Skip to main content
main-content
Top

About this book

This volume gathers the latest advances, innovations, and applications in the field of geotechnical engineering, as presented by leading researchers and engineers at the 7th Italian National Congress of Geotechnical Researchers (CNRIG 2019), entitled “Geotechnical Research for the Protection and Development of the Territory” (Lecco, Italy, July 3-5, 2019). The congress is intended to promote exchanges on the role of geotechnical research and its findings regarding the protection against natural hazards, design criteria for structures and infrastructures, and the definition of sustainable development strategies. The contributions cover a diverse range of topics, including infrastructural challenges, underground space utilization, and sustainable construction in problematic soils and situations, as well as geo-environmental aspects such as landfills, environmental and energy geotechnics, geotechnical monitoring, and risk assessment and mitigation. Selected by means of a rigorous peer-review process, they will spur novel research directions and foster future multidisciplinary collaborations.

Table of Contents

Frontmatter

Protection

Frontmatter

Influence of Numerosity and Distribution of Piezometric Data on the Performance of a Warning Model for Weather-Induced Landslides in Norway

Territorial landslide early warning systems (Te-LEWS) are widely applied worldwide to deal with weather-induced landslides over wide areas, typically through the prediction and forecasting of meteorological parameters. However, meteorological monitoring alone does not allow to take into account critical soil conditions controlling the triggering process. Depending on local conditions, landslides may be triggered in response to a large variety of weather events. Therefore, the integration of geotechnical monitoring data within warning models for weather-induced landslides at regional scale can provide supplemental information useful to determine the likelihood of a given weather event actually producing landslides.A methodology designed to integrate widespread meteorological monitoring and pore water pressure measurements is herein applied within 30 hydrological basins highly susceptible to weather-induced landslides in Norway. The correctness of the predictions in relation to different network configurations of the piezometers is evaluated through a series of parametric analyses. The results of a first application of the proposed warning model are also presented and discussed. This study should be considered as a first attempt to define the conditions for adopting an economically sustainable and technically reliable geotechnical monitoring strategy for predicting the conditions leading to the triggering of weather-induced landslides over wide areas.

G. Pecoraro, M. Calvello

Temporal Evolution of the Force Exerted by Dry Granular Masses Impacting on Rigid Sheltering Structures

In this paper, the Discrete Element approach is employed to study the evolution with time of the impact force exerted by dry granular flows on rigid obstacles and to better understand the impact mechanism. The dry granular mass is initially positioned in front of the wall with an assigned uniform velocity and porosity and the evolution with time of the impact force is evaluated. In particular, the influence of both mass initial porosity and front inclination on the impact force evolution has been investigated. From a design point of view, the results integrate the formula that was previously introduced by the authors for the maximum impact force, by adding information about its time evolution.

I. Redaelli, C. di Prisco, F. Calvetti

Planning and Monitoring of Mitigation Measures in a Landslide-Affected Area Through Numerical Modelling, Conventional and Satellite Data

Pisciotta village, located in the Southern part of Cilento, Vallo di Diano and Alburni National Park (Campania Region, Italy), is strongly affected by erosional and gravitational phenomena which cause severe damage to existing structures and infrastructures. In this paper, we describe the approach adopted to design and monitor stabilization interventions carried out on unstable sectors of the village. The preliminary geological and geomorphological characterization of the phenomena has led to plan a site-specific geotechnical investigations and monitoring system to assess the stability conditions of the slope. Geotechnical monitoring in pre-intervention phase benefitted of boreholes, successively equipped with piezometers and inclinometers, laboratory testing (triaxial test, shear stress test, etc.) and historical remote sensing data acquired in time-span 2011–2018 by COSMO-SkyMed constellation and processed by means of DInSAR technique have been used to assess the stability conditions. Thus, starting from the defined geotechnical model, a back-analysis slope stability test was performed to assess the safety condition of the slopes, referred to limit equilibrium condition along slip surface. Once validated the geotechnical model in failure condition, remedial works consisting in a drainage system and structural works (bulkhead of poles and retaining walls) have been designed. Finally, the efficacy of remedial works has been investigated by means of DInSAR data analysis. To provide the latter data, a network of passive corner reflectors was designed and deployed within the investigated area, thus obtaining the evolution analysis of post-intervention phase displacement time-series.

