Proceedings of GeoShanghai 2018 International Conference: Fundamentals of Soil Behaviours

The breakage matrix model has great potential in describing particle size degradation of granular materials. A series of one-dimensional compression tests were performed on uniformly graded calcareous sand to obtain the breakage matrix. This straightforward method has successfully predicted the particle size evolution of non-uniformly graded samples with different initial particle size distribution.

The strain localization phenomena in geotechnical engineering are always accompanied with strength softening behavior. When the strain localizations are simulated by finite element method within the framework of classical continuum theory, the numerical solutions suffer from poor convergence and serious mesh dependency problems. Whereas, as a regularization approach, the micropolar theory is used herein to improve the convergence property and the mesh dependency problems. In this paper, a critical-state based sand model is enhanced by the micropolar technique. Using this polarized model, strain localizations in biaxial tests are numerically conducted and compared with those from the classical continuum theory based model. Besides the regularization ability in dealing with mesh dependency problems, it has been also found that the strength of the micropolar continuum is stiffer than that of the classical continuum, especially in softening regime.

The shear resistance of fragmented gravels at the base of landslides plays an important role in landslide dynamics, especially in increasing granular propagation speeds and final runout distances. While many site investigations and theoretical analyses have attempted to explain the intrinsic mechanism of these phenomena, the current paper presents numerical simulations of the mechanical response of fragmented gravels via the Discrete Element Method (DEM) under the drained triaxial compression conditions. It is evident that the non-fragmented gravel mass has relatively large initial void ratio, high peak and residual shear strengths, and large shear contraction and dilation volumetric strains. However, for the fragmented gravels, they behave oppositely. In the analyses, it is clear to see that the peak and residual shear strength, the maximum shear contraction volumetric strains correlate with the fraction of fragmented gravels perfectly by parabolic curves. The current numerical results can qualitatively explain the shear resistance reduction of fragmented gravels during landslides.

An extended constitutive model is proposed to describe the four different behaviours of rock and soil. Four parameters of the extended constitutive model are calibrated according to the correlation coefficient between the behaviours described by the model and experimental data. Based on an analysis, a ‘quasi-stress and quasi-strain’ relation is proposed to describe the post-failure behaviour of rock and soil. Test results showed that the model is suitable for representing the behaviour of rock and soil and can be used as a reference for the virtual internal bond model, spring model, damage model, discrete element method, etc.

In this study, a series of laboratory tests is conducted to examine the characteristics of mixtures composed of glass beads (GB) and polyurethane beads (PB) in different size ratios (sr = D50-GB/D50-PB). Specimens are prepared in the same relative density but in various weight ratios between GB and PB called polyurethane content, PC (= WPB/WMixture = 0, 0.5, 1.0, 2.0, and 5.0%). Small-strain shear modulus Gmax is estimated by the shear wave velocity measured by bender elements installed in an oedometer cell with various confinements under K0-loading condition. The normalized shear modulus (G/Gmax) is also measured by a resonant column test. It is found that the behavior of mixtures could be divided into two regions as the contact control and the stress control by a value of “stress threshold” that decreases with an increase in PC due to the large deformation of polyurethane particles. Additionally, with the participation of PB, the mixtures experience a sudden rise in Λ factor incorporated with a small value of ζ exponent in the Gmax = Λ(σv/1 kPa)ζ at polyurethane content, PC ≈ 0.5–2%, indicating the optimum packing and minimum sensitivity to confining pressure of the mixture. Although PB works as a low stiffness material, they play an important role to enhance inter-particle contact behaviors, resulting in an increase of stiffness degradation at low stress range. However, the deformation of PB at high confinement causes a reduction in G/Gmax curves.

Granular materials exist extensively in nature and the particle shape has great influence on the mechanical property of granular materials. In order to study the influence of particle shape on the mechanical property of granular materials and establish the relationships between the micro-parameters of particle shape and macro-parameters of the mechanical property of granular materials, a 3D shape quantitative method based on two-dimensional analysis was proposed, by which the granular shape of same materials and three types of particles (sphere, elliptic cylinder and plate) was described. The direct shear tests were done under the same relative density and different normal loads, from which the rules of shear stress and dilatation with particle shape were found. The stress-dilatancy model was introduced and parameter $$ \upmu $$ representing friction angle of particles was revised to consider the influence of particle shape. The results show that the more irregular the particle shape, the higher the peak shear stress and peak vertical displacement. These macro-mechanical properties were resulted from the different particle boundaries and relative movements. At last, the relationship between the parameter $$ \upmu $$ of stress-dilatancy model and particle shape could be calculated. The parameter $$ \upmu $$ becomes larger as the particle shape becomes more irregular but its increasing rate becomes slower and slower.

In cement treated soil, bonding structures which consist of soil particles and cement hydrate affects the mechanical behaviors (peak strength, softening and dilatancy). Micro cracks of the bonding structure gradually appears with the development of deformation, which induces degradation of cementation strength. In this work, a coupled elastic-damage-plasticity effect is considered and evolution rules of cementation strength with plastic shear strain are proposed. In addition, within the framework of the Super-Subloading Yield Surfaces, an elasto-plastic constitutive model is proposed for cement treated soil to consider other mechanical behaviors such as the decay of soil structure and loss of consolidation. Triaxial compression drained tests for cement treated soils under different confining pressure have been used to investigate the validity of the proposed model. A good agreement between the experimental results and the model is obtained. It can be found that the degradation of cementation affects the tendency of dilation. Higher confining pressure inhibited the development of the micro crack of the bonding structure.

Inspiration from biological systems has recently fuelled research in the built environment to develop smart materials that comprise sustainable and resilient systems, which similarly can continually adapt and respond to their environment. Many of these activities have so far focused on concrete for structural applications. However, to date there has been little work on the development of effective smart systems for geotechnical applications. Those systems and relevant geotechnical applications pose very different and more difficult and challenging problems compared to concrete and require a complete rethink of how to design such smart systems. The focus of the work reported in this paper is on the development and performance of self-immune and self-healing soil-cement systems subject to freeze-thaw (f-t) cycles. This was addressed with two types of microcapsules: SikaAer ® Solid and Lambson microcapsules. Unconfined compressive strength (UCS), water content and volume stability were investigated after f-t cycles. By adding 1% (by soil mass) Lambson microcapsule, the UCS of 20% cement stabilised soil samples subjected 1–12 f-t cycles was improved by 21–40%. The f-t durability was also largely improved by adding 1% (by soil mass) SikaAer ® Solid, where no deterioration in UCS was observed; change in volume and moisture content was largely reduced; and no crack formation was observed by optical microscopy after 10 f-t cycles. This study presents evidence of the significant potential for soil-cement system to possess self-immune or self-healing capabilities through the implementation of appropriate microcapsules.

This paper describes recent advances in geotechnical stability analysis that combine limit equilibrium analysis with finite element stress analysis to provide a factor of safety and the failure load. This method, known as the finite element limit equilibrium method, is used to propose and prove the necessary and sufficient conditions required for determining the limit equilibrium state for a slip surface of soil. Based on the limit equilibrium conditions along a slip surface, the method could be used to perform a slope stability analysis and to evaluate failure loading in rigid footings and retaining walls. After a brief outline of the methods, several representative two-dimensional examples are analyzed.

Bamboo-steel composite rockbolt (BSCR) has been used in many earthen site protection projects, however, there is little study on anchorage behavior of BSCR in real stress field. Due to the large diameter of BSCR, it can bear the tensile-lateral shearing coupled effect in engineering practices of reinforcing earthen sites. The purpose of this paper is to study the anchorage mechanism, deformation characteristics and failure modes of BSCR by the means of centrifugal model tests. In this study, two kinds of rockbolts were employed to reinforce soil slopes, one is organic glass rockbolt, which is rigorously scaled from BSCR basing on Buckingham π-theorem, the other is steel wire rockbolt, which can only provide the axial reinforcing effect, they have the same axial stiffness but different bending stiffness. On that basis, the distribution and evolution laws of axial stress/strain, bending moment etc. with the change of load were compared and analyzed. The influence of anchorage layers and stiffness on the anchorage performance was also discussed. The results show that the axial stess and the bending moment increase with the increase of the load. Besides, the rockbolts with a certain bending stiffness can improve the slope stability, so the anti-bending capacity of rockbolts should be considered. Furthermore, 2 layers of organic glass rockbolts can bear bigger load, and the failure mode is progressive failure of top-down. The output from this research will provide theoretical basis for the effective and optimal use of BSCR for the conservation of earthen sites.

A series of undrained multi-directional direct simple shear tests with circular paths were conducted to investigate the excess pore pressure generation and shear strain development in clean Hostun sands under multi-directional loading condition. The results of an example test are shown. The excess pore pressure accumulation and shear strain development under multi-directional loading condition exhibits evidently different characteristics compared with that under uni-directional loading condition. Excess pore pressure accumulates generally with the circular stress path but can have increase and decrease within a single cycle as well.

The increased reclamation in worldwide range induces significant consolidation and subsequent brings about serious settlement in the long term. In order to capture the consolidation characteristics by the surcharge method, a modified oedometer apparatus, which is allowed to measure the K 0 , elastic wave velocity, is employed to clarify the relationship among settlement elastic stiffness and K 0 . The variation of elastic wave velocity including shear wave and compression wave velocity are recorded by bender-extender element. The signal is optimized and the crosstalk is eliminated in the tests. Due to the sensitivity in shear and compression wave velocity (V s and V p ) of the solid and fluid, the ratio of soil particle to water is indicated by variation of V p and V s during the loading. Overall, the preliminary results show that the bender extend element is a sound tool to record the elastic wave velocity and derived elastic stiffness. The mutative K 0 can be monitored obviously.

Caisson foundation is a cost-effective alternative to conventional foundation for offshore structures. The bearing behavior of caisson foundation under combined loading is important for design. This paper aims at predicting the mechanical characteristics of caisson foundation by using discrete element method and analyzing the micro particle behaviors to understand the failure mechanism of the foundation in soil. Since the foundation soil is sand, discrete element method is adopted to model the loading tests with combined vertical loading, horizontal loading and moment. The numerical simulations are compared with experiments in terms of the trend of load-displacement curves and volume deformation curves. Then a series of micro analysis (including particle rotation field, particle displacement field, average particle rotation field, stress field and force chain distribution) are performed to investigate the failure mechanism of foundation with the insight of microstructure. Meanwhile, the influence of loading combination on failure is studied.

In this study, discrete element method is used to investigate the behavior of one-dimensional compression at high pressure. The breakage of a particle due to the multiple contacts is decided by the octahedral shear stress within the particle and a Weibull distribution of strengths. A multigenerational approach without using agglomerates is employed to model particle crushing, and a spawning procedure with volume compensation is applied. Effects of different initial void ratio, and the influence of particle crushing on the slope of the normal compression line were investigated. Evolution of distribution of normalized octahedral shear stress $$ (q^{{\prime }} ) $$ and its influence on particle crushing were used to analyze macroscopic behavior of samples. At the initial state of loading, $$ q^{{\prime }} $$ induced within each particle in the looser sample spreads out across a larger scope at the same vertical stress compared with denser samples. As particles inside samples begin to crush massively, statistical dispersion of $$ q^{{\prime }} $$ inside samples begins to increase for denser samples and achieve maximum at the failure stress and then statistical dispersion of $$ q^{{\prime }} $$ declines sharply when the vertical stress surpass the failure point for all samples.

