this study is twofold: to analyze if the design of the foundation and the structure of the building are suitable and to verify if this construction affects the subway line situated 6 m adjacent to the diaphragm wall. All these issues were overcame by the use of an advanced soil-structure coupling tool which better mimics the real building foundation interaction as opposed to the use of springs with modulus of subgrade reaction, which leads to more conservative results. Finally, the use of a coupling tool has allowed for the validation of the design.

The city of Rome is upgrading its public transportation network with the construction of the 3rd underground railway line. The Line C of Rome underground crosses the historic city centre with significant interferences with existing monuments and buildings of historic value. As a consequence, protective measures are needed to prevent damage to the most sensitive structures. To test the efficiency of pre-installed barriers in reducing tunnelling effects, a line of bored piles was pre-installed in the stretch between Amba Aradam and San Giovanni stations, close to a well instrumented green-field section. This paper presents the monitoring data from both the green-field section and the section where the barrier was installed and compares the observed behaviour with that computed by finite element back-analyses performed using three approaches to simulate tunnel excavation.

The movements around a deep excavation in urban environment is one of the main design issue to be addressed. Various tools are available and they are categorized in different approaches. The first one, the semi-empirical approach, is based on empirical relations between displacements and simple geometrical parameters such as the depth of the excavation He, or the depth of the bedrock Hb. Generally these methods allow for separate predictions of transversal and longitudinal settlement trough. A second one, the numerical approach, is based on the prediction of the green field subsidence trough by means of FEM or DFM. In this case a 2D simulation of the shaft excavation under plane strain assumption is a typical and nearly routinely design step. The large computational resources available have recently pushed forward the frontier of the simulation capabilities allowing a relatively easy access to large 3D numerical models. In the paper FEM analyses of a deep excavation in an urban environment are presented. The subsoil layering is typical of the Napoli area (Italy) and computed 3D settlement troughs are exposed. The influence of typical buildings in the subsidence area is evaluated and discussed on the basis of the computed results and of fitting functions combining longitudinal and transversal settlement trough.

During the design phase of tunnel constructions in urban areas, advanced finite element models are a convenient tool to predict and reduce the impact of settlement on the surface infrastructure. These models can only deliver realistic results if, on the one hand, the level of detail of the model is high enough and, on the other hand, the model parameters have been well calibrated. Since soils are subjected to large parameter uncertainties, the determination of the model parameters is quite challenging. Therefore, measurement data, which is continuously recorded during tunnel construction, is helpful for calibration. However, at first only assumptions can be made to determine the suitable data for model validation. To make this assumption, a global sensitivity analysis is applied to determine the dominant model parameters. Thereafter, in situ measurements of a residence building that is underpassed by the twin-tunnel excavation of the Milan underground line 5 is used for back analyzes. Finally, suggestions are made on further improvement of numerical model.

In this paper, the main results of a numerical geotechnical analysis of the deep excavation carried out in front of MarmorKirken in Copenhagen are presented and compared with the observed performance. The excavation has a maximum depth of about 35 m; a full top-down construction technique was adopted in order to minimize the effects induced by the excavation works on the monument. Foundation soils are characterized by the presence, starting from a depth of about 13 m, of a limestone formation. The comparison between predicted and observed performance shows that a significant amount (about 50%) of the maximum settlements experienced by the church occurred during the construction stage of the retaining wall panels in front of the church. Numerical analyses got the order of magnitude of displacements, but underpredicted both panel construction and excavation induced settlements of the church, while a better agreement was found for horizontal displacements.

Due to urban tunnelling activities, bridges may be subjected to excavation-induced ground movements that can affect their serviceability. The Tideway Tunnel being constructed in London involves multiple under-crossings of bridges along the River Thames. The monitoring data collected will provide an opportunity for the application and validation of numerical methods for tunnel-bridge interaction. Although field monitoring data are not yet available for publication, the response of the Grosvenor Bridge at Battersea to tunnelling-induced displacements is examined in this work with numerical models. In particular, a simple approach for the preliminary assessment of tunnelling impact on framed structures on shallow foundations is presented; the adopted two-stage finite element model uses integral forms of Mindlin’s solutions to calculate the soil stiffness matrix, while structural members including the piers, arches, deck and spandrel columns are modelled as beam elements in the superstructure stiffness matrix. Preliminary results provide useful insights into the response of arch bridges to tunnelling-induced ground movements at different levels of model complexity.

Deep-excavations cause ground movements and, consequently, the deformations of the pile foundation of adjacent buildings. For deep foundations, the soil-pile-structure problem is influenced by both the greenfield soil movement due to excavation and the complex pile-soil, pile-soil-pile and pile-structure interactions. To estimate the greenfield soil displacements induced by the excavation, the superposition of ground losses relying on the virtual image technique is considered for both unsupported and braced deep excavation. Then, a two-stage continuum-based analysis method is used to evaluate the response of piles group (displacements and internal forces) considering a variety of superstructure configurations (i.e., a rigid cap, a stiff slab, and a stiff beam) or free head. Results will clarify the impact of the diaphragm wall support on both the soil movement and response of piles, quantifying the role of the superstructure stiffness on the foundation response. As shown, the presence of a different superstructure has a significant influence on the bending and axial distress of piles.

This study presented the results of numerical analyses for a ballastless asphalt track. The asphalt layer was modelled as a linear viscoelastic (LVE) solid that was resting on an unbound granular layer (UGL) simulated as a non-linear (stress-state dependent) elastic medium. The mechanical properties of these layers were calibrated from laboratory element tests. For a given structural arrangement, the model was interrogated under a vertical impulse load to assess the sensitivity of selected responses to temperature and to the initial compaction-induced horizontal stresses in the UGL. It was found that horizontal tensile strains at the bottom of the asphalt layer, vertical stresses below the UGL, and vertical surface accelerations were all very sensitive to temperature levels. The vertical surface accelerations were also found to be sensitive to the level of compaction-induced stresses in the UGL. In contrast, the other two responses exhibited a moderate dependency on the lateral stresses. The results from this numerical study provide a better overall understanding of the mechanical behaviour of ballastless asphalt tracks.

Differential settlement, particularly at stiffness transitions such as bridge approaches, is a major issue in the rail industry. It generally leads to increased wear and maintenance as well as speed restrictions. Left unchecked, settlement can cause damage or derailment. In this research, we apply a coupled multibody and finite element approach to predict rail settlement. Wheel-rail contact is governed by a penalty formulation based on Hertzian contact. The track substructure, including rails, fasteners, sleepers, ballast, subballast and subgrade, is input as a linearized model, using modal decomposition to improve efficiency. The contact forces between the wheel and rail are extracted from the multibody simulation, and input into a nonlinear finite element analysis determine the settlement of the soil. An elasto-viscoplastic soil model is introduced to determine the yielding and permanent settlement of the soil during a given pass. The model includes nonlinear pressure-dependent shear strength, compaction or dilation at different mean stresses, rate dependence, and effects of triaxial stress state. Since the yielding is small during a given pass, the linear stiffness of the multibody model will still be relatively accurate. The simulations can be used to help predict settlement and examine mitigation techniques or help optimize maintenance schedules.

A study on the load-deformation behaviour of railway ballast aggregates subjected to cyclic loadings using a combined discrete-continuum modelling approach is presented. Discrete ballast particles are simulated in the DEM and the continuum-based subgrade is simulated by the FDM. Interface elements are generated to transmit contact forces and displacements between the two domains (i.e. discrete and continuum) whereby the DEM exchanges contact forces to the FDM, and then the FDM transfers the displacement back to the DEM. Distributions of contact forces, coordination number, stress contours on the subgrade and corresponding number of broken bonds (representing ballast breakage) are analysed.

The increasing excess pore pressure under rail tracks especially in coastal soft soil regions has been indicated as one of the major reasons causing numerous track issues such as mud pumping. When the excess pore pressure develops to a certain degree, it causes considerable increase in hydraulic gradient associated with hydraulic forces over the soil depth that results in upward migration of fines, i.e., mud pumping followed by severe loss of soil mass and excessive deformation of soil matrix. This issue is simulated in this paper by using the computational fluid dynamics (CFD) coupled with the discrete element method (DEM). Subgrade soil is built in DEM with respect to realistic soil profiles while an increasing hydraulic gradient is generated to model upward fluid flows in CFD. The study indicates soil fluidization develops from localized scale via soil piping to overall scale where all particles become suspended and migrate upwards (i.e., heave formation). The overall fluidization results in a severe degradation in the contact network of soil particles (i.e., soil fabric) and effective stress. The study also shows reasonable predictions of the CFD-DEM coupling on the hydraulic response of subgrade soils.

In this work a small displacement finite element model for the coupled hydro-mechanical analysis of concrete dam foundations is adopted. The hydraulic behaviour is simulated assuming that seepage takes place along channels located at the edges of the triangular interface elements which simulate the various discontinuities. The safety evaluation of the sliding stability of an arch-gravity dam, 83 m high is carried out. The main emphasis is given on the simulation of the drainage system and on the results of sliding stability analysis.

Deep foundations are commonly employed as settlement reducers for earth embankments on soft soil layers. Owing to the presence of piles, both stresses transmitted to the foundation soil and average settlements reduce. Since the piles may be interpreted as a vertical heterogeneity for the system, during the embankment construction and the soil consolidation, differential settlements accumulate at both the base and the top of the embankment. This complex interaction mechanism is severely influenced by the embankment height and by the relative stiffness of the various elements constituting this peculiar geostructure. Nevertheless, the approaches commonly adopted in the current engineering practice and the ones suggested by design codes do not explicitly consider the material deformability and do not allow the embankment settlement estimation.In this paper, the practical application of a new displacement based design approach for earth embankment on piled foundations under drained condition is presented. This model, based on the concept of “plane of equal settlement”, explicitly puts in relationship the embankment height, interpreted as a generalized loading variable, and the settlements at the top of the embankment.

This paper describes a new procedure for the performance-based design of geosynthetic-reinforced earth-retaining walls (GREs) using the pseudo-static approach. In this procedure, the seismic coefficient k is calibrated against given levels of seismic performance, the latter typically expressed in terms of threshold values of the permanent displacements accumulated during the seismic event. An equivalence between the seismic-induced upper-bound displacements and the seismic coefficient k is obtained applying the Newmark’s sliding-block analysis to an updated version of the Italian seismic database, correcting the computed empirical relationships to account for the shape of the internal plastic mechanisms, this involving the strength of the reinforcement levels. For a desired level of seismic performance, the wall is therefore designed to obtain the seismic coefficient related to an internal mechanisms ( $$ k_{\text{c}}^{\text{int}} $$ k c int ) lower than that associated to an external mechanism ( $$ k_{\text{c}}^{\text{ext}} $$ k c ext ), thus promoting the activation of plastic mechanisms which mobilise the strength of the soil-reinforcement system that is assumed to be characterised by an adequate extensional ductility.