Donato Infante, Diego Di Martire, Pierluigi Confuorto, Massimo Ramondini

A Method to Evaluate Debris Flow Triggering and Propagation by Numerical Analyses

Debris flows travel at very rapid to extremely rapid velocity, often involve significant entrainment of soil and occur periodically along gullies and first or second order drainage channels. Owing to their characteristics, these phenomena can cause losses of human lives and significant socio-economic disasters. In weathered gneiss, the analysis of these phenomena is very complex due to the heterogeneity of soils and the difficulty of undisturbed sample taking. On these soils, a preliminary characterization of triggering and propagation phases could be carried out through a debris flow numerical analysis. The paper proposes a methodology for the analysis of a debris flow based on the combined use of two physically based models (TRIGRS and SPH). TRIGRS was used for the analysis of the triggering phase and allowed estimating the mobilized triggering volumes; SPH, using the triggering volumes, allowed the analysis of the propagation phase. The methodology has been applied to a debris flow occurred in Calabria (southern Italy). The obtained results show a good agreement with the real case in terms of both triggering phase, propagation zones as well as of depositional area, and represent the starting point on which to identify debris flow risk mitigation measures.

M. Ciurleo, M. C. Mandaglio, N. Moraci, A. Pitasi

Multi-parameter Vulnerability Analysis of Settlement-Affected Masonry Buildings with Shallow/Piled Foundations: Case Studies in The Netherlands

The paper presents a probabilistic analysis aimed at identifying the most appropriate subsidence related intensity (SRI) parameter (e.g., differential settlement, relative rotation, deflection ratio) that can be used to forecast the severity level of building damage at municipal scale through the generation of empirical fragility and vulnerability curves. The analysis refers to a rich sample of more than seven hundred monitored (by remote sensing techniques) and surveyed masonry buildings – mainly resting with their (shallow or piled) foundations on highly compressible fine-grained “soft soils” – affected by settlements in four urban areas in The Netherlands. The achieved outcomes, once further calibrated and validated, could allow for an improvement of existing geotechnical damage criteria for buildings as well as help local authorities in charge of the management/protection of subsiding urban areas to plan adequate foundation repairing/replacing measures before damage reaches intolerable severity levels.

G. Nicodemo, D. Peduto, M. Korff, S. Ferlisi

Damage to Masonry Buildings Interacting with Slow-Moving Landslides: A Numerical Analysis

This paper presents the results of a numerical analysis aimed at investigating the response – in terms of damage occurrence and development – of a masonry building undergoing settlements induced by a slow-moving landslide. The analysis is performed by applying the Equivalent Frame Method to a model representative of a low-rise building with shallow foundations located in the historic centre of Lungro town (Calabria region, southern Italy). As a main novelty, data collected by way of both conventional (i.e. inclinometers) and innovative (i.e. DInSAR) monitoring techniques are used to derive the three-dimensional settlement trough to be imposed to the building model’s foundation in the numerical analyses. The obtained outcomes are compared with information gathered from multi-temporal damage surveys to the modeled building. Based on previous studies aimed at typifying the slow-moving landslides, the results obtained could concur to the generation of certain building-foundation-landslide typified models helpful for damage forecasting at the municipal scale.