Vehicle tires are one of the most bulky solid wastes which are increasingly produced along with car production. In order to reuse these materials, rubber shreds in mixture with sandy soils are widely used in geotechnical purposes due to their specific controlled compressibility characteristics and lightweight. Various laboratory studies have been carried out in order to obtain the optimized portion of sand or rubber content in mixtures. Restraining the compressibility of the mass in different structures such as backfills, road embankments, etc. is as crucial as the mass shear strength. Clearly different applied stress paths lead to changes in sand-rubber mixtures shear strength parameters. Considering the effective stress to be 100 kPa, the results of drained triaxial tests on sand alone and sand mixed with two different rubber wastes i.e. granulated rubber and rubber chips are presented in this study. Mixing ratio is chosen to be 30% of rubber in weight for both types of materials. The tests on sand alone samples yielded effective strength envelope which is approximately linear and can be defined by a friction angle of approximately 36.8°. Comparing two different applied stress paths, the resulted failure envelopes for mixed materials could be approximated by a bilinear envelope. Furthermore, the friction angle of chips rubber mixture samples is greater than sand alone, and for the granulated rubber it is less than that of sand and chips rubber mixtures for both applied stress paths.

The research conducted one-dimensional consolidation creep experiment for the marine soft soil in Tianjin to study the non-linear creep characteristics of soft clay there. The creep experiment was conducted in the mode of graded loading and adopted “Chen’s method” to process the measured data to get strain-time curve. The Merchant model was used to fit the strain-time curve to define model parameters and establish the relation between Merchant model parameters E0, E1, η1 and stress level. The non-linear creep model applicable to typical soft clay in coastal area in Tianjin was suggested to reveal the rule that the three parameters in the model approximately increase linearly with increase of stress level. Then based on this, the research established tridimensional non-linear viscoelasticity creep constitutive model reflecting time effect for marine soft soil in Tianjin and developed finite element subprogram, which produce result consistent with experimental data.

According to the Pasternak elastic foundation, a fractional derivative model for viscoelastic foundation is derived, and the equations of elastic and viscoelastic rectangular loaded plate on viscoelastic foundation with the fractional derivative Kelvin model are established. The dynamic equations of elastic and viscoelastic rectangular plate with four edges simply supported are solved by using the Galerkin method and the segmented numerical method. Then, the accuracy of the solution is verified by the case of free vibration. Besides, the influences of the fractional order, viscosity parameter, horizontal shear coefficient, and modulus parameter on the displacement of rectangular plate under dynamic load are analyzed. The results show that the fractional derivative model is able to describe the mechanical characteristics of viscoelastic material; the displacement of rectangular plate appears different attenuation before and after the fractional order is 0.5, and the attenuation speed of the displacement increases with the increasing of the viscosity parameter, horizontal shear parameter, and modulus parameter.

With a rapid development of economy in China in the past decades, some existing transportation system (e.g., highways, railways or airports) has been confronted with widening and rebuilding. In the process of roadway widening or rebuilding, subsoil would experience different stress paths due to excavation or backfilling. Thus the effect of stress path on mechanical properties of subsoil shall be considered in design. This paper presents a series of triaxial tests to investigate the influence of stress path on the mechanical properties of saturated silty clay. Soil samples were drilled from the area of the modern tram line in Suzhou high-tech district. The soil samples were prepared by remolding and consolidating under K0 condition. The soil behavior under four types of stress paths and the drainage conditions (i.e., drained and undrained conditions) were investigated. The results show that the saturated silty clay performed a strain hardening characteristic in an undrained condition irrespectively of the stress path. Under the drained condition, the Poisson ratio of soil varied in different stress paths. The development of pore pressure in soil had two patterns, i.e., the stable mode and the attenuation mode after reaching the peak value. The drainage conditions (i.e., drained and undrained conditions) had great influence on the initial tangent modulus of saturated silty clay under different stress paths.

Practice shows that the pore water pressure in soft clay is not often equal to the results given by the theoretical formula. The effects of buried depth on the pore water pressure in sand and remolded soft clay are analyzed through the centrifugal model tests. The results indicate that the pore water pressure in sand is equal to the hydrostatic pressure while the pore water pressure in soft clay is smaller than the theoretical value significantly. The pore water pressure in soft clay can be revised by the reduction coefficient that is related with the buried depth. The reduction coefficient of the pore water pressure in soft clay varies with depth until it is stable at 0.68 with depth of more than 10 m. Anti-floating design of underground should consider the reduction efficient of the pore water pressure in soft clay.

The soil-structure interface (SSI) is involved in many aspects of geotechnical engineering, with a range of efforts having been made to investigate the factors influencing its mechanical behavior. Its shear resistance and volumetric change are mainly governed by the soil properties. The particle shape emerges as an essential soil property affects various mechanical behaviors of the bulk soil, in terms of its compactness, the rotation of the particles, its shearing resistance, and so on. The particle shape effect must be properly considered as it pertains to the SSI issue. In this study, the interface shear tests are modeled using the three-dimensional (3D) discrete element method (DEM). Three types of clustered elements are used to represent the irregular particles, with the same relative density of the specimen being controlled before shearing. The effects of particle shape on the shear stress and volumetric deformation were analyzed, the specimen consisting of irregular elements showing a higher shearing resistance and larger dilation than the one consisting of spherical balls. The localization of shearing deformation was also investigated, with the finding that the thickness of the localized band is approximately four times that of the medium particle diameter.

The high-stress level caused by the pile penetration can result in grain breakage of sand around the pile, which is more serious for the very easily crushable sand. The grain breakage will lead to the reduction of pile bearing capacity, which can result in the instability of foundation structures even collapse. In this paper, a numerical analysis to investigate the problem of pile penetrating into the foundation of crushable sand is performed by adopting a newly developed sand breakage model combing with Coupled Eulerian-Lagrangian (CEL) method. Then the centrifuge pile penetration tests performed on Dog’bay carbonate sand was simulated by using CEL technique. The simulated results have a good agreement with the experimental measurements, which demonstrated that this numerical analysis for solving the pile penetrating is effective and feasible. All the simulated results show that the cone resistance is significantly decreased due to the grain breakage. Finally, it indicates that the numerical analysis is helpful for the design and construction of pile penetrating into crushable sand.

An experimental study was performed to determine the effect of adding nano SiO2 and cement to modify expansive soil. In order to get the basic properties of the soil, some soil tests were carried out to determine the basic physical properties. Also, SEM, XRD and Unconfined compression test were carried out to identify the underlying mechanisms. The test results of soil liquid limit and plastic limit1 classified soil as a medium expansive soil. The optimal water content and the maximum dry density is 24.6% and 1.47 g/cm3 respectively. The final average swelling ratio of two groups of expansive soil is 35%. Unconfined compression test is the ultimate strength of the soil sample under the condition of lateral restraint, experimental data showed that after adding 4% cement + 1% SiO2, and 3% cement + 2% nano SiO2, failure strength were 4326 kPa and 1400 kPa, respectively. XDR test data indicates that the major mineral in the soil is kaolinite, montmorrilonite, and dolomite. After modification, a new peak is incorporated which indicates the hydration products of cement-calcium-silica gel. While XRD patterns for the 4% cement + 1% nano silica and 3% cement + 2% nano silica modified soils are basically the same, but the intensity is not the same, which is consistent with the different amount of admixture. For the SEM image of soil samples with 4% cement and 1% nano silica soil, in comparison with the expansive soil and cement treatment soil, more dense soil surface structure was observed.

Bonding in structured soil limits the relative motion between soil particles as deformation develops with loading. This makes the structured soil behave differently from the reconstituted soil. Based on the unified hardening (UH) model for overconsolidated soils, a new model is proposed to describe the stress-strain relations of structured soil. The new model is developed from the following aspects: (a) a moving normal compression line (MNCL) paralleling to the traditional normal compression line (NCL) in e-lnp plane is proposed by introducing a structure potential parameter to describe soil structure collapse in isotropic compression; (b) a moving critical state line (MCSL) paralleling to the traditional critical state line (CSL) in p−q plane is proposed by introducing a bonding parameter to describe stress ratio evolution influenced by bonding in shear. This parameter is adopted in the dilatancy equation to consider the bonding-dependent dilatancy of structured soil. Both of the above 2 structure parameters have clear physical meanings and can be determined or estimated by conventional tests. It has been analyzed that the proposed model is able to smoothly and continuously reflect the positive/negative dilatancy and strain hardening/softening of structured soil influenced by bonding and its decay.

Step vacuum preloading (SVP) can effectively solve the problem of sludge plugging on prefabricated vertical drains in the process of the traditional vacuum preloading method for the consolidation of high-clay content dredger fill. The microstructure of dredger fill in the consolidation process of step vacuum preloading is constantly changing. To reveal the consolidation mechanism of SVP, the microstructural changes of dredger fill under the step vacuum pressure were studied at the microscopic level. However, most studies on the microstructure of soil concentrate on two-dimensional analysis which cannot accurately reflect the real situation of the microstructure. Three-dimensional studies do not only reflect the surface variations of the soil, but also greatly improve the utilization of other spatial information. SEM images of dredger fill at each vacuum preloading stage were obtained under a SVP indoor simulation test. The SEM images were modeled and displayed using ArcGis software. The 3D porosity of the dredger fill at each vacuum preloading stage was calculated using the area and volume method provided by geographic information system (GIS). The results show that 3D images of dredger fill based on GIS can significantly improve the fluctuations in microstructure than those achieved using 2D images. 3D porosity analysis is more realistic and reliable than the 2D method by which calculates porosity directly from the grayscale image of the dredger fill and avoids calculation error by threshold selection from inaccurate 2D analysis.

The strength properties of transversely isotropic soils are closely related to the loading direction. These direction-dependent properties have been testified by a series of laboratory tests. Two primary features for peak strength are obtained: the distortion of the strength curve on the deviatoric plane and the change of the internal friction angle associated with the direction angle between the major principal stress-acting plane and the depositional plane. How to describe these two features in a unified way is a difficult and hot research topic. This paper aims at solving this problem by proposing a strength parameter that was obtained by projecting the microstructure tensor on the direction of the spatial mobilized plane. It is an approach to extend an isotropic strength criterion into a transverse isotropy one. The combination of the proposed strength parameter with the isotropic non-linear unified strength criterion can well capture the distorted strength curve and its evolution with the increase of direction angle. The effects of the intermediated principle stress ratio b and the direction angle δ are also analysed. Material parameters in the proposed criterion can be conveniently obtained from the conventional laboratory tests. It is demonstrated that the new proposed criterion can be verified favorably by the test results.

Slope stability has gained more and more attention in geotechnical engineering, where the surcharge on the crest of slope may trigger slope failures. In this paper, the cemented-soil slope failure induced by footing surcharge was carefully studied using the two dimensional distinct element method (DEM). The main focus is on the effects of the footing position, footing roughness and slope angle on the slope failure mode and the bearing capacity. In addition, the micro-characteristics such as bond breakage were also examined to shed light on the underlying micro-mechanics. The simulation results show that the ultimate bearing capacity of the footing on the top of slope increases with the increase of the horizontal distance from the footing to the slope crest and the decrease of the slope angle. Once the surcharge is applied, the soils below the footing are compressed forming a triangular failure area. Simultaneously, cracks originate from the bottom of the footing and slope toe or slope surface, and then extend toward the middle part of the slope until a circular slip surface is formed eventually.

In order to clarify the failure mechanism of red clay slope under rainfall conditions, the stability of red clay slope under rainfall was studied by indoor model test and numerical simulation. To promote the situation, slope evolution, pore water pressure, shear stress and the research contents include the change of wetting front and the relationship between safety factor and rainfall duration. The results show that with the advance of rainfall duration, the advancing velocity of wetting front decreases gradually, which is inversely proportional to the rainfall duration. After the rain started, the slope of negative pore water pressure contour bending on the slope, and then gradually to the slope body forward, change curve of pore water pressure with depth is V, the pore water pressure of the slope is larger than the pore water pressure variation of the slope. The whole process of rainfall slope local damage, the foot to the plastic deformation, the slope in the upper part of the development, there is no obvious sliding surface and safety coefficient decreased with rainfall duration in advance, in the initial stage of the rainfall decreased rapidly, finally tends to be stable. The safety factor is greater than 1.25, and the whole slope is stable.