Shear keys are placed beneath cantilever retaining walls to inhibit the sliding displacements in the wall thus increasing the demand of shear forces and bending moments in the stem of wall under seismic loading. In practice, design forces in walls are computed using conventional Mononobe-Okabe method which depends only on peak ground acceleration (PGA) of motion which does not represent characteristics of the earthquake motion. Earthquakes of different characteristics scaled to same PGA would ideally result in different internal forces in the system. The primary aim of the current study is to propose load factors accounting for these uncertainties associated with the variation in earthquake characteristics using LRFD technique. In view of this, non-linear FE dynamic analyses have been performed in OpenSees on the model of cantilever retaining walls with shear key and has been validated with experimental observations to obtain measured forces. The idea is to compute load factors by statistically correlating the forces predicted using conventional methodology with those from FE analyses and propose a simplified design methodology to account for the involved uncertainties associated with earthquake loading.

The experimental investigations of seepage force on interfacial bed particles furnish only macroscopic phenomenological characteristics. Microscopic numerical analyses provide effective alternative tools to assess the hydraulic and deformation characteristics of cohesionless granular soils of seepage domain in a coupled fashion. The present study reports the application of a 3-D direct particle–fluid simulation model for seepage force on interfacial bed particles of cohesionless granular soils. The seepage force acting on particles comprising the uppermost layer of cohesionless granular soils bed is studied numerically from the micromechanical aspects without macroscopic assumptions. The particle scale calculations are modeled by a soft sphere model, such as the Discrete Element Method (DEM), and the flow of the pore fluid is directly solved at a smaller scale than the diameter of the soil particles by the Lattice Boltzmann Method (LBM). The interaction between the soil particles and the seepage flow is also considered by coupling these methods. A number of series of analyses until critical hydraulic gradient are accomplished. The result shows that the numerically predicted value for the seepage force coefficient of particles near the surface is reduced regardless of the hydraulic gradient. However, the numerical result is not in good agreement with the experimental result reported in (Martin and Aral 1971).

This paper presents an experimental study on the interfacial characteristics of rammed earth materials stabilized with the combination of cement and alkali-activated fly ash (AAFA), an eco-friendly alternative for cement. Several direct shear tests were conducted to obtain cohesion and friction angle to do so. Moreover, pulse velocity and unconfined compression tests were exploited to assess other physical and mechanical properties of this material. Through the methodology used in this work, it is shown that the replacement of cement with AAFA dramatically improved cohesion, compressive strength, and pulse velocity. However, no general correlation was observed for the friction angle.

Recent failures of upstream-raised tailings storage facilities (TSF) raised concerns on the future use of these dams. While being cost-effective, they entail higher risks than conventional dams, as stability largely relies on the strength of tailings, which are loose and normally consolidated materials that may exhibit strain-softening during undrained loading. Current design practice involves limit equilibrium analyses adopting a fully softened shear strength; while being conservative, this practice neglects the work input required to start the softening process that leads to progressive failure. This paper describes the calibration and application of the NGI-ADPSoft constitutive model to evaluate the potential of static liquefaction of an upstream-raised TSF and provides an indirect measure of resilience. The constitutive model incorporates undrained shear strength anisotropy and a mesh-independent anisotropic post-peak strain softening. The calibration is performed using laboratory testing, including anisotropically-consolidated triaxial compression tests and direct simple shear tests. The peak and residual undrained shear strengths are validated by statistical interpretation of the available CPTu data. It is shown that this numerical exercise is useful to verify the robustness of the TSF design.

During the impoundment process of two super-high arch dams, Jingping and Xiluodu arch dams in China, significant width reduction up to 10–90 mm of the valleys and dams have been observed. It is indicated in this report that the width reductions essentially belong to plastic deformation and the mechanism behind the width reduction is related to the change of effective stress in the dam foundation induced by the impoundment. By comparing the numerical results with the measurements, the width reduction of the Jinping arch dam can be well described by poroplasticity theory as a continuum approach. It is shown that the difference between Biot’s effective stress and the plastic effective stress for yield condition plays a key role in the width reduction. The large width reduction of the Xiluodu arch dam, about 90 mm, cannot be described by the poroplasticity theory and may be related to Hubbert’s effective stress principle as a discontinuous approach.

Swelling of soils and rocks is a phenomenon that is experienced in different geological conditions around the world. The design of tunnels in a saturated swelling ground is a difficult task. Difficulties are generally met for characterisation and testing of swelling soils and rocks and for prediction of the response to tunnel excavation and support loading. This paper is intended to describe the methodology to predict the behaviour of tunnels in swelling ground with an application to a case study. Special triaxial laboratory tests were used to obtain the governing parameters. Numerical analyses were performed to simulate swelling by generating a volumetric strain increment in a given zone of the model based on the volumetric strain measured by laboratory tests.

Openings excavated in rocks with anisotropic strength are often affected by serious instability, related to slip along the weakness planes. The Jaeger criterion, which is a discontinuous approach, is widely used in the mining and oil and gas industry, because is based on well-known rock strength parameters. However, this model cannot capture features related to the stability of openings drilled in some anisotropic rocks with the combined effect of the in situ state of stress. The Hoek & Brown criterion, adapted to anisotropic rocks, is a continuous criterion that can describe the complex behavior of different types of anisotropy exhibited by rock material. Here we interpreted the results of triaxial tests carried out on a shale and we defined the parameters of the Jaeger criterion and the modified Hoek & Brown criterion. We investigated the stability of boreholes drilled in this shale by varying the in situ state of stress and we compared the results of the two criteria. We found that the Hoek & Brown criterion can appropriately describe the behavior of this shale and can predict more accurately the width of the instability of openings excavated in different conditions.

A BP neural network model with 4 × 10 × 2 three-layer is developed to predict the maximum Mises stress and horizontal deformation of circular tunnels subjected to earthquake loadings. The four input common factors F1–F4 are extracted from 12 input parameters which represent the characteristics of tunnel liner, surrounding soil and earthquake characteristics. After training and testing of 70 sets of literature data, three earthquake motions are applied to the tunnel of Guangzhou Metro Line 4 as parametric case study. BP ANN and ABAQUS FEA results are compared and found in general agreement with relative error within 15%. Hence, the method based on BP ANN has a certain guiding significance for practical engineering and provides a new approach for the seismic analysis of tunnels.

Itokazu Abuchiragama is a karstic cave in Ryukyu limestone. It was used as an underground shelter during the Second World War. There is a increasing tendency that ground water is seeping in from ceiling of cave after rainfalls. For the safety of entrants, it was necessary to evaluate the stability of the cave under static and dynamic conditions. This is an integrated study is concerned with the risk management of this cave and the evaluation of the cave was carried out through an empirical, analytic and numerical methods. It is understood that it is necessary to examine in the areas accessible to entrants, in particular, the entrance and exit areas. These areas are investigated in details using numerical analyses utilizing Discrete Finite Element Method (DFEM) with a purpose of checking the counter-measures master plan for rehabilitation.

The authors have been involved with the stability problem of the karstic caves beneath Gushikawa Castle remains in Okinawa Island of Japan using different techniques available in rock mechanics and rock engineering. First, several rock classifications were used for the characterization of rock masses surrounding these karstic caves on the basis of geotechnical investigations. Then, some stability assessments of caves were carried out using empirical and analytical techniques. Numerical analyses showed that filling the cavities would increase the safety of the natural rock structures and it was decided to fill the cavities. Furthermore, a monitoring scheme was undertaken to observe the response of cavities before and after filling operations and to see the effectiveness of cavity filling on the stability of the caves.

The Andra’s (French National Agency for Radioactive Waste Management) Meuse / Haute-Marne Underground Research Laboratory in Bure is currently under extension (4th extension), with the excavation of new galleries having different shapes and support types. The galleries are excavated in the Callovo-Oxfordian (COx) claystone, with a creeping behaviour, at 490 m depth. The continuum rheological model which has been considered (among the available ones) is an elasto-visco-plastic model with the Hoek-Brown failure criterion and the Lemaître creep law. The choice of the rock parameters to be used for the design studies of the 4th extension (aiming to verify the stability of support systems over a service duration of 20 yr) has been based on two sets, defined in previous studies and calibrations. The in-situ measurements, provided by the R&D division of Andra, of three galleries and a shaft, excavated about 10 yr ago, have been back-analysed with these two sets of parameters. The comparison of results led to the choice of the most suitable set of parameters for the design of the new extension galleries.

A squeezing Carboniferous formation was met at a depth of 300 m during the excavation of the Saint-Martin-la-Porte access gallery (SMP2) in France within the Lyon-Turin railway link project. Large, time-dependent and anisotropic deformation was observed around the tunnel wall during and after excavation, and difficulties related to tunneling in squeezing ground have been encountered. An anisotropic visco-elastic plastic constitutive law (Tran- Manh et al. 2015) has been proposed in order to model the ground behavior. This model was validated by field auscultation carried out in SMP2. As a part of the base tunnel, a new survey gallery (SMP4) began to be excavated in the recent years across the same squeezing rock formation at a depth of about 600 m. A yield control support system was adopted in the zones of large deformation, which contains highly deformable concrete elements to stabilize the high convergence (Bonini and Barla 2012). In the present work, the studies of SMP2 are extended to SMP4 by considering the constitutive model developed for SMP2. The innovative excavation and support method is taken into account. Numerical modeling is performed using FLAC3D to analyze the tunnel response. A good agreement can be obtained between the field measurements and the numerical results.

Pre-ground improvement is an auxiliary method for mountain tunnels with shallow overburdens in loose sandy grounds. Although pre-ground improvement provides stabilization to the tunnel face and suppresses the settlement of the ground surface, the seismic behavior of the tunnels is not well understood. Previously, the authors performed dynamic centrifugal model experiments and confirmed the basic seismic behavior of shallow overburden tunnels with pre-ground improvement. However, the experiments did not reproduce the tunnel construction process; in other words, the stress release from the ground due to the tunnel excavation was not considered. In this study, therefore, reproduction analyses of the centrifugal model experiments were performed using a two-dimensional elasto-plastic finite element method, and the applicability of the numerical method was examined. Furthermore, analyses reproducing the stress release from the ground were also conducted using the same numerical method. From the results, it was confirmed that the experiments were simulated accordingly by using the proposed numerical method. Moreover, it was found that, in terms of the seismic behavior of shallow overburden tunnels with pre-ground improvement, the numerical results and the experimental results showed the same tendencies whether or not the stress release from the ground due to the tunnel excavation was considered.

The issue of foundation on slopes is associated with bearing capacity as well as slope stability problems. Several investigations are conducted in the past for assessing the ultimate load-carrying capacity and settlement of isolated shallow footing on or near the slope. Very few researches are conducted to study the mechanism associated with the response of interfering footings near a slope. The present study reports about a numerical investigation conducted to study the response of a 14 m high and 220 kV electrical transmission tower located on the crest created by benching of the hill slope. The foundation of the electric transmission tower comprises four isolated square footings for each of its legs. The stability of slope, and in turn the stability of the transmission tower, was jeopardized due to toe cutting. The present study highlights the influence of different footing typologies on the increment of the bearing capacity and enhancement in the resistance to slope failure. It is established that the factor of safety against slope failure (when subjected to toe cutting) increased by 11.71% for a grid footing formed by interconnecting all the isolated square footings beneath the transmission tower.