G. Nicodemo, S. Ferlisi, D. Peduto, L. Aceto, G. Gullà

Probabilistic vs. Deterministic Approach in Landslide Triggering Prediction at Large–scale

Reliability in the prediction of rainfall-induced shallow landslides at large scale has constituted a great challenge in the last decades. Different approaches have been adopted to include in the forecasts both the geometric, mechanical and climatic factors that affect the triggering phase of the process. A quite promising one is based on the probabilistic physically–based model implemented in the code PG_TRIGRS, which takes into account the uncertainty in soil spatial variability and characterization. The model uses the Kriging technique to assess the spatial distribution of soil properties for the study areas, starting from available georeferenced measurements, alongwith their probability distribution functions. The Point Estimate Method (PEM) is then used to evaluate the Probability of Failure (PoF) within the study area, where PoF is defined as the probability that the Factor of Safety is less or equal than 1. This version is an extension of the original TRIGRS code, which combines a 1D hydrologic model with a stability analysis to assess the safety level of a given slope in a deterministic manner. In this work we compare the results provided by PG_TRIGRS versus the original version of the code, by applying both of them to the same study area in Central Italy.

Diana Salciarini, Evelina Volpe, Elisabetta Cattoni

Two Control Works to Counteract the Inception of Debris Avalanches

Debris avalanches develop along open slopes, with significant lateral spreading, bed entrainment and flow-like motion associated to large runout distances. Recent numerical methods enhanced the simulation of the inception and propagation mechanisms with reasonable computational times and accurate description of the main kinematic variables such as height and velocity of the mobilised volumes. In this paper, a Smooth Particle Hydrodynamic (SPH) approach is applied to the simulation of propagation scenarios of differently-triggered debris avalanches in presence of two types of engineered slopes. The first option is the installation of a series of baffles in different geometrical combinations; whereas, the second alternative is the implementation of non-erodible zones. Both intervention types are conceived for the hillslope areas, so that the inception of debris avalanche would be limited since the very early stages of the phenomenon. A frictional rheological model is used, and also the role of time-space variable pore water pressures is considered. The discussion of the numerical results focuses on the modifications in the landslide dynamics induced by the two control work options, aimed to discuss the feasibility of such types of interventions in steep slopes prone to debris avalanche triggering and propagation.

S. Cuomo, S. Petrosino

Prediction of Slope Movement Effects on Churches for the Development of a Fragility Curve Approach

Protecting cultural heritage from soil interaction related threats is a current and social issue to which scientific research must offer a contribution, considering also the fragility of the exposed territory. Among the related problems, the aim of this research is to develop fragility curves for churches located in landslide areas, in order to establish a reliable forecasting method applicable to intervention management. The choice of selecting churches as exposed structures makes the theme more challenging for their structural and geometric complexities. To generate the curves, exposed elements and damage severity levels have to be identified, through the definition of an intensity parameter of the landslide effects. The intensity parameter is represented by the global slope safety factor, in order to provide a simple tool to use in engineering practice. Vertical and horizontal slope movements, obtained by numerical analyses, can be related to the relevant safety factors as well as to possible permitted damage levels. The paper reports the proposed methodology applied to a case study, in order to validate the hypothesis of the choice of the safety factor as an appropriate index of intensity.

R. Berardi, L. Cambiaggi

A Simplified Methodology for the Assessment of the Seismic Risk Associated with Small Earth Dams

Small earth dams are characterized by a reduced height of the retaining structure and by a limited reservoir volume. They are often located along slopes close to populated areas, then the risk associated with their potential rupture can be considerable. For this reason, the evaluation of their seismic vulnerability is of paramount importance for Civil Protection purposes. In addition, the usual lack of technical information about these types of dams represents a significant further challenge. In this regards, a simplified methodology based on a reduced number of parameters is required for vulnerability assessment studies. A simplified procedure was developed to systematically classify a high number of small earth dams. The proposed methodology is based on the compilation of data-sheets that lead to a preliminary classification of the earth dams in terms of their associated seismic risk. This procedure was developed within the ReSba project sponsored by the European fund for regional development (Interreg-ALCOTRA) for the French-Italian Alps area. The application of this procedure to more than 100 earth dams in the Piedmont region allowed to identify the most critical structures which require a priority in the planning of further investigations and analyses.