The reliability of geotechnical engineering may depend on the spatial variability of the soil properties. In this study, the effects of a site exploration program are assessed through how the spatial variability can be considered through numerical simulation. It is found that, the estimation accuracy of the mean and the standard deviation of a random field will increase as the sampling space increases. When the number of samples is the same, there is an optimal sampling spacing for estimation of the scale of the fluctuation. The effectiveness of a site exploration program also depends on the type of the geotechnical problem under consideration. If the characteristic length of the geotechnical problem is much smaller or larger than the scale of fluctuation, it is more effective to increase the sampling spacing. If the characteristic length is comparable to the scale of fluctuation, an optimal sampling spacing exists for a given number of samples.

This paper presents a novel constitutive model for modeling creep behaviour of granular materials. The model consists of a frictional part and a viscous part representing the frictional and the viscous stresses in granular media, respectively. The frictional part is a simple critical state hypoplastic constitutive model, while the viscous part is a rheological model. The proposed model is validated by simulating some element tests on granular soils. The new model can describe the three creep stages, namely primary, secondary, and tertiary creep, in a unified way.

This paper presents an exact analytical solution for the drained cylindrical cavity expansion problem using the well-known anisotropic modified Cam Clay model proposed by Dafalias (1987). The prominent feature of this elastoplastic model, i.e., its capability to describe both the initial anisotropy and stress-induced anisotropy of soils, makes the anisotropic elastoplastic solution derived herein for the cavity problem a more realistic one. Following the novel solution scheme developed by Chen and Abousleiman (2013) that links between the Eulerian and Lagrangian formulations of the condition of radial equilibrium, the plastic zone solution can be eventually obtained by solving a system of eight partial differential equations with the three stress components, three anisotropic hardening parameters, specific volume, and preconsolidation pressure being the basic unknowns. Parametric studies have then been conducted to explore the influences of $$ K_{0} $$ consolidation anisotropy on the stress patterns outside the cavity, and on the stress path for a soil element at the cavity wall.

This paper presents an investigation of the remoulding effect on the compression behaviour of artificially structured clays. The compressibility of structured and remoulded clays can be divided into two stages: pre-yield regime and post-yield regime. After the remoulding process, the compression curves of remoulded clays lie below those of artificially structured clays. The variation in compression characteristics of cement-stabilized clays is quantitatively discussed based on the laboratory tests. The results demonstrate that the artificial remoulding, closely related to the destructuration, causes an important decrease in yield stress, compression index and an increase in recompression index. The post-yield compression curves of artificially structured clays and remoulded clays can be well normalized by Burland’s void index. However, the normalized post-yield compression curves of remoulded clays agree well with Burland’s ICL, but an obvious divergence from Burland’s ICL can be found for the normalized curves of artificially structured clays since the high consolidation stress exceeds about 2000 kPa.

The fractional-order plastic flow rule for monotonic loading condition is generalized in this study by analytical derivation to consider the loading and unloading behavior of granular soil under triaxial compression and extension conditions. An improved fractional-order plasticity model is then proposed by using the generalized fractional-order plastic flow rule. The proposed model is validated by simulating a series of experimental results of different granular soils subjected to monotonic and cyclic loading conditions. It is found that unlike the previous model, the proposed model is capable of simulating different kinds of material deformation under monotonic and cyclic loads.

The ultimate bearing capacity of a rigid strip footing on a soil slope is significant for practical engineering on the slope. Based on the upper bound theorem of kinematical limit analysis, an analytical solution to the ultimate bearing capacity is obtained and calibrated from laboratory model test results. The results obtained using the proposed method are in strong association with those calculated using classical methods. To further ascertain the validity of the theoretical method, a numerical simulation is performed to analyze specific examples. The theoretical results are fairly identical with the numerical results. All these comparisons between the analytical and the numerical or laboratory results demonstrate that the proposed method is acceptable. On this basis, the effect of parameters on the bearing capacity, such as footing width, horizontal setback distance of the footing from the edge of the slope, the dip angle of the setback segment, the dip angle of the slope face, the internal friction angle, cohesion, the unit weight of the soil, and the embedded depth of the footing, are investigated. The calculated results show that the ultimate bearing capacity decreases with the increase in the slope dip angle and the dip angle of the setback segment, but increases with increases in the other parameters.

Of a great interest for loess is the wide distribution over the seismic region in China and it is vulnerable to seismic-hazard under the earthquake loads. Evaluation and understanding the dynamic properties of loess is therefore a matter of concern at both academic and practical levels. This paper presents results from a series of cyclic triaxial tests on loess samples that were obtained from two boreholes of different depths at Lingshi County in Shanxi Province, in which the characteristics of shear modulus (G) and damping ratio (D) were both examined. It was found that the shear modulus decreases with void ratio, yet the influence becomes less profound at a higher shear strain level. As compared with the water content, the changes of shear modulus yield a better correlation with the void ratio. Besides, the normalized shear modulus (G/G 0 ) and the damping ratio (D) of loess were also examined. At the same shear strain level, the modulus reduction curve of loess is higher than that of sand, while under otherwise similar conditions the damping ratio of loess becomes lower.

The interface shear strength between a soil nail and the surrounding soil is required for the design analysis and safety assessment of a soil nailed structure, such as a slope, retaining wall or excavation. It has been found that a number of factors may influence the interface shear strength, such as the normal stress, soil properties, soil nail surface roughness, degree of saturation, and grouting pressure. Firstly, this paper introduces a laboratory soil nail pullout box with full instrumentation and special devices for controlling the degree of water saturation, pressure grouting, and the setup of this box. Secondly, the paper describes the test procedures and a programme for studying the influence of over-burden pressure, degree of water saturation, pressure grouting. The paper presents representative test results. The influences of over-burden pressure, degree of water saturation, grouting pressure on the pullout resistance of soil nails are examined and discussed. From the test results, relationships between pullout resistance, over-burden pressure, degree of water saturation, and grouting pressure are obtained and discussed. In general, the over-burden pressure has little influence on the pullout resistance, the increase of degree of water saturation will reduce the pullout resistance. Grouting pressure will increases the pullout resistance. The increase may be more evident when the over-burden pressure is larger due to confinement. Pressure grouting is a cost effective method for increasing the soil nail pullout resistance, thus, improving the performance of the nailed structure.

Soil nailing is a widely used ground stabilization technique utilizing the nail to retain soil mass, especially the cut and fill slopes. Since pull-out resistance is vital to the working capacity in field practice, so the study in enhancing the pull-out resistance is enormous. In this study, a series of model tests were conducted for the compaction grouted soil nail of single grout bulk, the results of which were compared to that of the 3D finite element method simulations. Since more grout bulks generate higher pull-out resistance, further finite element method simulations were conducted for the soil nails of double grout bulks of different diameter and spacing. However, due to the earlier appearance of failure for the soil nail of double grout bulks, the failure pull-out displacement was studied. The result shows, with the increase in diameter for the grout bulks, the failure pull-out displacement is decreased. In addition, the larger spacing is benefit to enlarge the failure pull-out displacement, however, the influence from the spacing enlargement is more significant to the soil nail of smaller grout bulk.

With the rapid development of the economy in the southwest China, more and more large projects are built in such areas. However, how to fill and cut well has been frequent problem because the western region is mostly mountainous areas. Especially for filling, in order to protect the stability of constructions, mechanical properties of granular materials used to fill are quite important. Particle size distribution, fines content and characteristic particle size values are main factors that affects mechanical properties. Under different confining pressure, the changes in fine particle content can lead to change granular materials’ mechanical properties. In this study, three sets of granular materials with different fine particle contents (PSD-1: 20%, PSD-2: 30%, PSD-3: 40%) and three samples (fine particle content of 20%) with different characteristic particle size values are considered. Simulation results indicate that the mechanical properties of granular materials are better when fines content is 40% under low confining pressure. However, when confining pressure is more than 400 kPa, mechanical property of granular materials with fines content of 20% is better.

The foundations supporting the high and heavy storage tanks at an alumina refinery plant experienced extremely large settlements and the normal operations of the tanks have been affected. To find the reasons for the unexpected large settlements of the foundations, the original design was reviewed and the soil compression properties used for calculating the foundation settlement was checked. It was found that the compression index values used in the original design were too small and the effect of sample disturbance on the compression index was not considered when using the laboratory consolidation test results. By using the Schmertmann correction procedure to consider the effect of soil disturbance, new compression index values were determined. The corrected compression index values were used to calculate the settlements of the foundations and the predictions were in good agreement with the field settlement measurements. This study further indicates the importance of considering the effect of sample disturbance in the determination of soil compression index values using laboratory consolidation tests.

Ultimate shaft resistance had relation with the cohesive strength between the soil and pile surface. On the other hand, when shaft resistance was large enough and the stress combination in soil around a pile satisfied Coulomb’s law, the soil would be in shear failure state and could not bear more loads. This showed that shaft resistance played at such time would also be considered as ultimate shaft resistance. Hence, ultimate shaft resistance had relation with both cohesive strength and the stress state of the soil. Hence, a method for calculating ultimate shaft resistance was put forward when it was controlled by the stress state. The working stages for a bored pile in service were divided as construction, service and maintenance and the characters of additional stresses caused by subsurface friction in soils in each stage were analyzed, based on which, the calculation of compression module of soils during different working stages were set up. Thus, the influence of the additional stress mentioned above on the changing of compression module of soils and on the transformation of τ~s curve during different working stages were discussed together and it was deduced that how to decide the increase ratio of the bearing capacity of a pile in a bridge after the pier and superstructure of the bridge strengthened or rebuilt to its initial one in normal service stage after it was bored. The amend factors for side resistance of soils around a pile with stable settlement were put forward, which finally forms the evaluation method for subsurface friction of soils around a bridge pile in service on the basis of the additional stress in the soils.

Strength measurement of surficial sediments was crucial for deep-sea developments. Compared with piezocone test and vane shear test, the full-flow penetrometers (T-bar and ball) could better estimate the undrained shear strength of extremely soft deep-sea surficial sediments. In this study, high-quality samples were recovered from three interesting sites in the west of South China Sea using box corer, and a newly developed miniature full-flow penetrometer was introduced and utilized for measuring the penetration resistances of sediments. Combined with vane shear strength data and empirical equations, the intact and remoulded undrained shear strength, strength factors and soil sensitivity of sediments was obtained and discussed. The results also proved that the performance of the new miniature full-flow penetrometer was reliable and effective.

Piled embankments are applied to deal with soft foundation in the high speed railway engineering. In that case, load transmission usually occurs by soil arching effect in piled embankments. In the model test of this passage, a jack fixed with different active plates were used to control the pile-and-soil relative displacement combined with PIV. The results about the development of sliding surface shape and the failure angles in different filling heights and pile spacing in soil arching effect were displayed. It can be found the shape of sliding areas on the top embankment is relevant to embankment height and pile spacing. Initial failure angles were determined by the filling height and finally close to 90°. The equal settlement plate increased with the increasing of pile-and-soil relative displacement linearly when the top of embankment was not effected by differential settlement.

The engineering design of underground protective structures subjected to blast loading requires an appropriate stress-strain relationship for surrounding geomaterials. The behaviour of geomaterials under blast loading depends upon strain rate, stress level and interaction among the three phases. A few advanced constitutive models are proposed in the literature to model stress-strain behavior. However, a less accurate but simple alternative is to use functional forms for capturing the experimental stress-strain curves. In this paper, the functional form of stress-strain curve of geomaterials subjected to air-blast (uniaxial high strain-rate loading) is proposed based on the deformation mechanism of geomaterials. The proposed model consists of two different expressions for loading and unloading and requires only three parameters. The physical meaning of the three model parameters is discussed and the procedure for their evaluation is outlined. It is found that the proposed functional form captures the experimental stress-strain curves very well.