The identification of rockfall-affected areas depends on a large number of stochastic variables influencing both triggering and propagation phases. Therefore, rockfall hazard assessment presents huge uncertainties linked to the various scales of analysis. At the small scale (e.g. valley scale), a quick evaluation of rockfall hazard zones is generally required in order to highlight the most critical situations where more detailed analyses should be carried out. The Cone Method (Jaboyedoff and Labiouse 2011), recently implemented in the QPROTO plugin for QGIS, allows to reach this goal with simplified geometrical considerations. In a 3D analysis, the energy line angle $${\varphi }_{p}$$ φ p and the lateral spreading angle α define a cone of propagation whose apex is located in the rockfall source point. The most significant issue in using the plugin is the evaluation of these angles, which must be defined by the users to consider all the rockfall dissipative processes included in the energy line method (Evans and Hungr 1993). In this paper a study concerning the influence of slope properties (forest coverage and slope inclination) and block characteristics (shape and volume) is proposed, in order to provide to the users of the plugin a preliminary dataset of calibrated angles.

Nowadays, most slope stability analyses have been performed without considering the effects of shear band width. To improve the estimations, the shear band width was adequately modeled by introducing an internal characteristic length (lc) within the Cosserat continuum framework, and hence the recently developed second-order cone programming optimized Cosserat continuum finite element method (named CosFEM-SOCP) is employed to investigate the effects of shear band width on slope stability. Based on a homogeneous slope example, it can be recognized that neglecting the shear band width for a slope may lead to overly conservative estimations on the FOS of the slope.

A planar sliding landslide with a finite soil layer is located in Anhui province. Soon after the retaining wall was built, cracks appeared in the wall. It is necessary to obtain the value and distribution of the earth pressure behind the wall. The distribution law of earth pressure behind the wall cannot be obtained by using classical Rankine and Coulomb earth pressure theories directly. Therefore, in this work, three methods were adopted to study the earth pressure of the finite soil layer on the retaining wall. 1. Graphic method. Based on the Coulomb theory of earth pressure, the vertical upward cohesion Ca is added and the earth pressure is obtained according to the force vector polygon. 2. Conversion overloading method. The soil beyond the top of the wall is converted into the overload effect on the soil, and then Rankine theory is used to calculate the earth pressure. 3. Numerical analysis method. Finite element software was used to simulate the slope under natural conditions. Based on this study, it was concluded that the value of the earth pressure calculated by the graphic method is the minimum, whereas that obtained by the overload calculation is the maximum. The distribution of earth pressure obtained by numerical simulation of the limited soil mass first increases, then decreases and then once again increases from the top to the bottom of the retaining wall.

In cold regions, soil slope failures frequently occur due to an increase in the degree of saturation of soil by snowmelt and rainfall infiltration. However, studies related to the coupled effects of snowmelt and rainfall infiltration in cold region are very limited. This paper studies a soil slope failure occured on snowmelt period at a natural cut slope of the expressway in Hokkaido, Japan. According to the disaster investigation report, the slope failure was occured by inflitration of snowmelt, rainfall and overflow water from the drainage ditch. To investigate the cause of the slope failure, reproduction analysis which includes the three-dimensional unsaturated/saturated seepage analysis and slope stability analysis was performed. The numerical simulation considers the effects of snowmelt, rainfall, overflow from drainage ditch and surface grass. It is concluded that the overflow from the drainage ditch had serious effects on this slope failure. Moreover, the numerical simulation approach can reproduce the slope failure caused by infiltration of snowmelt, rainfall and overflow from drainage ditch.

In practice the state of equilibrium of a slope is in general calculated by means of Limit Equilibrium Methods. However, varying stress states, hydraulic conditions and failure mechanisms along a potential shear zone affect the development of shear stress during slope movement. For stiff soil e.g. while shearing a decrease of the shear strength after having reached a peak value can be observed. Due to the named effects, the mobilization of shear strength in the shear zone is not homogeneous and slope stability can be underestimated. The contribution presents an algorithm which couples the evolution of mobilized shear stress with shear displacement or shear strain, respectively, in the shear zone when slope movement is assumed. To illustrate the proposed algorithm a slope with a rigid body failure mechanism on a planar slip surface is considered. For the assumed slope model slope stability is calculated considering soil with and without softening behavior.

Global warming is taking place and there is no doubt that the stability of natural and artificial slopes is influenced by climate change. In this context, the present study intends to show, as more quantitatively as possible, the effects of climate change on slopes stability. The analysis was developed considering a non-static approach suitable for meteorological phenomena which are expected to change in the next years. In the analysis a statistical method was combined with a mechanical one: the forecasts of the intensity growth of heavy precipitation were used, as well as the physical laws for describing the response of groundwater table to these rainfall events and the resulting slopes stability. A case study located in Monchiero (Cn), Italy, was used as a test for the analysis and the forecasts described above.

Rock fall is one of the instability forms of rock slopes. It may resulted in loss of life and property, closing main transportation roads and railways and major economic losses. It is important to estimate the rockfalls and their trajectories in order to protect structures and facilities from rockfall events. This paper presents a study on model experiments and numerical simulations on determining the rockfall travel distances for slopes with different slope angles and to investigate the rockfall hazard problem in Cappadocia (Turkey) and Miyagi Island, Okinawa (Japan). The results from the laboratory tests show that the travel distance of rock falls depend upon slope angle, properties of rock block and also the surface morphology and frictional characteristics besides some dynamic properties such as restitution coefficient. The rockfall hazard is an important issue in Cappadocia (Turkey) and Miyagi Island, Okinawa (Japan) and the rockfalls may be severe problem in both regions.

This paper presents a depth integrated, two-layer SPH new model for debris flows with finite differences meshes associated to nodes to describe pore pressure evolution. The proposed model is applied to describe how the flow evolves when arriving at a grid where pore pressure is made zero.

Numerical techniques like the displacement based finite element method and finite element limit analyses (FELA) are utilized with increased regularity to compute ultimate limit states of slopes. Since FELA is limited to associated plasticity it is suggested to use reduced strength parameters in combination with an associated flow rule in order to model non-associated plasticity (Davis approach). Strength reduction finite element analyses (SRFEA) on the other hand could suffer from numerical instabilities when using a non-associated flow rule. Both issues may be overcome by modifications of the original Davis approach. Previous studies of 2D plane strain considerations (in drained conditions) showed the advantages of the modified Davis procedure for both, displacement based FEA in combination with a strength reduction technique and finite element limit analysis. This paper investigates on the one hand 3D FEA and on the other hand the impact of undrained soil behavior when performing strength reduction finite element analysis. In the first section of the paper, the factors of safety determined by means of drained 2D and 3D SRFEA as well as 2D FELA are compared using different strength reduction techniques. The second part deals with the comparison of undrained and drained SRFEA with focus on the evaluation of the obtained FoS, stress paths, excess pore pressures and volumetric strains.

This paper studies the influence of entrainment on the runout behavior of a documented debris flow, in Hunnedalen (Norway), happened on 2nd June 2016. The steepness of the channel and the availability of sediments along the flow path caused the debris flow to grow from approximately 2000 m3 to approximately 19000 m3. This paper aims to back calculate this event, using a Voellmy rheology implemented in RAMMS:DF and including a debris flow entrainment model. Voellmy rheological parameters (friction coefficient μ and turbulence coefficient ξ) are back-calculated using the default parameters of the entrainment model in RAMMS:DF. The back-calculation aims to replicate available field data such as: the deposit shape and the total entrained volume. It is also shown how the total eroded volume is strongly affected by the choice of μ and ξ. Finally, the entrainment parameters are varied from their default value to understand their influence on entrainment magnitude.

Granular flows are relevant to a variety of engineering applications from risk management of natural phenomena such as landslides and rock avalanches, to flow of pills in the pharmaceutical industry. The granular column collapse is an important experiment to study because of the exhibition of both solid and fluid-like behaviours of granular material. Here we present the continuum simulation of axisymmetric granular column collapse for aspect ratios up to 30 by using two constitutive relations: an elasto-plastic model with Drucker-Prager yield criterion, and the $$\mu \left(I\right)$$ μ I rheological model for dense granular flows. Both models are implemented into a Smoothed Particle Hydrodynamics (SPH) code parallelised for CPU clusters with thousands of cores. While very good agreement with experimental data has been reported for both models for small and intermediate aspect ratios, the large-scale simulations conducted for large aspect ratios show that the Drucker-Prager model tends to over-predict final deposit height, and the (I) model under-predicts it. The differences in flow behaviour and final deposit morphology appear to be largely due to the different volumetric behaviour of the models, as well as the rate independence of the elasto-plastic approach whereas the $$\mu \left(I\right)$$ μ I model is rate dependent.

A 3D discrete element model is used to investigate the axial cyclic response of a small-scale displacement piles installed in Fontainebleau sand. Calibration chamber experimental results from literature are used to validate the pile penetration phase of the DEM model which is then employed to simulate stress controlled vertical cyclic loading. The crushable DEM particle model is calibrated using high pressure element test data for the same sand. The model predicts the experimental stress measurements surrounding the jacked pile in both penetrating and unloaded conditions. The DEM model is used to assess micromechanical features hard to detect using experimental and continuum numerical methods. Grain crushing within the soil is observed to occur only below the cone during pile penetration. The analysis of particle stresses and force chains highlight how arching develops around the shaft. These arching effects create a sort of shield around the shaft causing the radial stresses to be lower. After pile installation is completed, a numerical parametric study of stress controlled cyclic axial loading of the pile is performed. The results show that depending on the magnitude of the cyclic load stable or metastable pile cyclic response is attained. The cyclic load amplitude also influences in different ways both stress and density profiles around the pile. These results may serve as a step forward to the understanding of installation effects on axial cyclic performance of jacked piles in sand.

The well-established cavity expansion theory has already been applied to numerous practical problems in geotechnical engineering. Analytical solutions taking into account advanced constitutive soil models, such as the available solutions for drained and undrained cavity expansion using the unified state parameter model for clay and sand (CASM), represent also valuable reference solutions for the validation of numerical models. In this work, the code G-PFEM is used for the fully-coupled analysis of cavity expansion problems at large strains, in order to validate the performance of the numerical model with the implemented CASM under drained and undrained conditions and to investigate cavity expansion under the influence of partial drainage. It is shown that the numerical results compare well with the analytical solutions. Furthermore, the effect of partial drainage where consolidation takes place during the cavity expansion process is highlighted.

This work presents a robust and mesh-independent implementation of an elasto-plastic constitutive model at large strains, appropriate for structured soils, into a Particle Finite Element code specially developed for geotechnical simulations. The constitutive response of structured soils is characterized by softening and, thus, leading to strain localization. Strain localization poses two numerical challenges: mesh dependence of the solution and computability of the solution. The former is mitigated by employing a non-local integral type regularization whereas an Implicit-Explicit integration scheme is used to enhance the computability. The good performance of these techniques is highlighted in the simulation of the cone penetration test in undrained conditions.