R. M. Cosentini, F. Passeri, S. Foti

Simplified Charts to Evaluate Settlements from Seismic Compression in Dry Loose Sand

In dry loose sand, seismic cyclic loads can result in contractive volumetric strains (seismic densification or compression) that can induce damages to structures, infrastructures and lifelines, accordingly with post-earthquake damages of past events. In the present work, a procedure has been adopted to define simplified charts to predict the possible effect of the seismic compression phenomenon in dry loose sand in terms of soil permanent settlements, to be applied in Seismic Microzonation (SM) studies in the perspective of seismic risk reduction. The adopted procedure estimates the volumetric strains starting from shear strains profiles calculated by parametric 1D site response analyses in which some key-parameters affecting the dry sand behaviour are varied: the relative density and shear wave velocity profile, thickness of the compressible sand layer and its non-linear behaviour, the depth of the seismic bedrock, the input motion amplitude and its frequency content. The proposed charts provide the estimation of settlements in function of the input PGA classes, depth of the compressible sand layer and relative density or, alternatively, shear wave velocity.

S. Fabozzi, A. Porchia, T. Fierro, E. Peronace, A. Pagliaroli, M. Moscatelli

Assessment of Factors Contributing to Levees Stability

The paper focuses on the global instability of levees by analyzing those factors that contribute to the earthwork stability. Moreover, the effectiveness of naturalistic methods is reviewed. Global instability is caused by gravity and seepage forces. Therefore, different collapse mechanisms such as piping, overtopping, hydraulic heave, etc. are not considered. The levee geometry and its hydraulic and mechanical characteristics are the main factors controlling the stability. The material strength, in turn, strongly depends on the degree of saturation, and usually levees are partially saturated. Piezocone tests can be used for a quick evaluation of the effective stress state of partially saturated materials. On the other hand, geoelectric tomography can extend this information from given survey verticals to the whole longitudinal development of the considered levee. Partial saturation strongly contributes to the levee stability and therefore any technique aimed at maintaining the levee under this condition is extremely useful. Protection of the levee - sides by means of geogrids and bio-mats reduces the amount of infiltration water, helps the water adsorption by grass-vegetation and contributes to the mechanical strength thanks to the root-apparatus. The paper provides some preliminary results concerning the contribution of some types of grass to the material strength. The paper mainly shows a possible simplified approach that requires further developments and validation.

D. Lo Presti, S. Stacul, P. P. Capilleri, N. Squeglia

Management of Transport Infrastructures: A Procedure to Assess the Landslide Risk

In recent years, several landslides had a strong impact on the road network, creating the need to define criteria for management and mitigation of hydrogeological risk through landslide zoning correlated with transport infrastructure systems. The reliability of transport infrastructures plays a key role since, in many cases, their inefficiency has caused serious damage to the anthropic system. Recently, advances in cloud computing have opened new opportunities in early warning and emergency management issues. The scientific community has recognized the value of an analytic approach in complex decision making processes for critical situations due to natural events such as landslides. With this aim, the research project CLARA (CLoud platform and smart underground imaging for natural Risk Assessment) has been developed. The objective of the project is the acquisition of local knowledge on issues related to landslide risk that may affect urban areas, through the development of smart technologies that allow acquisition, management and sharing of complex information. The results provide a representation of the consequence analyses induced by landslides with reference to the Sicilian road network in the Enna area (Southern Italy) to be used when planning the mitigation measures to be undertaken in order to improve the prevention and reduction of the disastrous effects of landslides.