The effect of overlying soil load around deeply buried piles is not considered in current uplift pile analyses of deformation and bearing capacity. To this end, we proposed a deformation compatibility nonlinear analysis model by taking overlying soil load into consideration and obtained load-displacement relationship of piles subjected to this load. Moreover, we experimentally obtained load-displacement curves of tension piles under different levels of overlying soil load. Both theoretical and experimental results showed (1) the initial pile displacement increases with overlying soil load increasing; (2) overlying soil load improves pile’s ability to resist uplift and reduce their deformation and failure; and (3) disregarding the presence of soil overlying load would lead to overestimation of pile body deformation and underestimation of uplift resistance. Our results prove that the new model can better reflect the actual pile-soil interaction and provides a new method for analyzing the actual working performance of tension piles. It is necessary to take the effect of overlying soil on peri-pile into consideration in practice.

Consolidation of porous media under self-weight is a common process in nature environment and engineering facilities, such as sedimentation of soil particles in river delta and the consolidation of mine tailings during operation of tailings reservoir. During self-weight consolidation, the excess pore pressure is a typical indicator for degree of consolidation. In this study, a one-dimensional (1D) model coupling the nonlinear variation of hydraulic conductivity and compressibility was proposed to simulate the self-weight consolidation process. Because of the nonlinear variation of soil parameters, a nonzero excess pore pressure was formed at steady state, and an iterative method was employed to obtain the distribution of the ultimate excess pore pressure along the model height. The results of the iterative method was then verified by the results from numerical simulation. The magnitude of the ultimate excess pore pressure induced by the nonlinear soil properties could be significant and should be adequately considered in engineering practice.

This paper describes an investigation into the effect of fabric anisotropy on the phase transformation (PT) behavior of granular soil by a DEM (discrete element method) analysis. The results indicate that the PT behavior of granular soil depends on fabric anisotropy created in the particle deposition process. As the deviation of principal anisotropy direction of soil fabric from the loading direction escalates, the mean effective and deviatoric stresses decrease, with the PT behavior being more easily developed. At a microscopic level, fabric anisotropy relating to both contact and particle orientations is found not to be a suitable micromechanical indicator of macroscopic PT behavior, while the occurrence of PT behavior is accompanied by the emergence of local minimum coordination number (or mean contact normal force). Furthermore, the PT line in e c – log pʹ plane is revealed to be non-unique, and fabric anisotropy is a fundamental factor affecting the position of PT line in e c – log pʹ plane.

Deep cement mixing is widely used to improve soft soil deposits consisting of peat or clay in many regions of the world. Although deep mixing is a well-developed technology, mechanical properties of Deep Cement Mixed (DCM) soils show large variability within the geometric space. The coefficients of variation of the DCM soil strength range from 0.3 to 0.8 according to the literature. In the conventional design practice, DCM column improved embankments are designed assuming uniform column strength. Factor of safety (FOS) is introduced to the design to avoid any risk associated with uncertainty of strength properties. However, the performance of a column improved embankment with uniform strength properties can be different from the performance of an embankment with the same mean strength but varying strength properties across the column geometry. High variability in DCM column strength will lead to large differential settlements, non-symmetric behavior of the embankment and local failure within the columns. Having a good understanding about the significance of variability on the embankment performance, will allow the designers to improve the reliability of DCM column-supported embankments, systematically. As an initiation to the variability dependent performance analysis, this study investigates the reliability of a DCM column improved embankment considering the variability of strength properties among individual columns. Strength properties within columns were assumed as uniform in this study. Analysis was carried out for a range of coefficients of variation and mean strengths. Monte Carlo simulations were used to determine the probability of unsatisfactory performance. Results show that the reliability levels of the embankment increases with increasing partial factor of safety (PFOS) for strength, which is the ratio of mean DCM strength to deterministic design strength and decreasing coefficient of variation (COV). The values of PFOS and COV that give acceptable performance levels were also investigated. However, further analysis should be conducted considering the spatial variability of strength properties within individual columns, to confirm these observations.

Three-dimensional numerical modelling based on the finite difference or finite element method used in solving geotechnical problems, which involve soil consolidation and complex material models, require large amount of computer memory and computational time. Alternatively, simplified numerical models of three-dimensional geotechnical problems can be used to predict the performance, while achieving high analysis efficiency. When simplified modelling of a column-supported embankment is concerned, two-dimensional plane-strain models can be easily adopted since an embankment is a relatively long structure compared to its width. Different methods have proposed in the literature, to convert a column-supported embankment into a two-dimensional plane-strain model. Some of the popular two-dimensional idealization methods are; conversion based on equivalent properties (EP) and conversion based on equivalent area (EA). However, no study has investigated the suitability of these simplified models to analyze deep cement mixed (DCM) column improved embankments, where yielding of DCM columns is of concern. The post yield softening behavior of DCM columns affects the load transfer mechanism and consolidation behavior. Therefore, a simplified model that can capture this behavior should be selected carefully to obtain reliable results. This study investigates the performance of a DCM column improved embankment, which experienced post yield softening behavior, using two-dimensional plane-strain models simplified based on EP and EA approaches. The numerical models were developed using ABAQUS/standard finite element program. Strain softening behavior of the DCM soil was incorporated using a special material model, which is an extended version of the Mohr Coulomb failure criterion. The simplified model results were compared with the field measured data in terms of settlements, lateral deformations and pore water pressures. The results demonstrate that the final predictions were significantly varied between the two idealization techniques.

Solutions for cavity contraction are used widely in tunnel engineering but rarely in bored pile foundation which is a three dimensional problem. Traditional cavity contraction theory are based on the isotropic initial stress supposition (i.e. the lateral pressure coefficient K 0 = 1.0). However, the K 0 of the soil is not equal to 1.0 actually. In this paper, based on the Mohr-Coulomb yield criterion and the associated flow rule, the analytic solution for stress and displacement fields of borehole contraction considering K 0 was deduced. The relationship between the initial borehole radius a, the contracted radius a 0 , the plastic zone II radius r p and the internal pressure p is also analyzed, result shows that the a 0 is a function of a, r p and p. In addition, using the curves of the plastic zone radius and the stress fields versus borehole depth, the influence of the internal pressure p and the lateral pressure coefficient K 0 , and the internal friction angle ϕ are discussed. It shows that p and ϕ have great influence on the plastic zone radius and the borehole wall stress, while the effect of K0 on the borehole wall stress is limited and mainly focuses on the upright part of the borehole. It can be illustrated that traditional solutions based on the assumption of K 0 = 1.0 underestimated the plastic zone field while overestimated the stress around the cavity. Moreover, it should be noted that the effect of r p on the stress and displacement around borehole is non-negligible. This paper consummates the borehole contraction in bored pile foundation.

This paper focuses on the settlement of loess high-fill ground. The settlement characteristics of the loess filled ground in the gully were studied by centrifuge model tests. The results indicate that those factors, i.e. the boundary condition, fill height, valley shape, compaction degree, and humidification, have significant effect on the settlement of filled ground. Settlement occurs mainly in the construction stage, and the post-construction settlement linearly increases with increasing filled height. The narrow valley tectonic has obvious deformation confinement effect on the filled soil. The full compaction of filled loess during the construction phase can reduce the post-construction settlement, and the improvement of compaction degree will be more obvious for the settlement control of large thickness filled ground. Due to the water-sensitive characteristics of loess, a significant settlement caused by wetting exists as long as the filling material being humidified, even though the post-construction settlement tends to be stable.

One of the special design issues for the immersed tunnel is the stability problem of the structure under wave impact with significant wave height. A better understanding of the wave–seabed-structure interactions is essential for the evaluation of the stability of the seabed foundation under dynamic loading in the ocean environments. However, too much attention was paid on the characteristics of wave loading in most previous numerical models. Few investigations have been conducted for the cyclic behavior of the seabed deposits. In this study, based on Biot’s partly dynamic poroelastic theory, a viscoelastic constitutive model in terms of Davidenkov backbone curve was used to describe nonlinear stress-strain hysteresis characteristic of the seabed soil. The pore pressure increasing pattern is modeled by Byrne pore pressure increment model, which was introduced as the wave-induced residual pore pressure source term, and implanted into Biot dynamic consolidation equation. Then, an effective stress analysis framework was established and used to analyze the dynamic response of a shallow buried immersed tunnel. The results indicate the high efficiency of the proposed analysis method to capture the complex wave–seabed-structure interaction and the relevant design issues are discussed as well.

Liquefaction in undrained soils coincides with the development of significant excess pore water pressures. The undrained behaviour of soils has been studied extensively using laboratory testing, but these tests cannot give any insight into the micromechanical changes that cause the observed macro-scale response. One way to obtain insight into the micromechanical behaviour is to use a suitable numerical technique such as the discrete element method (DEM). The ‘constant volume’ method, in which the sample volume is maintained constant throughout shearing, is often used to simulate the undrained test condition. In this method the soil sample is assumed to be perfectly saturated with an incompressible liquid. The constant volume method has the advantage of computational simplicity. However, some problems arise when simulating dense samples such as the generation of unrealistically high stresses and excessively large interparticle overlaps. There is a clear need to develop an alternative to constant volume simulations which retains the method’s computational efficiency but without the unphysicality. In this paper, several reasons are proposed for the inability of constant volume simulations to quantitatively capture a real soil’s undrained behaviour. Alternatives to the constant volume method are discussed, all of which allow the sample volume to vary during the simulation by incorporating the effect of pore pressure. One method was selected and implemented in the open-source LAMMPS DEM code, and its appropriateness for simulating undrained soil behaviour is explored with reference to monotonic simulations of sand.

The stress-dilatancy relationship could guide and form the basis for the development of a constitutive model for polypropylene fiber-reinforced soils. Fiber reinforcement presents a promising alternative in the projects involving either localized repair of slopes or reinforcement of thin soil veneers, especially when the planar reinforcement (e.g., with geotextiles and geogrids) is difficult to implement. However, the existing stress-dilatancy theory has not been evaluated for discrete fiber reinforced soils. In this study, a number of triaxial compression tests were carried out to investigate the effectiveness of randomly distributed fiber reinforcements on the stress dilatancy of Nanjing sand. A new parameter representing the increase in the effective confining stress was introduced to describe the stress-dilatancy of fiber-reinforced sand. To consider the fiber reinforcement, a new stress-dilatancy relationship was proposed for fiber reinforced sand based on Rowe’s stress-dilatancy for granular materials. The stress-dilatancy relationship is validated against a series of triaxial tests on Nanjing sand and Hostun RF sand mixed with discrete polypropylene fibers.

This paper investigates the bearing capacity of ring footings under eccentric load by using the simplified method as well as numerical simulations. In the simplified method or effective area method, it is assumed that the ring footing is equivalent to a rectangle with the same area, which is under uniform pressure and the corresponding bearing capacity is estimated by traditional bearing capacity equation. The soil is assumed to be cohesionless. By using three-dimensional simulations, the bearing capacity of ring footings with eccentric load is assessed too. The results are compared with each other in terms of Reduction Factor (Rf). This factor is the ratio of the bearing capacity of an eccentrically-loaded footing to that with centric load, which is a function of load eccentricity. As the load eccentricity increases, the bearing capacity decreases. Comparison of the results shows that the simplified method underestimates the bearing capacity of eccentrically-loaded ring footings.

Based on the transformed stress and the subloading surface concept, a new generalised critical state model with special focus on the volume change under general loading conditions, is presented in this paper. As existing test date show that not only the shear strength, but also the volume change of clays depend on the loading conditions, a new stress-dilatancy equation defined in the transformed stress space is established. Compare with the Cam-clay model, the proposed model only adds two new parameters. The proposed model can not only describe the strain-softening behavior of overconsolidated clays, but also takes into account the influence of intermediate principal stress on strength and deformation of clays.

In this paper, a framework that combines the stochastic multi-objective optimization (MOOP) and the observed field data for identifying soil parameters is presented. For conducting the parameter identification, a multi-objective differential evolution algorithm is employed. Then, an elastoplastic soil model accounting for the small-strain stiffness and anisotropic elasticity behaviors of clays is developed and adopted. Finally, the proposed procedure is applied to a well-instrumented deep excavation. The observed wall deflection and ground settlement are used as objective in the optimization. The results demonstrate that the anisotropy of elasticity and small strain stiffness are two important factors influencing the ground settlement and wall deflection in the excavation. All the comparisons demonstrate that the proposed framework is effective and efficient for identifying soil parameters from excavation.