The tip resistance measured within the cone penetration test (CPT) can be used to predict the pile tip resistance under axial loading, due to the geometric similarity. Most of the existing correlations were established in terms of siliceous sands, while the data for calcareous sands are limited. Calcareous sands in situ are featured with higher peak internal friction angle, but the strength reduction may be significant due to particle breakage. In this paper, a large deformation finite element approach, the Abaqus finite element package utilizing the Arbitrary Lagrangian Eulerian method (ALE) is used to study cone penetration in calcareous sands. A constitutive model proposed by Yin et al. (2016) and Wu et al. (2017) is incorporated into ALE to describe calcareous sands. The CPT in silicon sands is replicated by a modified Mohr-Coulomb model as well for comparison purpose. Frequent mesh generations are conducted in ALE, to avoid distortion of soil elements around the cone tip.The numerical results of cone tip resistance agree reasonably well with the existing data from centrifuge tests. It demonstrates that the modified Mohr-Coulomb and SIMSAND-Br models have potential to capture the behaviors of silica and calcareous sands. The cone resistance in calcareous sands is found to be affected remarkably by particle breakage around the cone.

Compound mesh panels are structures in which two different nets geometries are employed: a main mesh that provides the bearing capacity and a weaker mesh with a thin sieve size to catch smaller blocks that can pass through otherwise. Typically, only the effect of the main mesh is investigated, and the weaker mesh is considered to provide negligible structural resistance. In this paper, after a calibration procedure, numerical simulations of quasi-static punch tests and a dynamic block impact on a composite double-twist and strand rope mesh are performed. The results show that, under dynamic conditions, the presence of the finer mesh lowers the peak force acting on the main mesh. This effect is not found under quasi-static conditions and has important repercussions on the overall structural resistance as the energy dissipation mechanism reduces the stress on the mesh fence posts.

In this paper a novel node-based explicit smoothed particle finite element method (SPFEM), is utilized to evaluate the progressive slope failure mechanisms. In the SPFEM approach, a node integration method (strain smoothing technique) is introduced into the framework of the particle finite element method (PFEM). The main advantage of SPFEM in slope stability analysis lies in its capabilities to consider the whole dynamic failure process of slope and to simulate large deformation and post-failure of soils. The progressive failure behaviour of a long clayey slope is modelled using SPFEM in conjunction with a strain-softening Tresca constitutive model. The retrogressive failure behaviour of a long clayey slope is analyzed.

Loading and excavation are fundamentally dynamic processes. However, the dynamic effects are often neglected if the overall system is stable following the transient stage. However, there are some cases such that the dynamic processes may result in some damaging effects, which may not be expected from static solutions. In this study, the author consider some typical loading and excavation situations as dynamic problem and evaluate the dynamic variations of strain and stress and compare the results with static solutions. The computed results clearly show that strain and stress states may be much higher than those from static solutions and they may have important implications in practice.

Non-linear dynamic analyses represent a useful tool for the assessment of the seismic response of geotechnical systems. This kind of analyses requires the selection of strong motion records which reflects the seismic hazard at the site of interest. In this regard, international seismic codes prescribe the satisfaction of some compatibility criteria between the selected records and a target elastic response spectrum, in a specific interval of vibration periods, with reference to structural features. However indication for the choose of an appropriate range of vibration periods for geotechnical systems is lacking in current design codes. A procedure for the selection of strong motion records with indications on interval of vibration periods to be considered for geotechnical problems, was recently proposed by the author and co-workers. This paper highlights how the non-linear behaviour of the soil deposit, represents only the starting point of an iterative process useful for fully non-linear dynamic analysis. Specifically, an application of the novel procedure shows how it’s possible to exploit the new selection method as an immediate and simple tool for the selection of input motions for 1-D Equivalent Linear and Non-Linear seismic site response analysis.

The hysteretic damping approach is a satisfactory model for granular soils, although some mathematical inconsistencies may be pointed in its formulation. When cohesive saturated soils or soils saturated with high viscosity fluids are subject to dynamic loads, then a second mechanism of energy dissipation may occur with frequency dependence. The aim of this study is to investigate an alternative method to analyze the phenomenon of damping in soils by looking at the vibration problem as a coupled poromechanical system where the relative displacements and velocities between the fluid and solid phases generate interaction forces that can play an important role in the energy loss. The results predicted by the analytical equation are compared to those obtained from laboratory tests, as well as from other damping models available in the literature, in order to check the validity of the present proposition.

Damages such as settlement and tilting of detached houses due to ground liquefaction have often been observed during recent earthquakes. Ground surveys are necessary to predict the damage due to ground liquefaction. In this study, we focused on the surface wave exploration and passive liner array, which are ones of the geophysical survey methods. The surface wave exploration can tell us the ground information over the wide range. The latter one can give the information from the ground surface down to the deep part. These survey techniques can give us the ground conditions more accurately, more extensively and more quickly than the conventional ones. First, we conducted these surveys in Christchurch, New Zealand damaged by the 2011 Christchurch earthquake. The risk of liquefaction was then evaluated based on surveyed results. The evaluation method using the FL and PL values was used for judging the liquefaction risk. As a result, it was confirmed that the observed damage distribution almost coincided with the high risk area calculated by the shear wave velocity structure.

Many landslides occurred around epicentral region and a large debris avalanche occurred on southern slope of Mt. Ontake and travelled about 12 km down due to the 1984 Western Nagano Prefecture Earthquake (Mw = 6.2). Furthermore, many displaced boulders were observed at the mountaintop and ridge near hypocenter. The horizontal and vertical accelerations near hypocenter were estimated to be more than 2G from these dislocated boulders. However there is no near-field strong motion records and the mechanism of the dislocation has not been clarified in detail so far. Therefore, the authors performed the fault rupture simulations considering the dynamic rupture process of the fault plane to estimate the strong motion around hypocentral region. It is shown that large acceleration occurred in the ridge as a result of amplification of the topography if the critical slip displacement Dc and topography were taken into account in 3D FEM mesh. However, the strong motions near the landslide at Mt. Ontake was not high, which was probably due to large FEM mesh size and no consideration of the decrease of shear wave velocity (Vs) in surface layer.

Analytical method is applied to investigate the influence of material parameters and thickness of vibration isolation barriers on its efficiency. Jet-grouted columns of lightweight and soft geomaterials are shown to be the most effective. The fact is confirmed by 2D modelling with finite element method.

Block-type quay walls are susceptible to seismic damage due to their lack of shear connection between blocks, especially when constructed in liquefiable soil. This study investigates the seismic performance of a block-type quay wall constructed with liquefiable backfill by combining model test, design code-based evaluation, and numerical simulation. A dynamic centrifuge test is conducted to obtain the basic physical seismic response. Results showed that under strong earthquake motion, the quay wall may undergo large lateral deformation and damage due to the liquefaction of the backfill. The same quay wall is then evaluated based on seismic design codes for port structures from the USA, China and Permanent International Association of Navigation Congresses (PIANC), which are shown to be inadequate in predicting the seismic damage. In parallel, high-fidelity numerical modeling utilizing a unified plasticity model for large post-liquefaction shear deformation of sand is performed for detailed seismic response analysis of the quay wall. The numerical analysis can provide a good simulation of the seismic behavior of the block-type quay wall, especially in reflecting the relative displacement between blocks and the liquefaction of the backfill accurately. These comparisons highlight the important role of numerical modeling with high-fidelity constitutive models in the seismic design and analysis of the quay walls with liquefiable backfill.

Non-destructive testing (NDT) plays an important role in material inspection and characterization. In geotechnical engineering, the popular seismic NDT includes Spectral Analysis of Surface Wave (SASW), Multichannel Analysis of Surface Waves Method (MASW) and Continuous Surface Wave (CSW). A forward solver and a back-calculation algorithm are required to determine the soil stratigraphy and the properties of each soil layer. However, most of available forward solvers are limited to elastodynamic solutions in which the soil’s porous nature and water content and can’t be taken into consideration. In this paper, a poro-elastodynamic forward solver for seismic NDT is presented. The proposed solver provides an analytical solution for wave propagation in saturated soil media using the spectral element method. The P and S waves are decoupled through the Helmholtz decomposition. The P waves in solid skeleton and porewater are further decoupled through an Eigen decomposition technique. Such a solver can effectively determine the dispersion relation for a given structure, which can be further used for geophysical inversion application based on surface wave tests.

Global response of bridges is dictated by soil-structure interaction considerations of the entire bridge-ground system. In this study the three-dimensional (3D) longitudinal response of such a bridge-ground system is numerically investigated. A realistic multi-layer soil profile is considered with interbedded liquefiable/non-liquefiable strata. Effect of the resulting liquefaction-induced ground deformation on the bridge-ground system is explored. The analysis techniques as well as the derived insights are of significance for general bridge-system configurations under liquefaction-induced ground deformation.

This paper presents the interaction mechanism of a 12-story building sitting on a piled raft foundation with a strike-slip fault rupture. The mechanical response of foundation including both structural and geotechnical response of the foundation are evaluated through three-dimensional numerical modelling using ABAQUS. The obtained results showed that the raft significantly suffers from rotation about the vertical axpipelinis and horizontal displacement. Both bending moment and shear forces in piles due to fault rupture exceeded the capacity values of piles. The maximum bending moment and shear forces within piles took place at the connection of piles to the raft and exceeded allowable values when the fault slipped more than 0.3 m.

Modeling seismic waves and vibrations propagating into geological structures has always been a challenge since large scale models as well as detailed basin geometry and soil layering are both needed. The optimal accuracy to model the propagation process depends on the frequency range but also on the excitation level.Various numerical methods have been significantly improved along the years to achieve accurate and cost-effective strategies: FDM, FEM, FVM, SEM, BEM, DGM. The first key issue deals with numerical dispersion (link between wavelength and propagation features). Numerical damping may also be a (controllable) issue.Another important question is related to spurious reflected waves at the model boundaries. To reduce such errors, absorbing boundary conditions or absorbing layer methods (PML, CALM, ALID) have gained interest in the recent years.To model seismic waves propagating from the fault to the structure, a coupling strategy (DRM, FEM/BEM, strong vs weak) may be optimized to accurately model the wave radiation at infinity or accommodate large velocity contrast (i.e. large mesh refinement discrepancies).Future research challenges are also discussed: physics based fault rupture, nonlinear soil/rock behavior and characterization, loading history, pore fluids, uncertainties vs spatial variability, interaction with various structures at different scales.

This paper presents a novel numerical-analytical method for dynamics of piles embedded in non-homogeneous transversely isotropic soils. In the method proposed, the piles are modelled using beam-column elements, while a new type of elements called radiation discs are defined at the nodal points of the elements to simulate the wave propagation through the non-homogeneous soil medium. By using radiation discs, the discretisation is only required along the length of piles, while discretisation of surrounding medium, top free surface boundary, and cross sections of piles are avoided. Numerical results are presented and the effect of soil non-homogeneity on lateral compliances of piles and pile groups is particularly emphasised.