The vacuum preloading method combined PVDs has been widely used to improve the engineering properties of dredged marine clay. Comparing with the surcharge preloading method, the vacuum preloading method has no stability problems. However, it is found in the field test that the improved soil still has further settlement after unloading the vacuum pressure. To investigate the mechanism of the vacuum preloading process, series of triaxial tests were conducted to simulate the vacuum preloading process for dredged clay. The compressibility of the clay under different stress paths was measured. It is found in this paper that the deformation of dredged clay after unloading of the vacuum pressure includes two parts: one is the elastic deformation caused by the unloaded instant soil, and the other is the plastic shear deformation produced by the soil under the partial stress state. When partial stress keeps constant, the larger stress ratio induces larger deformation.

A total of 54 groups of direct shear tests are carried out on the interface between concrete and clay to study the interface shear behaviors by using large-scale interfacial direct shear apparatus. The effect of unloading and roughness on the mechanical properties of the interface are discussed. The results show that the interface initial shear modulus and shear strength increases with the interface roughness R for the same residual load ratio η, and there exists an optimal residual load ratio ηb that corresponding with the maximum value of the relative growth rate of shear strength. The effect of unloading and interface roughness on the interface residual ratio of shear strength f r is limited when the value of η is larger than the critical residual load ratio η cs . However, the value of f r increases with the η when the value of η is less than η cs . At last, the shear dilatancy phenomenon is observed during the unloading process, while the strain-softening phenomenon is not be found in the experiment, and the maximum value of shear dilatancy presents a positive relationship with the interface roughness for the same residual load ratio η.

The loess-mudstone interface landslide is one kind of the loess landslides with special characteristics, such as continuous and low-rated deformation. Because of the relatively lower rate of deformation before the landslide initiated, the damage of this kind of landslides is always irreparable. In order to investigate the mechanism of loess-mudstone interface landslide and provide better controlling measures, triaxial tests and ring shear tests on the slip surface were carried out. It is aimed to analyze the shear strength characteristics of slip surface. Eight groups of consolidated undrained triaxial tests and five groups of consolidated drained ring shear tests were set. As the slip surface consisted of loess and weathered mudstone which is different from normal ones mostly containing the same material, there must be differences of shear strength characteristics between them. The results of the tests showed that the stress-strain curves of triaxial tests of the slip surface were significant strain-hardening, and the shear strength of slip surface is higher than that of pure loess but lower than the pure mudstone. The shear strength of the slip surface in ring shear tests increases with the growth of normal pressure. However, the shear stress of multistage ring shear test is much larger than the value of single-stage ring shear test. In conclusion, shear strength characteristics of slip surface in loess-mudstone interface landslide showed that this kind of landslides moved slowly but continuously. The stability of slip surface would be enhanced if the groundwater was prevented in time.

In order to obtain expansive soil strength parameters in accordance with engineering practice, an experimental research was carried out by simulating the process of dry-wet cycle on undisturbed expansive soils obtained from the “Yin Jiang Ji Huai” project. The analysis focused on the effects of dry-wet cycling times, dewetting temperature and cyclic amplitude on the expansive soil. It is shown that the dry-wet cycling times, dewetting temperature and cyclic amplitude can all attenuate the shear strength of expansive soils. With the increase of dry-wet cycling times, the shear strength decreased gradually and finally reaches a constant state. The shear strength decreased with the increase of the dewetting temperature and the cyclic amplitude. In comparison, the dewetting temperature had a greater effect on the shear strength stability of the soil. The results show the significance of combining engineering practice with experimental research for shear strength stability of expansive soils to select the cycle amplitude and dewetting temperature which are consistent with practice besides the dry-wet cycling times. Only by this way can we select the appropriate strength parameters for stability analysis

When a pile is pushed into the ground, it will incur displacement field in the ambient soils which will pose danger to existing structures, e.g. pipelines, foundations, and tunnels. To characterize the soil displacements caused by press-in piles, model tests combined with digital image correlation (DIC) techniques were performed. A digital camera was installed outside the model box to measure the full-field displacements. In addition to soil displacements, eight earth pressure sensors were installed to investigate soil stress in the horizontal direction during the whole process of pile installation. Based on model test results, it was found that both soil stresses and displacements in the horizontal initiated and peaked before pile tip approached. When pile tip passed the designated depths, the soil stresses went back to initial at-rest state and soil horizontal displacements stabilized. In general, soil displacements and stresses were conjugated behaviors during pile penetration. However, the conjugated relation at 3D (D is the width of model pile) distance from pile surface was less pronounced than 1D.

A series of ring shear tests of sandy silt landslide slip soils in the Upper Jinsha River was conducted under different normal stresses and shear velocities. These tests were aimed at exploring the shearing mechanical properties of the soils. The relation between shear stress and shear displacement and the peak softening and strength variation of the samples were analysed. Results show that the fluctuating extents of the relation between the shear stress and shear displacement of the samples vary under different velocities and normal stresses. The degree of post-peak softening of the sample is low when the shear velocity is rapid, and the normal stress is large.

Mica particle has numerous flakes foliated over each other which cause elastic/resilient nature. The inter-particle contacts between fragile/weak platy mica particle and hard spherical sand particles in micaceous sand would result in complex sand-mica particle assemblies such as bridging, ordering and pore filling. The regular arrangement of sand above mica particle (ordering) and irregular arrangement of sand below mica particle (bridging) would create large void spaces in micaceous sand. The essential problem of micaceous sand is the low shear strength and high resilient nature due to large void spaces, which substantially varies with drainage and loading conditions. The current study investigates the effect of loading (compression & extension) and drainage (undrained & drained) conditions on stress-strain and volumetric response of micaceous sand. The influence of variation in particle arrangement of sand-mica and mica-mica contacts (bridging, ordering & pore filling) and the resilient nature of platy mica particle on shear behavior of micaceous sand were also analyzed under varying boundary conditions. The impact of such influences on shear behavior of micaceous sand was observed to be greater in undrained and compression testing conditions as compared to drained and extension testing conditions respectively.

The discrete element method (DEM) plays an import role in the study of the constitutive relationship of granular materials by providing multi-scale data. It serves as an effective tool for numerical experiments, which however need to be conducted with care. The sample generated and tested in DEM is considered a representative volume element, which hence should be uniform. However, when loaded with frictional wall boundaries, as required to impose in-plane surface traction with controllable loading directions, arching develops near the corner. This paper addresses the effectiveness of using polyhedral specimens to reduce the arching-induced sample non-uniformity when running DEM numerical experiments to study the loading path dependence of granular materials. The previously proposed algorithm in Li et al. [1] has been implemented in the open-sourced software LIGGGHTS. Observations on the contact forces show that the samples become more uniform as the polyhedral specimen approaches a sphere. This study confirms the necessity of using polyhedral specimen shape when reproducing the elementary behaviour of granular materials subjected to varying loading directions.

The three-dimensional finite element method is employed to study the static and dynamic behavior of an asphalt-concrete core rockfill dam. The results show that the distribution of the stress and deformation of the asphalt-concrete core at the completion stage and during the operating period is reasonable and the core won’t experience shear failure. Second, the vertical stress within the impervious core is higher than the upstream hydrostatic pressure, and hydraulic fracture is thought to be impossible. Third, under earthquake loading, an obvious whipping effect can be seen at the crest of the dam. The higher the input earthquake acceleration peak is, the larger the value of the maximum acceleration response of the dam body will be. The distribution of the maximum dynamic displacement of the dam is similar to that of the maximum acceleration response. In addition, under earthquake loading, the shear strength of the asphalt-concrete core is higher than the shear stress of the core, meaning that shear failure will neither occur in the core under dynamic loading. Through the systemic research on the static and dynamic behavior of the asphalt-concrete core dam, it can be obtained that the impervious system of the dam is good at the completion and impounding stages and the stress and the deformation behaviors of the dam are also good under earthquake loading. The results also show that better joining forms of the dam core and the impervious wall are put forward through optimization design to improve the stress deformation at this part and guarantee the safety of the dam body.

This study presents centrifuge model test results of the stress and deformation characteristics of earth retaining structures with sloping backfill and local loading. Transducers are used to measure the horizontal force, bending moment and lateral displacement of the wall during the test. Silty sand is selected as backfill soil. Lateral earth pressure distribution along the wall and structure deformation are continuously measured. Test results indicate that the front wall exhibit a rotation about the top movement mode and the lateral earth pressure acting on the front wall cannot be calculated via conventional theoretical methods. In addition, lateral force increases nonlinearly with depth. This effect is more evident at the lower part of the front wall, which causes the point of the application of total thrust to occur at relatively low locations. A simplified calculation method that considers wall displacement is introduced to provide a good description of lateral earth pressure and its distribution along the wall in the height direction.

Foundations on subsoil of many properly designed caisson breakwaters, in the last several decades, have collapsed or suffered severe damage. Many geotechnical failure modes may take place. In order to have a good knowledge of this problem, it is necessary to study the effect of subsoil properties and the possible failure modes during wave attack in the stability analysis of caisson breakwater. Traditionally, the stability analysis is performed in a too simplistic way, by assuming the subsoil to be single layer and linear elastic. In this paper, the foundation is modeled as multi-layer soil and presents elasto-plastic behavior. By using the geotechnical software FLAC3D, the effect of surface soil properties and the failure modes of caisson breakwaters under the excitation of wave loads are discussed.It is concluded that the caisson breakwater constructed on soft soil tends overturned failure mode, and the rotation center is 1/8 caisson width positive away from the middle point along the bottom edges. Moreover, the anti-overturning capacity increases with stiffer surface soil. Those results can provide a theoretical basis for the practical design of caisson breakwater.

Based on the laboratory tests of shanghai remolded silty clays, the effects with different concentrations of contaminations (HCl, H2SO4, NaOH) on soil plasticity, compressibility and strength characteristics were studied. The results shown that the value of the liquid limit wL, plastic limit wP, plasticity index IP, void ratio e, compression index cc and undrained shear strength cu were all increased with the increasing of concentrations of H2SO4 and NaOH. However, the contrary relationship was obtained for the HCl contaminated soil samples except the compression index cc. All of these phenomena can be explained by the ion-exchange, PH value and soil structure. The relationship between mechanical properties and plasticity parameters (cc~wL and cc~IP) of the contaminated soil samples were presented and compared with the empirical formulas for remolded clays, the results shown that the empirical formulas will underestimate the compressibility of the contaminated soil samples. However, the change of contaminated soil samples structure is not sufficient to change the relationship between cu and liquidity index IL, so the empirical formulas for remolded clay can be approximately predicted the relationship of cu and IL of these contaminated soil samples.

A series of laboratory experiments were conducted to study the change in the engineering geological properties of diesel-contaminated soil. Soil samples with different contaminant concentrations were manually prepared via mixing and static compaction methods. The influence of diesel contamination on engineering properties of the soil was analyzed from the perspective of granulometric composition, Atterberg limits and indices, mechanical properties and microstructural features, and its mechanism of action was discussed. The results showed that contaminated soil contained more fine particles, and a sample with 8% diesel had the highest clay content. With increasing contamination, the plastic limit decreased slightly; the liquid limit increased initially and reached its peak value at 8% diesel content and thereafter decreased slightly. The sample with 4% diesel content had a higher unconfined compression strength than the uncontaminated sample and other contaminated samples. The microstructure changed from an aggregated fabric into a dispersed fabric after the addition of diesel, decreasing the strength of soil.

This paper describes a numerical investigation on the effect of inter-particle friction on the shear behavior of granular materials, with an emphasis placed on an energy-based analysis. The numerical simulation results show that the peak friction angle $$ \phi_{p} $$ increases with the inter-particle friction angle $$ \phi_{\mu } $$ , and that the constant-volume friction angle $$ \phi_{cv} $$ increases with $$ \phi_{\mu } $$ in the low friction region before reaching a plateau stage at the high friction region, with the division point of such two characteristic stages emerging between $$ \mu_{s} $$ = 0.3 and $$ \mu_{s} = 0.5 $$ . The energy-based analyses indicate that inter-particle friction exerts a profound effect on the energy dissipation and storing of granular assemblies. The inter-particle friction behavior and damping mechanism are the two major means in the consumption of the external work input. Frictional dissipation increases at first with the inter-particle friction coefficient in the low friction region, and then decreases in the high friction region, with the damping consumption exhibiting a reverse variation manner. The mobilized shear strength depends primarily on the energy stored in the normal direction at the contacts, E pn , which demonstrates the same variation mode as the deviatoric stress and constant-volume friction angle, despite that the energy stored in the tangential direction at the contacts, E pt , as well as the mobilized friction coefficient $$ \mu_{b} $$ , shows a monotonic increase with the inter-particle friction coefficient.

The loose media slope is a special kind of rock slope which have characteristic of high intensity, usually accumulated by earthquakes. Substances of the loose slope have some properties, such as nonlinear, non-homogeneous and non-continuous. However, in the southwest of China, the frequent incidence of earthquake makes the problem of stability for loose media slopes prominent.In this paper, particle flow code (PFC) was applied to effectively simulate the loose media slope which is located in Ya-Kang highway of MK0+455 according to the analysis of field investigation. Results show that the progressive failure process of loose media slope under seismic loading is consists of three main aspects. First is the process of loose and landslide that happened in the accumulation layer. Second, some loose rocks fractured during this process because of collision and friction. Third, bond failure and crack development that happened inside the loose media slope. Furthermore, the result found that the bond failure process and crack development process have remarkable spatial and temporal characteristics. Obviously, the motion is weakened inside the loose media slope especially when rocks sliding after seismic loading.

Filtration of grout is a common phenomenon during dispersion. It may cause the blocking the injection process thereby reducing the effectiveness of pile reinforcement. The sphere dispersion model considering filtration was analyzed to study the radial distribution of grout concentration. Based on the analysis results, numerical model of grouted pile foundation were constructed using PFC to study the influence of filtration on bearing capacity. The results show that the grout concentration decreases gradually during dispersion. The reinforcement effect of the grout on the end capacity of the pile is gradually weakened due to the filtration. The bearing capacity of the grouted pile decreases with the increasing filtration coefficient. Based on the traditional theory of grout diffusion without considering the filtration, the bearing capacity of pile may be overestimated. Filtration test should be carried out to evaluate the injectability of the grout before the design of grouted pile foundation.

Surface surcharge is regarded to be one of the main factors that will cause large deformation of tunnel. On the other hand, it is widely accepted that the soil exhibits significant spatial variability that consequently causes the large variation of structural performance of embedded tunnels. This paper aims to investigate the influence of soil vertical spatial variability on tunnel subjected to the surface surcharge. Herein, the random finite difference method (RFDM) is used. Random fields of elastic modulus E s of soils are generated and mapped into finite difference analysis to reveal the impact of spatial variability. Given the modeling specifics mentioned above, some results of the numerical simulations are found: (1) the spatial variability may be underestimated if the discretized points in simulating the vertical random field are too coarse; (2) there exists two critical scale of fluctuation: 15 m and 10 m for COV of E s at 0.15 and 0.35 when evaluating the crown settlement. The estimated value will be high if neglecting spatial variability; (3) the run number for Monte Carlo simulation (MCS) also plays an important role; a converged run number means that the COV of generated data is not sensitive to the run number. In this study, it is about 300 in this sense; (4) the different combination of scale of fluctuation and limiting value will lead to wide range difference when evaluating the probability of exceedance and reliability index. Therefore, it is necessary to consider the spatial variability on analyzing the effect of surface surcharge on tunnel.

In view of the fact that the molecular dynamics (MD) method is similar to the discrete element method (DEM), which is suitable to model granular material and to observe the trajectory characteristic of a single particle, so to possibly identify its dynamical properties. A set of laboratory model tests of sand granular flow was performed, during which the configurations of sand granular flow were captured by the monitoring system. Thereafter the MD approach was used to study the three-dimensional gravity-driven granular flow of sand in a model box inclined at 0°. In addition, the simulated sand granular flow behavior was compared with previous experimental results, which showed a high degree of similarity. This indicated that the MD method can accurately represent the evolution of the sand granular flow. Finally, it was proposed that the MD method probably can be applied for predicting the flow properties of various soil flow problems.

The world-famous Large Hadron Collider (LHC) particle accelerator is housed about 100 m below ground surface in a large-scale underground tunnel network at the European Centre for Nuclear Research (CERN). Miles of deep CERN tunnels were excavated decades ago lined with spray shotcrete in a weak sedimentary rock called the red molasse, which is a rock mass comprising an irregular, alternating sequence of sandstones and marls. Such complex ground conditions have contributed to significant bending moment in the tunnel lining and consequently led to cracks, water infiltration and other structural distress years after tunnel construction. In this paper, a series of soil-fluid coupled finite element (FE) analysis was conducted to investigate the long-term behaviour of a CERN Tunnel: TT10 in the molasse region. For simplicity, the tunnel behaviour was investigated in a 2D plane strain condition at a representative horseshoe shape cross section. The complex ground strata were modelled using 8-node quadratic elements with local mesh refinement, whilst engineering properties of different layers of sandstones and marls were considered with a particular interest in ground permeabilities. Results show the development of pore water pressure with time around the tunnel when the tunnel lining is fully permeable acting as a water drainage channel. Furthermore, the long-term tunnel deformation is detected to be within only several millimeters. The computed FE results show a decrease in the horizontal diameter accompanied by an increase of the vertical one, suggesting a vertical tunnel elongation mechanism of deformation, which was also confirmed by the data collected from field measurements.

The swelling characteristics of bentonite play a very important role in ensuring the long-term stability and isolation of high-level radioactive waste (HLW) repositories. A custom-made test apparatus, capable of providing a range of boundary conditions, was designed to investigate the swelling behavior of bentonite. The imposed boundary conditions include constant mean stress (CMS), constant volume (CV) and an intermediate flexible boundary condition called constant stiffness (CS), which applies stress as a specified function of volume increase. The results show that boundary conditions significantly affect the swelling strain and swelling pressure of the bentonite tested. More specifically, the relationship between the range of boundary conditions provided and the corresponding swelling pressures are: CV > CS > CMS, while the relationship between the range of boundary conditions and the corresponding swelling strain is CMS > CS > CV. Based on these results, several swelling equilibrium limit (SEL) curves are developed to index the effect of boundary conditions on soil swelling potential. The methodology can be used to predict the final stress and volume states of bentonite during fluid infiltration under the range of boundary conditions possible in HLW repositories.

The understanding of internal response of particle dislocations is vital to clarify the progressive failure in granular materials. This paper proposes a non-destructive testing method, Acoustic Emission (AE) technology, to characterize the mechanical behavior associated with particle-to-particle sliding and asperity/particle breakage in sand subjected to drained-triaxial compression. Particle dislocations during compression is accompanied by a sudden release of stored strain energy, which could be detected by AE sensors and characterized as elastic waves with different frequency properties. Insights into the correlations of stress-strain and frequency response of AE activities in terms of total, high frequency and low frequency AE event rates are offered, demonstrating that the mechanical behavior of particle dislocations and soil density could be highly characterized by AE activities. Besides, particle dislocations associated with particle-to-particle sliding and asperity/particle breakage is distinguished by high frequency and low frequency AE activities. The result suggested that the frequency response of AE activities is closely related to the failure mode, degree and rate of sand particle dislocations under drained triaxial compression. This technology seems promising as an alternative means to clarify the inter-particle mechanism during progressive failure in sand.

Cyclic plastic strain behavior of unbound granular materials (UGMs) exhibits significant stress path dependency. Using a customized triaxial apparatus capable of applying stress path loading, a series of laboratory repeated load triaxial (RLT) tests were conducted on two typical UGMs through simultaneously varying the axial stress and the radial stress. Effects of realistic in-situ stress paths due to a passing wheel on cyclic plastic strain behavior of unbound granular base and subbase materials were investigated and quantified. The analysis of experimental results revealed that the accumulated plastic strain responses of both UGMs subjected to different stress path loadings can be described by the shakedown approach. The shakedown ranges of different stress path loads were classified for both materials. Finally, the significance of the findings made in pavement design practices was highlighted to evaluate permanent deformation resistance of UGMs and their suitability for use in pavement foundation layers.

To investigate the dynamic resilient modulus of lime soil, and find out the law of resilient modulus decay under freeze-thaw cycle, adapting to the new design code and maintenance system of highway subgrade in China, a series of dynamic tests were carried out according to the standard laboratory test methods (JTG D30-2015). The effect of freeze-thaw cycles on the dynamic resilient modulus of lime soil was investigated and analyzed. Experimental test results show that for lime-treated soil, with increasing freeze-thaw cycles, dynamic modulus reduces about 0.0–46.4%. Then, compared dynamic modulus of clean soil, finding that lime has satisfactory reinforcement effect.

The trapdoor test is a widely employed experimental method to investigate the change of the stress distribution on engineering structure caused by the tunnel excavation in tunnel engineering. In this paper, the trapdoor tests for cemented soils with different cohesions were simulated with the Distinct Element Method (DEM), where the effects of cohesion on the failure mode and the earth pressure on the trapdoor were presented and the measured results were compared with experimental data. The results show that the DEM simulation can provide numerical results similar to the experimental data, such as the failure mode and earth pressure distribution. The soil fails at the end of the test with the damage zone, shear band and the influential zone formed in the ground. The earth pressure on the trapdoor decreases to a minimum value firstly and then increases to a constant value with the lowering of the trapdoor. The range of influential zone and the minimum earth on the trapdoor decreases with the increase of cohesion.

Silos and storage tanks are filled and emptied periodically in operational period, which leads to the ground soil underneath these structures experiencing the long-term and low-frequency cyclic loading. Series of undrained triaxial tests were conducted on the intact Shanghai soft clay retrieved from a construction site at Pudong area. Monotonic load and cyclic load with low-frequency were applied to investigate the development of pore water pressure and accumulated axial strain in the test specimens.Test results illustrate that the stress-strain (σ − ε) shows lightly softening characteristics, and the behavior is more pronounced, especially in the case of a higher confining pressure. The variation of axial strain ε a is similar to that of permanent strain ε p under different cyclic stress ratios, and the accumulated axial strain is not only related to the CSR, but also to the effective confining pressure and the deviator stress levels. the resilient modulus decreases with the increase of CSR. Compared with high-frequency cycle loading, the soft clay exhibits plastic deformation in advanced during low-frequency cycle loading. The normalized residual excess pore pressure is equilibrated fast with the decrease of effective confining pressure. The normalized residual excess pore pressure is almost equal at the different deviator stress levels. The experimental results show that the development of pore water pressure is a time dependent phenomenon, independent of frequency.

Multistage slope is widely used in the immersed tube tunnel foundation trench slope scheme, a reasonable slope scheme need to consider both security and economy. On the background of an immersed tube tunnel foundation trench slope design in Guangzhou, impact factors like slope stages, slope ratio and slope platform width on stability of this multistage slope are analyzed, the strength reduction method is adopted for stability calculation by FEM software. A reasonable foundation trench slope scheme is obtained and the instability calculation result is presented. In addition, effect on the slope stability when a metro tunnel under-crossing the foundation trench slope is proved to be small.