In this paper, the seismic performance of a piled raft foundation combined with grid-form deep mixing walls under a strong earthquake is investigated numerically. A 12-story building on the soft clay ground was modeled using a three-dimensional finite element soil–structure interaction model. The model was calibrated using the seismic observation records of a middle-scale earthquake at the building site in the previous study. The elasto–plastic model used for the stabilized soil has the tensile criteria and the shear criteria, and the model has an ability to evaluate the post-peak softening. The analysis result indicates that the induced stress reaches the tensile strength in some parts of the deep mixing walls. However, few parts of them lose large amount of tensile strength as a result of post-peak softening. And the grid-form deep mixing walls are found to keep their function of reducing the bending moment of the piles to an acceptable level.

The behavior under seismic condition of embedded retaining structures is quite complex. When the geometry (prop levels) prevents the formation of kinematic mechanisms and the structural elements do not achieve yield strength conditions, permanent displacements are expected to be relatively low and, therefore, seismic actions may cause significant increases of the forces acting on the structures: these forces are dependent on a number of factors such as the characteristics of the ground motion, the problem geometry, the mechanical behavior of the soil and the soil-structure relative stiffness. In the present study, the results of several dynamic numerical analyses of a multi-propped retaining wall in a dry coarse soil are presented and discussed. The results of the analyses indicate that large structural stresses (bending moments in walls and axial loads on props) develop as consequence of seismic actions. Post seismic stresses remain significantly large as compared to the static condition. The maximum ground acceleration in the free-field seems not to be an effective parameter in order to evaluate the seismic performance of this kind of retaining structures.

In recent years, seismic wave propagation analyses have become a powerful tool to evaluate the site effects in a given region. Among several approaches, the Spectral Element Method (SEM) has been widely used with that purpose because of its flexibility and computational efficiency. The multiple interactions between the soil and structures, denominated site-city effects (SCI), can play a crucial role in densely populated areas. There are many options to model this kind of interaction, especially if the buildings are partially embedded on the soil. This paper evaluates the importance of the proper SCI modeling against more standard uncoupled approaches, focusing on the local interaction between the soil and a group of buildings including inelastic soil behavior. We focus our work on the case of downtown Viña del Mar, a touristic coastal city of central Chile, where the observation of a reiterated distribution of damage in reinforced concrete buildings during two major earthquakes has motivated numerous studies. For that purpose, a realistic 3D numerical model of the area is created, considering the existing buildings. In general, the results indicate that the inclusion of the SCI reduces the maximum interstory drift in most cases, and that the SCI modeling needs to considerate the level of embedment to obtain more precise results.

Consideration of inherent anisotropy is crucial to gaining an improved understanding of the behavior of granular materials. One of the authors examined inherent anisotropy’s effect on the seismic behavior of ground through dynamic centrifuge model tests and revealed that a sandy level ground deposited at a higher angle is more susceptible to liquefaction. In the present paper, seismic response analyses are performed on the liquefiable sandy ground considering inherent anisotropy and their results are compared with the experiment. For modeling the sandy ground, a strain space multiple mechanism model is used; the model has been expanded for describing sand behavior associated with inherent anisotropy, by introducing three anisotropic parameters (a1, a2, and θo). The seismic response analyses with no consideration for permeability anisotropy show that it is difficult to accurately simulate the deposition angle dependency in the experiment, even though the additional anisotropic parameters are employed. This study demonstrates that considering anisotropic permeability, which may depend on the deposition angle, is required as well as the additional three parameters for properly capturing the liquefaction behavior of sandy ground associated with inherent anisotropy.

The catastrophic effects of earthquakes that frequently hit the West coast of South America has motivated this research. The country of Ecuador, situated on the subduction border of the South American and Nazca tectonic plates, has a high seismic exposure. Since the Mw = 7.8 earthquake that occurred on April 16th, 2016, the assessment of stability conditions of dams has become a high priority for the Ecuadorian government. The concrete faced rockfill dam (CFRD) of Mazar, an essential structure for the country, is classified as a large dam by the International Commission on Large Dams (ICOLD). In this research, the numerical seismic analysis of Mazar dam was carried out, including the generation of artificial earthquakes based on acceleration spectra established by Ecuadorian standards. Other aspects related to the dam behavior were also investigated, such as the static and pseudo static stability conditions and the maximum permanent displacements determined by simplified methods. An important conclusion from the 2D numerical analysis is the influence of topographic amplification, which is not taken into account when simplified methods based on 1D wave propagation are used.

A new model, named SANISAND-MSf, is presented that is an extension of the two-surface constitutive model within the framework of bounding surface plasticity. It addresses the modeling of sand behavior under undrained cyclic loading by successful simulation of stress-strain curves, undrained stress paths and strength curves, for various cyclic stress ratios and loading conditions, at both pre- and post-liquefaction stages separately, as opposed to overall simulations of past efforts. The model incorporates a new form of a memory surface for the pre-liquefaction stage and the concept of semifluidized state for the post-liquefaction stage; both address the proper modification of stiffness and dilatancy. The formulation avoids common shortcomings of previous models related to stiffness degradation and singular analytical eventualities. The SANISAND-MSf maintains the well-known ability of the two-surface bounding surface model to simulate successfully monotonic loading at various pressures and densities with one set of model constants and be critical state compatible. This paper addresses the novel capabilities of the proposed model in capturing the challenging aspects of modeling seismic site response analysis of a soil deposit in both pre- and post-liquefaction state of response. The developed modeling framework will contribute to future applications in a realistic and thorough seismic site response analysis.

Severe damages such as large settlement and tilting of detached houses have been often observed due to ground liquefaction in the Great East Japan Earthquake. Liquefaction countermeasures were not adopted for the detached houses since the house owner couldn’t understand the potential of the liquefaction damage. In order to adopt countermeasures for detached houses, the appropriate prediction of the damage is necessary. In this study, SPH simulations with different material parameters such as FL and Fc were carried out targeted for 1-g shaking table tests to understand the effect of ground parameters on housing settlement prediction.

This article proposes an algorithm and its implementation to automatically generate the packing of circles of different diameters in each triangle of a triangular arrangement that covers a closed polygon in R2. The generation is recursive at various levels of depth given different diameters, with the model tending to be self-similar for small particles and more divergent for large particles. This closed polygon can represent the geometric frame for a slope in R2. The algorithm and its implementation are associated with application software called packcircles4bims, which is written in Python and is presented to the community as open and free software.

Heterogeneous rock bodies composed of strong rock blocks surrounded by a weaker finer-grained matrix are often referred to as “BIMrocks” (Block-In-Matrix rocks). These complex formations present a high spatial, dimensional and lithological variability, which makes their characterization an extremely challenging task. As a consequence, geopracticioners have often planned engineering works in bimrocks ignoring the presence of the stronger rock inclusions. However, it is essential that blocks be considered in the analyses in order to obtain reliable results. In fact, rock inclusions strongly affects the strength, deformability and failure surfaces of these geomaterials.In this paper 3D stability analyses are performed with the FLAC 3D code on slope models with variable Volumetric Block Proportions (VBP) to investigate the influence of the rock inclusions on their stability. In order to take the inherent variability of bimrocks into account, a Matlab code was implemented to generate spherical blocks of variable dimensions and locate them randomly within the slope models. Moreover, the stability of a matrix-only slope model is also analyzed by way of comparison. Finally, the paper compares and comments on the results of 2D numerical simulations previously carried out by the author for the same complex block-in-matrix formation.

When dealing with structurally complex formations, the definition of a reliable geotechnical model is often made difficult by the scarcity of undisturbed samples and by the erratic properties of the material. This is particularly true when the original formation suffered strong mechanical stress-strain (i.e. fault zones) and physic-chemical alteration. In this paper, the attempts made to understand the mechanical behavior of a gap-graded heterogeneous soil, named Highly Tectonized Phyllite (HTP), will be presented. To investigate this particular soil whose stress-strain response clearly depends on the grading, an experimental study was performed through triaxial tests mainly on reconstituted samples varying the composition of the mixture.

The preparation of undisturbed representative samples for testing is almost impossible for geological masses such as jointed rock masses, rock accumulations and block-in-matrix-rocks (bimrocks). In this regard the work of Lindquist (1994) on the strength evaluations (and of Medley (1994) on characterization) of bimrocks are now regarded as pioneering research. Subsequent literature confirms the fundamental outcome of Lindquist’s work that when the volumetric block proportion (VBP) in a bimrock increases, the internal friction angle increases and the cohesion decreases. Further: the strength of blocks does not influence overall strength of bimrock – instead due to the strength contrast between strong blocks and weak matrix, the blocks force failure surfaces to pass tortuously around the blocks. More recent work (Sonmez et al. 2018) emphasized that under sufficient normal or confining stress conditions, the failure surfaces may also penetrate into the blocks for block-rich bimrocks with block to block contacts. Therefore, non-linear shear strength envelopes may be expected for especially block-rich bim materials such as rock accumulation (or rockfill) and jointed rock masses. In this study, a modification was introduced to Lindquist’s procedure by incorporating Leps’ (1970) non-linear shear strength envelope for rockfill (or rock accumulation) to model the strength of completely blocky accumulated rock materials (VBP goes to 100%). The modified Lindquist approach was tested by determination of the factors of safety of hypothetical models of bimslopes.

Nowadays bimrocks are widely used as a backfill material for artificial slopes and embankments, making the assessment of their shear strength properties a fundamental step for evaluating the stability of such structures. Improved 2-D and 3-D limit equilibrium methods, revised with respect to previous studies to account for the difference in the peak pushing horizontal forces during the two loading cycles of the test, were applied to revise the assessment of shear strength parameters of some bimrocks during bimtests carried out in 2011. The number of sections required in the 2-D method was determined on the basis of the relative errors of estimated strength parameters in comparison to those deriving from a 2-D analysis considering a very large amount of sections (i.e. 80 sections). The results show that neglecting the difference between the pushing horizontal forces recorded during the two loading cycles, as done in the previous researches, can produce relatively large errors in the back-calculated strength properties, especially for the cohesion term.

Anchored wire meshes are commonly adopted to stabilise potentially unstable slopes in granular soils. In most of the cases, this reinforcement technique is employed either as an active or a passive anchoring system. In both cases, the definition of a characteristic curve putting in relation the stabilizing force with the displacement of the soil in the “far field” is crucial. To optimize the employment of these reinforcement techniques, the authors performed a series of 3D FEM numerical analyses aimed at highlighting the interaction mechanisms developing between soil and stabilizing system. To correctly reproduce the mechanical response of the wire mesh, this latter is modelled as a membrane and the numerical analyses are performed by employing a large displacement approach. The soil mechanical behaviour is modelled by means of an elastic perfectly plastic constitutive relationship: the failure condition is described by means of the Mohr Coulomb criterion and the flow rule is assumed to be non-associated.