Sand is the most widely existing granular material for the foundations of extensive constructions which bear various complex cyclic loading such as traffic loading, ocean wave loading and earthquakes. The road pavements and the offshore foundations subjected to cyclic loads tend to produce excessive permanent deformation, which affects the constructions’ normal operation and safety. Nowadays, many engineering projects change from strength controlled criterion to deformation controlled criterion, such as the high-speed railway in China. Therefore, accurately prediction of the settlement due to cyclic loading is essential. Over the years many explicit models have been established to predict the permanent deformation of sand under cyclic loading. Most of these models are more or less empirical and lack of essential analysis of permanent deformation. There are many parameters obtained by fitting the test results in these models which cannot be easily determined in practical engineering use. In this paper, the concept of shear strain amplitude during cyclic loading is put forward to predict the permanent deformation. By introducing the shear strain amplitude, a unified explicit model is established to predict the cyclic permanent deformation of sand, which only contains four empirical parameters. The result shows that the model can successfully predict the permanent deformation under cyclic loading.

Sandstone, limestone, slate with the diameter of 50 mm are used to simulate ball-ball contact of coarse-grained soil under the joint action of normal and tangential force by employing Rock Rheological Testing System. Breakage modes of particles, Elastic Core, tangential force-displacement curve are occupied to analyze the influence of breakage characteristics of particles by considering the material properties and the normal force percentage. Through the experimental study, it was discovered that contact point was eroded under the normal force, and the failures of particles depended on normal and tangential force. Particles were easier to break into more pieces and quality ratio was closer to 1 under larger normal force percentage. The top area and the depth of Elastic Core is proportional to the normal force percentage. For every 10% increase in normal force, the tangential force and tangential displacement are reduced by 20% and 10%, respectively. The tangential stiffness increases linearly with the normal force percentage. This paper studies particle breakage characteristics of coarse-grained soil from particle contact perspective, which lights up a new way to study the particle breakage of coarse-grained soil, and can also be expected to provide contact mechanical parameters for discrete element numerical simulation.

Nowadays, expansive or swelling soils considered as a worldwide issue which poses several challenges to geotechnical engineers. Expansive soils are classified as a high-plasticity fine grained soils which mainly consists of clay minerals. This paper is intended to investigate the expansive soils characterizations along Tabriz Northern Highway (TNH) and their destructive effects. TNH with length of 17 km is constructed about 10 years ago. Geology formation of TNH and its around is consisted of different layers of mudstone, marlstone, and sandstone. The expansive soils formation is result of weathering of these rock layers. There are some challenges for TNH pavement such as: longitudinal and transverse fractures and cracks, the distortion and settlement of surface which is cause many accidents. Field studies are shown that the main reasons of TNH pavement problems are soil swelling and settlement of fill soils below pavement. For investigation of swelling characterization of soils, some samples were obtained and tested in laboratory. The test results indicate that the unified classifications of soils are mostly CL and clay material of soils is about 30%. Plasticity index of soils is placed between 7 and 23%. Swelling potential of soils along TNH is evaluated low to medium. In order to ground treatment, soil-cement is placed under road using the local soil material.

A 3D multi-scale approach is presented to investigate the mechanical behavior of a macroscopic specimen consisting of a granular assembly, as a boundary value problem. The core of this approach is a multiscale coupling, wherein the finite element method is used to solve a boundary value problem and a micromechanically-based model is employed to build the micro constitutive relationship used at a representative volume element scale. This approach provides a convenient way to link the macroscopic observations with intrinsic microscopic mechanisms. The drained triaxial test under the plane-strain condition is selected to simulate the occurrence of strain localization. A system of shear band naturally appears in a homogeneous setting specimen. The normalized second order work is introduced as an indicator in order to predict the unstable trend of the system.

Granular material is a typical multi-scale material, which physical and mechanical properties are similar to continuous medium in macroscopic scale, but discontinuous and strongly anisotropic in micro- and meso-scale. In this paper, numerical simulations of biaxial tests for ideal granular samples with different initial densities were carried out using discrete element method (DEM). Loop structures, which are represented by voronoi polygons, were taken as the basic meso-mechanical unit of granular material by mesh-subdivision. The evolutions of numbers, geometrical morphology for different loops were simulated and analyzed. From the mesoscopic point of view, critical state of granular media is the consequence of mutual transformation for higher-order loops and lower-order loops, the combined average and external manifestation of all loops.

Soil arching is one of the most universal phenomena in the geotechnical engineering practices, such as embankment, tunneling, piping, and retaining wall. In the past decades, most studies mainly focused on soil arching under static loading. However, some numerical studies and field tests show that soil arching more likely degrades to failure under cyclic loading than under static loading. In this study, a series of two dimensional (2-D) trapdoor tests with transparent soil were carried out to investigate the soil arching phenomena under cyclic footing loading. The test setup included a container with inside dimensions of 90 cm (length) × 10 cm (width) × 50 cm (height) and three trapdoors with 20 cm in length installed on the base of the container. A cyclic surface footing load was applied at the center of the transparent soil. The Particle Image Velocimetry (PIV) technique was adopted to investigate the deformation field in the transparent soil. Three influence factors (fill height, load frequency, and geosynthetic reinforcement) on the soil arching phenomena under cyclic footing load were explored. The test results showed that the increase of cyclic load frequency accelerated soil arch failure. The inclusion of geosynthetic reinforcement enhanced the stability of soil arching under a cyclic footing load. The existence of soil arching redistributed displacements in the fill. After the soil arching was destroyed under the footing load, the displacements in the fill spread out in a similar manner with that in the model test without trapdoor movement.

In order to establish a geometric model of loess microstructure, three-dimensional reconstruction of pore size, shape and spatial distribution in loess is carried out. Firstly, undisturbed loess in Jingyang is scanned by industrial CT, then the scanned two-dimensional section CT images are extracted by threshold to separate the pores. The three-dimensional pore model of loess is established. Based on the three-dimensional pore model, a simple sphere joined with a strip is used instead of the complicated pores in the loess. Then the pore size distribution curve is drawn and pore center line equation is fitted by using the center coordinates and radius of sphere. Results show that: the section images of loess can be obtained by industrial CT. Via 3D reconstruction techniques, three-dimensional model in different directions and different part of undisturbed loess can be obtained. It is easy to measure the size and direction of pores by using spheres instead of complicated pore forms in undisturbed loess, reducing quantitative analysis of pore morphological characteristics. The method presented in this paper can provide a basis for quantitative statistical analysis and pore morphology analysis.

Particle size distribution (grading) and particle shape are two of the most salient factors that affect the mechanical behavior of a granular material. In this paper, a machine learning and level set-based method is proposed to obtain the particle size distribution and three-dimensional particle shape information of a granular Martian regolith simulant from its X-ray computed tomography (CT) images. The extracted realistic particle shapes are characterized by various shape descriptors and are then incorporated into the development of a shape and grading-dependent three dimensional discrete element model. Numerical repose angle tests are conducted to demonstrate the capability of the DEM model and to study the mechanical behavior of the Martian regolith simulant. Validated against conventional laboratory tests, the numerical analysis provides insights of the material behavior from the fundamental level.

Based on 2D discrete element software PFC2D, a centrifuge test of dry sand under dynamic compaction was simulated using the sample of the same grain composition. On the basis of the physical and mechanical parameters of foundation soil in the centrifuge test, the microscopic parameters of particles were obtained through a simulated biaxial test. The settlements of tamping pit in the numerical simulation were in good agreement with the results of the centrifuge test and the field test, which proved the validity of the numerical simulation. The results show that all the time curves of dynamic stress in the soil present a single peak, which accords with actual situation. When soil mass becomes stable, the porosity is smaller than the initial one and the coordination number of particles is bigger than the initial one, therefore the soil mass after tamping becomes denser. With the increase of tamping times, the total depth of tamping pit increases, however, the settlement value each tamping decreases. The study on the microscopic characteristics of soil is helpful to grasp the process of soil compaction and guide foundation treatment of dynamic compaction.

Aggregates of coarse grains are commonly used in earthworks. Their deformation parameters are usually extrapolated from experimental data obtained from finer materials with scaled grading. To ultimately achieve a rational and robust extrapolation law, this study employs the distinct element method to investigate the grading effect on the deformation modulus of coarse aggregates. Triaxial compression tests are simulated on a set of specimens with different grain size distribution (GSD). The relations are examined between the deformation modulus and the shape coefficients of GSD curve, coordination number, and volume weighted coordination number. The results show that the mechanical coordination number is insufficient to determine the deformation modulus under a wide range of GSD. Instead, regardless of variation in GSD, a unique correlation is found between the deformation modulus and the volume weighted coordination number, which can be estimated from the effective void ratio.

Rockfill materials are widely used in constructions, such as rockfill dams, railroads and embankments. However, the mechanical behavior of rockfill materials is difficult to investigate in laboratory due to the limited size of apparatus. In addition, the microstructural characteristics of rockfill materials under loading is difficult to observe in laboratory experiments. In this study, the scale effect on the macroscopic and microscopic mechanical behavior of rockfill materials was investigated by the discrete element method (DEM). The parallel gradation technique and the mixed technique, were used to reduce the maximum grain size of the prototype gradation (60 mm) to that of the scaled gradation (20 mm). The mechanical behavior of scaled DEM samples was obtained from a series of conventional triaxial compression tests. The results show that the strength of rockfill materials with the same maximum grain size was affected by different modeling techniques in DEM.

In this paper, a numerical investigation on the collapse of axisymmetric granular columns has been conducted using three-dimensional discrete element method. Three different initial particle shapes are considered in simulations. The final deposit morphologies for different initial conditions are compared each other in terms of final height and run-out distance, and also compared to experimental observations. It can be concluded that granular column with more elongated particle shapes can reduce the angular velocities of particles, arise the final height and reduce the run-out distance by comparing to pure spherical particles.

Micromechanics-based model have proved to be efficient in describing the mechanical behaviour of granular soils with few physical meaning parameters. Among these models, a family of micromechanical models was constructed based on the static approach that is a bridge connecting micro forces and macro stress. This paper presents the application of a static hypothesis based CH micromechanical model to solve boundary value problems (BVPs) using an implicit integration method. The model was first calibrated by results of elementary tests of Hostun sand and then was implemented into a finite element code. Two typical boundary value problems: a biaxial test and a square footing were numerically analysed to demonstrate how the micromechanical model can be applied to multiscale modelling of geotechnical structures.

In this study, 40 groups of normal contact tests under the ball-surface contact condition between the marble spherical samples and the marble cuboid samples were carried out by use of the rock rheological testing system, in which marble spherical samples were used to simulate coarse grained soil particles. The compression breakage laws and mechanical mechanism of the single coarse grained soil particle was obtained by researching failure mode, the broken process and mechanical property of the samples by means of statistical methods. Then, in order to observe the development of this process, the particle contact numerical model was established and a numerical simulation was carried out with PFC3D. Based on the experiment results, it was found that, at the beginning of loading, the coarse grained soil particle was partly broken at the contact point due to stress concentration, and an elastic core was developed after that; then, the increasing of normal contact force caused cracks near the elastic core; finally, crack transfixion occurred and the particle was totally broken. Having observed the broken particles, it was found that elastic cores of which the top surface was a sub-circular plane and the lower part was a cone appeared in all particles. Moreover, the diameter to depth ratio of the elastic core was close to 2:1. In this research, we provided a new way of study on particle breakage behavior of coarse-grained soil by researching the mechanical mechanism of particle breakage in the perspective of particle contact of coarse-grained soil.

It is difficult to accurately simulate the deformation and failure process of accumulation slope because of its inherent discontinuity, in-homogeneity and aeolotropism properties. Discrete element method (DEM) is adopted in this paper for preliminary study of the deformation and failure process of accumulation slope. Strength reduction method is introduced into the DEM for the study of slope safety factor and the critical slip surfaces; the whole progressive failure process of accumulation slope is also investigated from a microscopic view. Particle friction coefficient and bond strength are set as variables in the process of strength reduction in PFC. Cumulative displacement of slope crest and slope toe and numerical results of particle unbalance force are recognized as a comprehensive index of slope failure. The failure process and safety factor of accumulation slope are obtained by DEM simulation. For comparison, limit equilibrium method (LEM) and finite element method (FEM) are used for the same example. The results show that discrete element strength reduction method outstands in the study of discontinuous medium. The progressive failure mechanism of the accumulation slope is revealed. The safety factor obtained by sole use of DEM is basically the same with that obtained by combined use of FEM and LEM, indicating the safety factor obtained is reliable.