The present study focused on measuring free-field vibration induced by ground improvement work. Ground improvement work at the Indian Institute of Technology Patna campus was performed using the vibroflotation technique. Two different types of sensors were used to measure this ground accelerations and peak particle velocity (PPV). The minimum source to site distance of the recorded free-field peak ground acceleration (PGA) and PPV was 20 m and 10 m respectively. However, the data were recorded up to a maximum distance of 94 m for PPV and 70 m for PGA. The measured peak acceleration has been varied between 12 mm/s2 to 4010 mm/s2, and peak particle velocity varies between 0.08 to 5.94 mm/sec. The results indicate that the peak particle velocity reduces rapidly with the distance and about 93% reduction occurs in PPV at 56 m distance. However, the peak acceleration reduces by 80% approximately at about 58 m distance from the source. It has been concluded from the results that with the increase in the distance from the source, the reduction in PPV is more significant as compared to PGA.

This paper provides an analytical solution to predict the free strain consolidation of a stone column supported soft soil under plane strain configuration. The external load on the ground surface was assumed to be applied instantly, which results in time-independent but space-dependent total stresses in the composite ground. A rigorous analytical solution to evaluate the changes of excess pore water pressure with time at any point in the model was derived as a double series, using the method of separation of variables. The obtained solution can capture any distribution patterns of total stresses caused by the external load, where the total stresses are described as separable functions against spatial coordinates. The validation of the proposed solution was exhibited through an example evaluating the effect of change patterns of the total stresses with depth on consolidation of the composite ground. The calculation results were presented graphically in terms of average degree of consolidation for column and for soft soil, and average differential settlement between the column and soil regions. The more diminution of the total stresses with depth led to accelerated consolidation of the composite ground and more significant reduction in the average differential settlement between the column and the soil.

The construction of geosynthetic-reinforced soil bridge abutments have been receiving increased attention and interest, mainly because these structures can be put into service quickly and are an economic alternative to conventional bridge abutments. This article reports the results of a full-scale instrumented geosynthetic-reinforced soil bridge abutment in Slovenia. A 16-m-long concrete bridge was constructed in 2018 in the town of Sodna Vas, Slovenia. The geosynthetic reinforced soil bridge abutment was seated on a saturated soft foundation layer. The lower part of the abutment was embedded in the ground, while the upper part was constructed with rock facing. The design computation procedure was conducted by using the optimization method. The performance of the geosynthetic-reinforced soil bridge abutment was monitored during construction and loading. The predicted reinforcement loads, according to the guidelines, were compared to the measured reinforcement loads. The field-measured loads were smaller than those predicted by the design method.

In the design of earth embankments on soft soil strata, piles are often employed as settlements reducers. Despite of their well-documented effectiveness, the complex interaction processes transferring loads to piles within both the embankment and the soft foundation soil, are not yet totally understood. As it is well known, the effectiveness of this intervention is strictly related to the construction rate. In fact, the consolidation process taking place in the foundation soil induces the accumulation of settlements with time. The settlements increment at the embankment base, induces stresses migration towards the pile.In this paper, the results of an extensive numerical campaign performed by using a 3D finite difference code are presented. The numerical model allows to calculate the differential settlements at the top of the embankment and to appreciate the effects of both the consolidation and the construction processes.

Rigid piles are used to alleviate the detrimental characteristics of soft soil. Recently, the use of piled embankments has increased by many folds, as it facilitates rapid construction without compromising on serviceability. In the piled embankment, soil arching mechanism between adjacent piles improves the load-transfer to the piles and reduces the stress applied to the soft soil. In this study, a two-dimensional plane strain finite element model is adopted to investigate the mechanism of soil arching in a piled embankment. An idealized unit cell model is used to simulate the pile-supported embankment. The effect of different characteristics of piles and embankment soil are assessed. The outcome shows that friction angle, and embankment modulus significantly affects soil arching. Inconsistency among existing design approaches in the literature is highlighted.

A series of numerical analysis was performed to investigate the vertical stress distribution on stiffened deep cement mixing (SDCM) column under embankment load. The transfer of vertical load on SDCM column was estimated based on stress reduction ratio (SRR). The parameters related to behavior of SDCM column: height and modulus of embankment fill, stiffness of core pile and DCM layer, area of core pile, were focused on the investigation. The results showed that SRR decreased with increasing elastic modulus of embankment fill and core pile, in which SRR in SDCM column was lower than that in DCM column at a given elastic modulus of fill and core pile. The analysis results presented that SRR decreased nonlinearly with increasing the cross section area of core pile. The numerical results indicated that the utilization of SDCM column to support embankment over soft clay resulted in a more efficient transfer in an arching mechanism.

Vertical drains are often used to accelerate the pre-consolidation settlements in soft clay soils. The coefficient of radial consolidation (Cr) is one of the important parameters that governs the rate of settlement. Several researchers have proposed different methods to estimate the coefficient of radial consolidation. This paper attempts to compare the Cr value and ultimate settlement (Sf) by two empirical methods using data from an instrumented field test. The field data was obtained from the marine reclamation project for the extension of existing port at Mumbai, India. Prefabricated Vertical Drains (PVDs) along with preloading was successfully applied at the site to consolidate the soil. Cr values were calculated from the deformation data measured beneath an embankment through field instrumentations such as settlement plates. Many studies reveal that the laboratory test value deviates from the actual field value due to size effect and other factors hence, it is of utmost importance to determine more representative value of Cr from back analysis of field measurements. The degree of matching and the discrepancies in the values of Cr and Sf obtained from various available methods is described in the current paper.

The high-speed rail (HSR) is one of the most significant technological advancements in the field of transportation, which is continuously gaining popularity worldwide. A major challenge to the development of HSR in any country is the selection of an appropriate railway track. Although ballastless/slab tracks are especially dedicated for the HSR operations, they have a few shortcomings such as, high initial construction costs, inability to align itself according to the ground movement, generation of higher levels of noise and vibration than the ballasted tracks. An alternative strategy is to strengthen the existing tracks to accommodate high-speed traffic. The present article investigates the adequacy of using geosynthetics and recycled concrete aggregates to improve the performance of the ballasted rail tracks for HSR operations. Two-dimensional finite element analysis is employed to examine the effectiveness of using geogrids, geocells, and recycled concrete aggregates in the ballasted railway tracks. The efficacy is evaluated in terms of the track settlement. The results indicate that the use of recycled aggregates and geosynthetics significantly reduce the track settlement and may permit a higher train speed for same allowable settlement. The maximum reduction in track settlement is observed with geocell reinforced capping followed by the capping layer composed of recycled aggregates and the geogrid reinforced capping. Thus, the present study shows that the geosynthetics and recycled concrete aggregates may offer cost-effective alternatives to improve the performance of ballasted railway tracks for high-speed rail operations.

The granular substructure layers in a ballasted railway track often undergo a large amount of lateral deformation due to insufficient confinement. This deformation results in a loss of track geometry and demands expensive maintenance work to ensure passenger safety and comfort. The cellular inclusions such as scrap tires and geocells can provide confinement to the granular substructure layers and increase their strength and stiffness. It is inevitable to evaluate the magnitude of improvement in strength and stiffness provided by these inclusions before their in-situ application. This article presents a mathematical model to determine the magnitude of extra confining pressure offered by the inclusions under the three-dimensional stress state. The model is validated by comparison with the results of experimental investigations on the cellular inclusion reinforced soils. The parametric study of the variables affecting the performance of cellular inclusions reveals that the magnitude of additional confinement significantly depends on the stress state, inclusion and infill soil properties. The present model can be employed for the selection of optimum material parameters for achieving the desired magnitude of confinement from the cellular inclusions.

The paper shows a global method that allows to take into account the stabilizing effect of the retaining structure, independently of its location. This method of analysis, which can be generalized to any type of retaining structure, allows to obtain the variation of force developed at each structural element as a function of the variation of the safety of the slope and of the movement associated to the structure.

Rock bolting is a ground reinforcement technique broadly used not only in mining but also in civil engineering applications. A rock bolt consists of a bar inserted in a borehole that is drilled into the surrounding soil or rock mass and secured to it generally with a binder, which can be cementitious or resin based. Cementitious grouts require several hours to harden and resin cartridges might lead to shortcoming such as poor mixing, collapsed boreholes prior to insertion, and insufficient resin volume for full encapsulation due to enlarged boreholes. A novel pumpable thixotropic resin based on polyurea silicate has been developed in order to overcome the issues of conventional resin cartridges, to ensure a quick curing time within seconds and to be able to install bolts on the roof. Several mechanical pull-out tests on hollow and solid rock bolts according to DIN 21521 have been performed in order to assess the ultimate failure for the novel pumpable thixotropic resin. Results are very useful to contractors and designers to understand the mechanical response of a novel thixotropic resin.

The application of geogrids and steel wire meshes is widespread in the civil and environmental sectors. Their use ranges from reinforced soil embankments to rockfall protection and even more. The use of geogrids and double twist steel wire meshes can be combined with concrete panels, anchors and piles for several applications. Some important examples in which infrastructure projects were designed with the use of numerical modelling are the Tana Toraja Airport Embankment in Indonesia and the Railway Embankment in Soekarno-Hatta Airport Project. It is in the interest of the manufacturer that the designer has the knowledge for a proper selection and use of the materials. The design tensile strength TD and the axial stiffness EA are the main parameters for the numerical modelling of geotechnical applications with geogrids and double twist steel wire meshes. The design tensile strength TD and the axial stiffness EA can be calculated starting from the ultimate tensile strength TULT and the corresponding ultimate strain εULT provided by the manufacturer. An advanced numerical modelling can be performed by implementing the stress-strain curves of the products at different stages (such as 24 h, 1000 h and 120 years) in the non-linear static analysis to model the creep deformations of geogrids.

This paper deals with the one-dimensional primary consolidation of saturated fine-grained soils, described as a discontinuum process. The theory is based on two foundations: the ideal discrete space-time structure of matter, and the principle of the mean value. Discontinuous matter is described by the influence domain of a point or node. Since this domain is a statistical sample of the whole discontinuous body, any associated quantity may be described properly as a point estimator, which is determined by averaging the neighboring values within the influence domain. As a consequence, a parabolic differential equation is attained. When this estimator is linear and logarithmically related to the excess porewater pressure, the settlement, or the vertical strain of a fine-grained soil subjected to the consolidometer test, the theories proposed by Terzaghi, Davis and Raymond, and Mikasa can be weighed, and the abundant reported experimental data may be used to develop deductive relationships between the consolidation parameters.

The response of shallow geotechnical structures is affected by the interaction with the atmosphere. Since the ground surface is very often vegetated, plant transpiration plays a major role in the removal of soil water by the atmosphere. The soil, plant, and atmosphere form a continuum and modelling the hydraulic boundary conditions associated with vegetation requires an understanding of the water flow processes taking place from the soil through the plant xylem up to the leaves. The measurement of the water content and the (negative) water pressure in the soil-plant continuum system therefore becomes a critical aspect in assessing soil-atmosphere interaction. This paper presents a pilot study of a novel integrated portable system for simultaneous monitoring of i) water content in the ground, using TDR probes and ERT surveys; ii) xylem water pressure (in the plant) using High-Capacity Tensiometers and Thermocouple Psychrometer, and; iii) leaf water pressure using the Pressure Chamber.