Measurements of shear/compression wave velocity by bender/extender elements are closely associated with the elastic properties of granular soils. Generated by point sources, the wave differs with the propagation directions. To examine the wave propagation anisotropy, mono-sized spheres structured in face-centered cubic packing were generated and bender/extender element tests were simulated using discrete element method. Isotropic and anisotropic consolidations were conducted during the modeling. Meanwhile, by changing the geometry and relative location of the transmitters and the receivers, the required directions of wave propagating and particles vibrating were achieved. Based on previous techniques to avoid near-field effects and determine wave arrival time, the responses of receivers were recorded and analyzed. Static loading simulations were carried out to obtain the small strain stiffness at a small strain level. A general consistency of static loading results and wave velocities measurements shows that continuum assumption for elastic wave in granular materials is reasonable. Since fabric anisotropy is eliminated in regular packing structure, the contribution made by contact normal force is same as prediction. The revelation of micromechanics of wave propagation stands as a solid proof that wave propagation depends on the soil state.

A stochastic micromechanical framework is presented to predict the probabilistic behavior of saturated concrete repaired by the electrochemical deposition method (EDM). The repaired concrete is represented as a multiphase composite composed of the intrinsic concrete, water and deposition products. Multi-level homogenization schemes are presented to predict the properties of the repaired concrete. The equivalent inclusion is reached by homogenization of the two-phase composite composed of the deposition products and the water. The equivalent composite of the repaired concrete is attained by the homogenization of the two-phase composited made up of the equivalent inclusion and the intrinsic concrete. By modeling the volume fractions and the properties of constituents as stochastic, the deterministic framework is extended to stochastic to incorporate the inherent randomness of the effective properties among the different specimens. Through the Monte Carlo simulations, the probabilistic behaviors are obtained, such as the mean, the different order moments and the probability density functions. Numerical examples including deterministic and stochastic micromechanical validations indicate that the proposed models are capable of providing an accurate framework in characterizing the effective properties of the concrete repaired by the EDM.

Interactions between continuums and granular materials are common phenomenon in engineering applications, and in numerical simulation the coupling of the finite element method and discrete element method may be the best method. In this study, a sophisticated algorithm of sphere-facet contact algorithm is developed for the interaction between finite element method domain and discrete element method domain. Base on the coupling algorithm, a coupling engine of two open source computer codes is developed, where YADE for the discrete element method and OOFEM for finite element method. Two classical verification problems are used to explore issues encountered when coupled finite-discrete element method, namely, the efficiency of the engine, the influence of the element size and the mechanical parameters of the contacting interfaces. All the numerical results indicated that coupling finite-discrete element method developed in this study can better descript the interaction between the solid and the granular material.

Silica sands are known to exhibit a time-dependent response to applied loads, particularly after they were disturbed, for example, due to compaction. This behavior was documented by a time-dependent increase in shear wave velocity in sand subjected to sustained loads. The change of material properties with increasing time is often referred to as sand aging. While several hypotheses have been proposed to explain the aging process, none has been generally accepted by the research community. The hypothesis advocated in this paper is that static fatigue at contacts between the grains may be a key factor in time-dependent behavior of silica sand. An apparatus was constructed to load individual sand grains, and the time-dependent deflection under sustained load was monitored. The rate of deflection was found dependent chiefly on the surface texture of the grains (roughness), with rougher surfaces at contacts being more susceptible to larger deflection. The process of static fatigue occurring at the contacts is also referred to in this presentation as contact maturing. The results of grain scale testing in the custom-constructed apparatus are consistent with the hypothesis, which implies that contact maturing is a plausible contributor to aging of silica sand.

The miniature penetrometer tests are often used to investigate the distribution and strength of aggregates in soils. In this work, the elastoplastic solution to spherical cavity expansion for stress distribution in saturated clay is studied using the cavity expansion theory in combination with the modified Cambridge clay (MCC) model. From the case study, it can be found that the radial stress, circumferential stress and tip resistance increased when the modulus of compression increased. The radial stress increased nonlinearly when the critical stress ratio increased. However, the relationship between circumferential stress, tip resistance and critical stress ratio showed linear growth properties. When the penetration probe diameters are in the range of 1.75 to 2.95 mm, theoretical values are smaller than test data, and all the deviations between theoretical and test values are within 5%. Therefore, results indicate the elastoplastic solution can be used to predict the tip resistance and penetration stress.

More generally, the clay specimen is regarded as the homogeneous body in the process of numerical analysis. In effect, the clay is heterogeneity. Aim to study the evolution features of shear stresses and rotation angles of major principal stresses at out of shear band during early loading state based on clay actual mesostructures using the Duncan-Chang theory, the actual mesostructures were taken into consideration when the clay numerical model was constructed. Through the microscope, the original image which included the clay skeleton and the pores before loading was captured. Then, the Otsu’s method was used to convert the image captured into the binary one for identifying the exact boundaries between the skeleton and the pores. The binary image, in which white areas were called the skeleton while the black ones were the pores, was transformed into the vector diagram which was the input document for the finite element software. So, the 2D model with clay actual mesostructures was established based on the vector-graph. Meanwhile, the model parameters used in the 2D model were given by the triaxial compression test. Then, the numerical analysis was performed for simulating the unconfined compressive test. The results show that the actual model can not only reveal the evolution features of internal shear stresses and rotation angles of major principal stresses at “points” located in skeleton from the mesoscopic but also depict the evolution curves of Mises stresses along the paths.

The Discrete Element Method (DEM) has been widely adopted in investigating many complex geotechnical related problems due to its capabilities of incorporating the discontinuous nature of granular materials. DEM can be very effective when simulating soil encountering large deformation or distortion (e.g. cavity expansion) since other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly in problems concerning in-situ testing, pile installation, underground excavation, deep foundations, to name a few, explaining why cavity expansion simulation using DEM is worthy to be conducted. Although many discrete element numerical studies have been carried out to investigate the problems associated with granular materials, there are very limited findings reported regarding the effects of particle size scaling. Therefore, in this study, a series of three-dimensional numerical models with different size scaling factors have been developed using PFC3D software, developed based on DEM. It should be noted that the numerical model has been calibrated for medium sandy soil adopting the experimental results obtained from the triaxial test in drained condition. To examine the effects of particle-scaling during cavity expansion, several cylindrical cavities were created and expanded gradually from an initial radius to a final radius, while stress variations, volumetric changes, as well as radial movements of gauge particles were monitored during the entire simulation. Furthermore, the internal cavity was loaded using a constant strain rate, while the outer boundary was automatically controlled through a servo mechanism to maintain a constant external pressure adopting appropriate subroutines. Cavity pressure variations, stress-strain responses and radial displacement of gauge particles obtained from different simulations were discussed and compared. It is observed that the particle scaling factor beyond a certain limit can affect the soil response during cavity expansion.

Rock Particle Flow Code (PFC) model has numerous micro parameters, and its quantitative determination is completed by try and error, which consumes a large amount of time and efforts of researchers. Under this background, the quantitative determination approach of rock micro parameters is of significant importance. This study proposes a simplified model based on PFC2D to analyze the stress mechanism from the perspectives of force balance and deformation equilibrium, and explores the theoretical relation between macro tensile strength and micro parameters. The direct tensile test is simulated by PFC2D to explore the influence of contact normal bond strength (micro tensile strength) σcn, particle size (maximum particle diameter Dmax, and particle diameter ratio Dmax/Dmin) and normal to shear stiffness ratio kn/ks on macro tensile strength. Based on the results of theoretical analysis and statistical analysis, the quantitative determination approach of micro tensile strength in direct tension test is determined.

A coarser soil structure resulted from fines loss may lead to change in hydraulic and mechanical properties which can cause significant settlement or failure of the levees, embankments and dams. This paper investigates mechanical consequence of gradation change induced by removal of finer particles in sand-gravel mixtures. Discrete Element Method (DEM) is used to conduct numerical triaxial tests of soils with prescribed loss of finer particles. A network-science based community detection method is used to characterize the force-chain networks of the soil samples under loading before and after loss of different amount of finer particles. A “community” refers to a set of particles which are closely connected with strong forces. The communities in a force-chain network can be detected by analyzing the inter-particle contact force data. Such communities can be quantified using intrinsic parameters such as community size (total number of particles in the community), strength (the total contact forces in the community), and morphology (the shape of the community). It is noticed that the effect of fines removal depends on the “size gap” between coarse particle and fines. Insights into the micro-mechanism can be gained from comparing the community parameters.

The investigation of granular flows is of great significance to industrial production, e.g., rotary dryers, ball mills and mixing drums, as well as the prevention of natural disasters, e.g., landslides, mudslides and avalanches. The rotating cylinder model is capable to capture the macro characteristics of granular flowing modes transition in laboratory tests, which is the most classic experimental method to study granular flows. However, it is difficult to observe the micro characteristics on granular flowing motions in physical model tests. Therefore, the Distinct Element Method (DEM) is employed to study the motion mode of particles in cylinders with focus on the gravity effect in this study. The results show that DEM has an obvious advantage in simulating granular flows tests with the contact model considering rolling and twisting resistances. The dynamic angle of repose increases with the gravity level, which implies that motion mode of particles evolves from the slumping motion to the rolling motion. Moreover, the maximum velocity of the particles flow increase with the gravity level. But when the gravity level is larger than 1 g, the maximum velocity of the particles increases slowly.

A moving object on a surface slows down and eventually rests where there is no energy input to the object. In physics, the changes in state are caused by the surface asperity existed between the object and the surface, dissipating kinetic energy of the object. This interpretation is simply summative and does not reflect many micromechanics details associated with the object motion. This paper presents a study on the micromechanics of a single particle travelling on a rugged surface. The micromechanics look into the particle-surface contacting, and resulted energy dissipation of the particle. A discrete element model is developed to mimic the contacting. This model is validated against analytical exact solutions which are developed in terms of Newton’s laws of motion. This study examines some important physical conditions on the contacting and the energy dissipation. An interesting example problem is examined to provide results gained from the two approaches. This research is fundamental in that it re-defines inter-particle friction from the micro-scale perspective. Therefore the research helps predict any particle-based geo-motions, e.g. particles piling, debris flow, and rock falls.

Investigation on thermal properties of Shanghai soft clay is of great importance for the design of subway fire safety in Shanghai. Using the heat probe method, thermal conductivity tests were conducted on the remolded specimens of the silty clays from the ④ and ⑤−1 layers in Shanghai. Results show that the thermal conductivity of saturated Shanghai soft soil decreases with the increase of void ratio. For given void ratios, the thermal conductivity of saturated Shanghai soft clay increases with increasing temperature, while the increasing rate depends on the temperature. For constant void ratio, with increasing water content, the thermal conductivity of Shanghai clay increases first and then turns to decrease with a maximum value appearing close to the water content corresponding to the plasticity limit of the soil tested. This observation may be due to the shrinkage of the specimen, which induces the decrease of the void ratio resulting in closer contact of soil particles.

The variation of soil mechanical properties during the freeze-thaw cycles, especially the reduction of air suction in the thaw stages, was investigated in this paper. The reduction of air suction is the major cause of the volume expansion between 20–50 min during the thaw stage. An innovative TDR tube sensor was developed to nondestructively monitor the freeze-thaw process, from which the water content and the degree of freeze-thaw can be accurately determined. Compared with existing technologies for frost measurement, TDR has advantages in that it provides more details on the progresses of freeze-thaw status. With the assistance of this tool, not only the onset of freeze or thaw process, but also the extents of their development can be investigated. From the measured soil mechanical properties, an analysis is given to calculate the change of air suction during the thaw stage. The air suction at complete thaw status can be measured by use of a traditional instrument, such as a tensiometer. As a result, the air suction pressure during the thaw process can be indirectly measured.