Osmosis is known to play a key role in reducing the transport rate of contaminants through the natural and engineered clay barriers that are used for a number of geoenvironmental applications, such as the lining of landfills and the deep geological disposal of radioactive wastes. Although a significant body of experimental research has focused on the quantification of osmotic phenomena in smectite clays permeated with single-electrolyte solutions, no evidence has been provided about the membrane behaviour of clays in solute mixtures and, specifically, about the so-called osmotic anomalies (i.e. membrane efficiency coefficient outside the 0 to 1 range) that have been documented in the biological and chemical literature for fine-porous charged diaphragms in the presence of two or more electrolytes. In view of the similarities between such fine-porous media and smectite clays, the aim of the paper is to discuss the conditions under which bentonite-based barriers are expected to exhibit the aforementioned osmotic anomalies, which are shown to be caused by the different diffusivities and electrochemical valences of the migrating cations.

The know-how about the influence of ice-content on thermo-hydro-mechanical characteristics of soils in their frozen state is discerned to be essential for various situations in the realm of geomechanics (viz., slope instability, foundations in the permafrost regions and ground modification by freezing, etc.). Hence, to capture the influence of ice-content on shear strength characteristics of soils, the conventional direct-shear box setup has been suitably modified. Though this setup, designated as DSBTemp, is an inexpensive setup, it has been found to be a very handy and promising tool for investigating the effect of volumetric ice content, θI on the shear-strength characteristics (viz., peak shear strength, τp, dilation angle, ψ) of soils in their frozen state. Details of fabrication of the DSBTemp along with some preliminary results on fine-sands are presented in this paper.

In mountain areas, rock glaciers are markers of climate change. Besides temperature effect, their surface flow velocity can be influenced by ice proportion and other mechanical and physical properties. To improve the understanding of the processes influencing thermal control and the seasonal and inter-annual variations, this study on the Laurichard rock glacier in France proposes the analysis of correlations between surface velocity variations and air temperature anomalies based on Staub et al. (2015), and evaluates the viscosity using surface velocities with steady shear flow hypothesis (Monnier et al. 2016) over 30 years of measurements.

Because of ignoring the vapor migration in freezing soils, coarse-grained soils have long been deemed not susceptible to frost heave. However, recent studies reveal that vapor migration can increase the total water content and lead to remarkable frost heave hazards in coarse-grained soils. In this paper, a new numerical model is developed based on the coupled thermal and hydrological processes. The soil water characteristic curve and the soil freezing characteristic curve are taken into account in this model. The model is established by using COMSOL Multiphysics which contains 5 equations and 5 variables. In order to validate the numerical model, laboratory experiments were performed in coarse-grained soils. The result shows that there are sharp increases in water content at the top of samples and the freezing front. A good match between measured and computed results indicates that the new model can make a good explanation for the coupled movement of heat and moisture in coarse-grained soils.

Molecular diffusion can transport ions from the leachate through a compacted soil barrier in landfills since it depends only on the concentration gradient. This mechanism is described by equations that depend on the effective diffusion coefficient in soils for each chemical element. Laboratory tests are necessary to estimate this coefficient, by testing a compacted soil layer subject to a contaminating solute, which results in curves of the variation of the concentration over time and along the soil thickness. The purpose of the paper is to apply the semi-analytical method called Equivalent Contaminated Layer Solution (ECL) for determining the diffusion and sorption coefficients for specific contaminants. It was adjusted a computational model that allows the calibration and visualization of diffusive tests in time and space, with a three-dimensional surface. The methodology was carried out using the software Wolfram Mathematica. The experimental data used were taken from previous studies. It was modelled the diffusion of chloride, chrome, cadmium, nickel and copper. The results of the models were validated for a hypothetical compacted clayey liner. The method applied allowed us to analyse the ion migration in compacted clayey liners from solid waste landfills.

The research we present in this paper is part of a wider project about the modelling of climate change effects on the degradation of permafrost, with particular attention for the stability of rock masses. The presence of ice and/or mixtures of ice and granular materials in rock joints has a big impact on the shear resistance of joints and on the evolution of joint persistence. In previous research we modelled the mechanical behavior of ice and frozen soils with a Distinct Element model and compared the evolution of the resistance with ice content with experimental data available in the literature. In this paper, we are focusing on rock joints and we are modelling both fill material (ice and frozen soil mixtures) and rock as collections of Distinct Elements, taking advantage of the previous experience in terms of calibration of the parameters. In particular, in this preliminary study, we will focus on the shear resistance of joints as a function of the composition of the fill material. The purpose of this research is to study the mechanical behavior of joints and derive the corresponding force-displacement relationship to be assigned to the interfaces between blocks in a full scale model of rock masses.

Shallow foundations are one of the most common methods for transmitting loads of structures to the underlying ground. Design standards are often based on the bearing capacity of shallow foundations in saturated soils or dry soils. However, many shallow foundations are located within unsaturated soil above the groundwater table. Although experimental studies show that the bearing capacity is significantly increased by the presence of suction in unsaturated soils, the foundation settlement caused by infiltration, e.g., due to rainfall and pipe leaking, may develop further problems for structures, such as wall cracks, sticking windows and doors and the presence of water in basements. This kind of damage is happening more often now, with more extreme weather conditions as a result of climate change. A finite element model has been developed in this paper to analyse shallow foundation behaviour under infiltration conditions. An advanced unsaturated soil model has been implemented in the finite element code that considers the soil-water retention with hysteresis and deformation dependency. Numerical analysis results indicate that the foundation settlement is significantly influenced by the hydraulic history (seasonal changes with drying-wetting cycles), and hydraulic hysteresis should be included in the numerical analysis of the mechanical response of shallow foundations in unsaturated soils.

Oil shales are sedimentary rocks containing kerogen, a precursor to crude oil trapped in the inorganic mineral matrix. Green River formation in Utah, Wyoming, and Colorado is the largest deposit of oil shale in the world. The current extraction of shale oil involves the pyrolytic extraction of kerogen from the mineral matrix, which is expensive and detrimental to the environment. A better understanding of kerogen-mineral interactions could lead to more efficient extraction techniques. Our experiments indicate that the size of kerogen “pockets” is of the order of 10s of nanometers in the mineral matrix and also, the in situ kerogen is strongly influenced by molecular interactions with the surrounding minerals. A three-dimensional molecular kerogen model of Type I has been developed to determine the molecular interactions with predominant minerals (Na-montmorillonite clay, quartz, and calcite) of Green River oil shale. These molecular interactions are analyzed based on the seven fragments and associated independent ammonium ions that constitute kerogen. The results indicate that the interactions of kerogen molecules vary with the mineral in proximity, and also the underlying mechanisms are different. Techniques for the efficient extraction of kerogen can be developed by understanding the binding interactions between the kerogen and minerals.

This paper presents the effect of burial depth on the response of conventional buried pipelines under strike-slip fault rupture and also proposes a mitigation method using geofoam blocks to safeguard buried pipelines. The performance of the buried pipelines is assessed using three-dimensional numerical simulation using ABAQUS. The configuration of geofoam blocks for protection consists of two blocks at each side of the pipeline and one block on the top of pipeline. The results shows that although the conventional buried pipeline failed due to fault rupture as a result of excessive compressive strain as well as local buckling within the pipe wall, geofoam blocks could successfully reduce the compressive and tensile strains along the pipeline satisfying the design requirements.

Advanced simulation of geotechnical problems involving clay may require sophisticated constitutive models in order to accurately capture the mechanical response of soil under various loading conditions, initial states and strain levels. This is of particular importance when numerical analyses involve an interaction of soil and structure possibly including large deformations and dynamic (cyclic) and impact loadings prevalent in most offshore geotechnical applications. Accordingly, some advanced soil models have been implemented into a bespoke finite element code and then applied to several dynamic coupled problems of geomechanics. This has provided more realistic numerical analyses for which different features of soil behavior have been taken into account. This paper presents some of these numerical simulations highlighting the importance of advanced soil constitutive models in geomechanics.

In closed-loop Ground Source Heat Pump system, the thermal exchange between the building and the subsoil is provided by ground heat exchangers inserted into the ground with a circulating heat-carrier fluid. A heat pump manages the system by regulating the fluid working temperature. When a greater heat extraction rate from the subsoil is needed, the fluid working temperature can be lowered down to −5 °C by adding anti-freezing additives. This way, the thermal alteration induced in the subsoil is more intense and can lead to freezing processes in the surrounding ground. The geotechnical properties of sediments with significant clay fraction are irreversibly affected by the occurring alterations in the internal structure and porosity distribution that are caused by the freeze-thaw cycles. A series of experimental tests have been conducted to study vertical deformations and permeability variations induced by freeze-thaw cycles in Over-Consolidated silty clays at different Over-Consolidation Ratios (OCR). Whilst in Normal-Consolidated silty clays an irreversible settlement up to 16% is gathered cycle after cycle depending on sediment plasticity, pore fluid salinity and applied load, the OC silty-clays show an opposite behavior. Experimental results point out that, in case of OC deposits, higher the OCR lower the freeze-thaw induced settlement. In case of OCR > 15, the settlement turns to a slight expansion. Conversely, the observed augment in vertical permeability increases with the OCR degree.

As open space in urban areas is very rare and mobility requirements are constantly increasing, new infrastructures are being planned and constructed in the subsurface. These underground infrastructures may additionally be used as Shallow Geothermal Energy systems (SGE) to exchange and store heat. For real-world tunnel set-ups in the urban agglomeration of Basel (Switzerland), optimal closed and open SGE systems were evaluated depending on the type of tunnel infrastructure (motorway or railway) as well as geological and hydrogeological settings. This contribution illustrates strategies for seasonal Thermal Energy Storage (TES) in solid rock layers at depth of approx. 25 and 35 m by combination of Tunnel Absorber Segments (TAS), and very shallow Borehole Heat Exchangers (BHE). Investigations focus on the efficiency of the TES systems where the BHE extracts heat injected by TAS. First results suggest that thermal energy of up to 290 W could be recovered by the simulated double-U-loop BHE. Furthermore, TES system efficiency can reach values of up to 10.2%. The here presented performance analysis provides preliminary evaluation elements of SGE combined use as a further step for spatiotemporal thermal management in realistic urban settings.

Effective thermal conductivity (ETC) is affected by interparticle connectivity in granular geomaterials, which can be characterised by coordination number. Complex network theory can be used to identify “features” that are also able to quantify the particle connectivity. However, this new class of variables have not been used to study the effective thermal conductivity in real sands. An advantage of some network features is that they can simultaneously consider both the particle connectivity and contact quality by adding a contact area or thermal conductance as a weight to connectivity variables. In this paper, weighted closeness centrality extracted from the computed tomography images of five natural sands is shown to be a good predictor of ETC of the sands.

Numerical investigation of crack damage development and micro-fracturing in brittle rocks is a widely studied topic, given the number of applications involved. In the framework of the Discrete Element Method (DEM) formulation, the grain-based distinct element model with random polygonal blocks can represent an alternative to the Bonded-Particle Model (BPM) based on particles. Recently, a new engine called Neper has been made available for generating 3D Voronoi grains. The aim of this study is to investigate the applicability of a Neper-based 3D Voronoi tessellation technique for the simulation of the mechanical macro response of rocks. Simulation of unconfined compression tests on synthetic specimens is conducted and a calibration procedure tested. The issue related to scale effects is also addressed, with an application to the case study of a deep geothermal reservoir.

A hydraulic fracturing site in Morgantown, West Virginia, USA was selected to be a research site for the Marcellus Shale Energy and Environment Laboratory (MSEEL) project which was funded by the U.S. Department of Energy (DOE). The field site has two previously drilled horizontal wells and two newly drilled horizontal wells for extracting natural gas. A separate exploratory vertical “science well” was also drilled and an array of geophones was used to extract important seismic/microseismic event information during hydraulic fracture propagation. Microseismic data collected from the geophones was then used to approximate the extent of hydraulic fractures. Numerical modeling was performed to determine the extent of all hydraulic fractures at the site. The 58 stages encompassing two wells were individually numerically modeled. Available geologic, geomechanical, and treatment data was utilized in the numerical modeling of all stages at both horizontal wells. Comparisons were then made with available microseismic data collected at the field site during hydraulic fracturing operations. Model calibration was based on a statistical methodology and available microseismic data. Results show a good match between estimates/measurements and model calculations of fracture/microseismic cloud height.

Geomechanical evaluation of CO2 underground disposal is complex and can be even more challenging in coal reservoirs due to natural fractures and combined effects of multi-component transport. The objective of the research work presented in this paper is to investigate the geomechanical response of the geologic system due to large-scale CO2 injection in a targeted coal reservoir. Field-scale geomechanical models were constructed to capture overall geologic response at an active site due to injection, and the results were compared with long-term field monitoring work. Coupled multiphase fluid flow and geomechanical models developed for the project site are capable to understand the CO2 transport behavior within the targeted reservoir and geologic layers above the targeted reservoir. Additionally, modeling efforts were carried out to investigate CO2 transport behavior and geomechanical response, if CO2 were to break through the seal layer into overburden formations. The combined results of geomechanical modeling and tiltmeter monitoring provide useful information on the migration of CO2. Modeling results show that a secondary coal seam above the targeted coal reservoir could potentially acts as a barrier in the presence of a CO2 leakage.

Compressed air energy storage (CAES) is considered as a promising energy storage solution to balance the energy load leveling. The previous engineering practice usually locates the air storage caverns at deep locations from the surface of the earth. This study conducts a numerical analysis to evaluate the possibility of building a rock cavern for compressed air energy storage at a shallow depth. The results show the sealing layer could stop the compressed air from leaking out and contain the heat energy in the storage cavern due to its excellent adiabatic performance. The heat transfer in the structures of the cavern had a hysteresis effect which should not be neglected in the further study. The stress and strain in the surrounding rock were both within the capabilities of the materials. The results confirmed the feasibility of CAES in the lined rock caverns at shallow depth from the aspect of the numerical simulation. It provides a theoretical basis for the following pilot cavern.

The service life of geothermal wells is affected by the reservoir permeability. Acid fracturing has been utilized to improve productivity in fractured carbonate geothermal reservoirs recently. A modeling method for the coupled thermal-hydro-mechanical-chemical (THMC) process during acid fracturing is developed. In a benchmark test, the effect of aperture heterogeneity on the efficiency of acid fracturing in geothermal reservoirs is examined. The results show that the acid flow and aperture increase exhibit significant anisotropy in the heterogeneous characteristics. Based on a field test of acid fracturing in a geothermal well, Tongzhou, Beijing, we use the built three-dimensional fractured porous reservoir model to simulate the process of acid fracturing. The agreement between the simulation and the field test data demonstrate that the proposed modeling method is capable of simulating acid fracturing in fractured carbonate geothermal reservoirs.

The need of renewable energy sources is increasingly pushing the design of new and renovated buildings as a result of compelling regulation in the construction sector. On the one hand shallow geothermal energy is suitable as a sustainable and distributed energy source. On the other hand, significant installation cost related to drilling of traditional installations represent a hampering factor. Energy geostructures as piles, diaphragm wall, tunnels and anchors include these costs in the construction of primary or secondary structural elements. Major part of building heritage in urban areas present underground levels that can be equipped with heat exchangers.This paper introduces the concept of a modular very shallow geothermal exchanger as part of a Heating, Ventilation and Air Conditioning (HVAC) system. The system is conceived to externally equip with heat exchangers the earth-contact area of underground walls that are generally widely available in residential and commercial buildings. An experimental site consisting of three modules of the above mentioned technology was designed by the authors and installed in an office building in Torino (Italy). Pipes were placed externally to the basement wall in two different arrangements. A large number of sensors were placed to monitor the additional stresses and strains on the wall and the thermal regime of the partly saturated ground volume involved in heat exchange. A comprehensive view of the main components of the prototype and the related monitoring system are given together with preliminary thermal performance results.

Roads and paved surfaces in cold climate are exposed to the formation of ice and snow deposition. These phenomena are related to high risks for vehicles and road users due to reduced friction. Deicing techniques are up to now mainly based on chemicals, especially salt. These substances induce chemical decay of concrete infrastructure elements and environmental harm. In order to overcome these drawbacks, the use of embedded hydraulic pipes with a hot carrier fluid below the paved surfaces has been proposed in last decades. This circuit can be part of a Ground Source Heat Pump (GSHP) system. Despite a number of examples of this technology have been proposed, very few of them included the application of energy tunnels. This paper focuses on the thermal activation of a tunnel lining in relation to an application for bridge deck deicing. A theoretical case study along an Alpine road has been considered as representative of a common situation of alternated bridges and tunnels. The numerical results show that the thermal activation of the tunnel lining can provide enough heat to keep the paved surface unfrozen even in protracted periods of low external temperatures.

The Turin metro Line 2 will extend for nearly 28 km and include 26 stations. It will connect the SW suburbs of the city to the NE ones. The excavation will be performed by means of TBM and Cut & Cover techniques and, once concluded, will host a fully automated driverless light metro. This paper will describe the feasibility study carried out to assess the energy potential of the thermal activation of the line by using an innovative tunnel lining segment (ENERTUN) recently patented and tested in real operating conditions. A novel methodology was adopted, involving thermo-hydraulic 3D FE numerical analyses to identify the geothermal potential for the different sections of the line. A study of the possible collectors for the thermal energy produced was also performed considering the planned stations, the existing buildings and the future urban developments.

Shallow geothermal energy systems are known to efficiently provide renewable energy for heating and cooling purposes. Energy geo-structures constitute a relatively recent application of these systems where the use of traditional purpose-made boreholes or trenches as ground heat exchangers (GHEs) is minimised or avoided by incorporating geothermal piping in underground structural elements such as piles, retaining walls and tunnels. This study explores the application of energy tunnels in the M4 – M5 Link project in New South Wales, Australia, which includes the construction of twin motorway tunnels of around 7.5 km in length for up to 4 lanes of traffic. The presented work examines this premise in detail by utilising advanced numerical modelling approaches and high-performance computing applications to investigate the long-term applicability of energy tunnels for this case study. The results indicate that thermally activating the entire tunnel could provide up to about 38.6 GWh per year for heating and cooling. A number of pipe configurations are also investigated, suggesting that placing the pipes only on either side of lining of the tunnel (as opposite to top or bottom) can result in a better thermal performance due to thermal interference and in this case provide up to about 17.5 GWh per year.

Energy geostructures are an innovative and sustainable renewable energy technology that has been demonstrated to be a successful solution for heating and cooling of buildings while contributing to CO2 emissions reductions. Therefore, the advantages of the technology together with the existing successful implementation examples has led to an increase trend of implementation of these structures. Different types of structures and foundations have started to be used for energy equipping. The paper presents the preliminary considerations of a real project implementation of energy geostructures at the New Unit of an Emergency Hospital in Romania. A specific type of energy foundation system was implemented for structural and economic reasons, represented by isolated foundations on energy piles. Compared to the classical pile foundation with general raft on top, this system presents several differences and challenges in term of both energy and mechanical aspects. The purpose of the paper is to highlight the particularities of such energy foundation, focusing especially on the thermo-mechanical behavior of the piles.

Over the past twenty years, a substantial amount of research has been performed to expand the understanding and modelling capabilities of energy geostructures: innovative earth-contact structures that provide combined structural support and renewable energy supply. The numerical modelling of energy geostructures has been progressively improved in capabilities and effectiveness, representing a critical solution for any comprehensive analysis and design of such geostructures. However, despite the observed rise in computational capabilities, the numerical modelling of energy geostructures remains daunting, especially for the engineering practice. In this context, analytical solutions based on sound theoretical principles and validated through experimental evidence represent paramount tools for the analysis and design of energy geostructures. This paper summarises the only analytical solutions currently available for the analytical modelling of a key problem in the analysis and design of all energy geostructures: the response of such geostructures to the thermal and mechanical actions that are applied as a consequence of their structural support and energy supply. Cylindrical and plane energy geostructures, such as energy piles and walls (or slabs) are considered, respectively.

Energy piles (EPs), consisting in piled foundations equipped with heat exchangers, have been extensively studied in recent years, both from the thermo-mechanical response and energy performance points of view. However, most research refers to typical rotary bored, CFA or precast driven, medium diameter piles. Not much attention has been devoted to so-called energy micropiles (EMPs), representing an opportunity to provide at the same time energy and structural retrofitting to existing buildings. Existing studies show that EMPs overall may thermally perform differently to EPs, but they are comparable in terms of specific heat flux. In this work, a 3D FE numerical model is employed to perform a comprehensive parametric study considering design factors that are peculiar to EMPs, to assess the most important parameters to maximize their energy performance. The parameter space is efficiently explored resorting to a statistically-based Taguchi approach. Results show that thermal design of EMPs should not be based on the same criteria as those used for medium-large diameter EPs, since different parameters are dominant in enhancing their energy performance. In particular, the pipes diameter should be maximized in EMPs for its strong influence in results, while being very easy to engineer.

The application of thermally-activated pile foundations has received significant attention in the last decade with a number of large- and small-scale tests having been undertaken. Alongside these physical studies, a number of investigations utilising numerical analysis have been undertaken to examine the behaviour of single piles and pile groups. Focussing on studies examining single piles, it is apparent that a variety of differing domain dimensions have been used. The work presented in this paper had the objective of systematically examining the influence of the domain size and how it affects the predicted thermo-mechanical response of the pile. It shows that the domain size has an important impact on the initial distribution of mobilised shaft friction due to applied mechanical load which then impacts on the subsequent thermo-mechanical response.