V. Lentini, F. Castelli, G. Distefano

Geotechnical Aspects in the Assessment of Stability Conditions of the Volumni Hypogeum in Perugia

Volumni Hypogeum is part of the Palazzone Etruscan necropolis, an archaeological site dated back to Hellenistic period (V sec B.C.). The Hypogeum is a large underground cavity excavated in a partially saturated alluvial soil deposit located in the outskirts of Perugia city. Stability conditions and safety requirements of the vault and the lateral walls are analysed based on the available field results. The physical properties of the material in which the Hypogeum was excavated, such as, natural water content, soil suction, relative humidity of the rooms, temperature, as well as the groundwater conditions undoubtedly influence the state of conservation of the site itself. The variations of these properties may significantly affect the mechanical behaviour of the soil-materials and, in turn, the stability conditions of the ceiling/walls. Moreover, the site is daily exposed to road/rail traffic-induced vibrations. If also considering seismic actions, this site is extremely vulnerable. A multi-scale approach methodology has been recently undertaken aiming at the preservation and protection of the soil/monument system. The present study focuses on a very recent investigation of the microstructural features of the in situ materials. Preliminary numerical analyses of the cave have been performed in order to investigate on the stability conditions.

Manuela Cecconi, Alessia Vecchietti, Vincenzo Pane, Giacomo Russo, Corrado Cencetti

Monitoring of Rain-Induced Landslides for the Territory Protection: The AD-VITAM Project

The authors refer in this paper some of the analyses already done and the planned activities in developing the AD-VITAM Project (InterReg V-A France – Italy – E.U. ALCOTRA), which aims to assess the most suitable techniques to obtain a reliable forecasting of rain-induced landslides, in order to enhance the territorial resilience when subject to such a risk. The authors refers about the procedure called LAMP (Landslides Monitoring and Predicting), consisting in an Integrated Hydrological/Geotechnical numerical model (IHG) fed by site-specific installed sensor-network, to help in the start-up calibration of some of the relevant parameters used by the model. The tuned-up simulation models is used to assess the landslide susceptibility to measured/predicted rainfall histories. The implementation of the numerical geotechnical/hydrological models on a GIS platform with regard to some of the selected sites, and the preliminary tests performed on the sensors to be installed on-site in order to monitor the real-time response to rainfalls are briefly described. Thanks to the effective cooperation with the local technicians and the project partners, the final achievements of AD-VITAM could furnish a real support to a better protection of both the natural and the urbanized environments, allowing site-specific warnings and a better hydro-geological risk management capacity.

Rossella Bovolenta, Roberto Passalacqua, Bianca Federici, Domenico Sguerso

Ground Response Analyses for a Zoned Earth Dam Site in Southern Italy

The evaluation of the performance of critical infrastructure such as earth dams is typically performed using site-specific input ground motions. Input motions can be defined to be consistent with target response spectra derived from probabilistic seismic hazard analyses (PSHA). Such analyses are based on site effects estimated by means of proxies derived from global databases. These site response estimates are called ergodic. The actual site-specific response (non-ergodic) will differ from the global average in a manner proportional to local site complexities. Seismic ground response analyses (GRA) can be used to quantify site-specific effects such as resonance, nonlinear behavior, and impedance. If non-ergodic approaches are used, uncertainties related to site effects can be reduced. In this paper, site-specific ground motions are selected to evaluate the seismic response of a zoned earth dam in southern Italy. Two different target spectra are used: the Uniform Hazard Spectrum (UHS) and the Conditional Spectrum (CS). Differences between these spectra and their effects on site-response are illustrated. Limitations of GRA are also discussed and amplification functions for the foundations of the dam are shown.

Gianluca Regina, Roberto Cairo, Paolo Zimmaro

Digital Terrestrial Stereo-Photogrammetry for Monitoring Landslide Displacements: A Case Study in Recoaro Terme (VI)

Monitoring landslides and potentially unstable areas is of primary importance for the landslide risk assessment and for the identification of the proper mitigation measures. The advanced topographic techniques, such as aerial drone and laser scanner survey, are very good alternatives to the classical survey with total topographic station, because they reconstruct the distribution of surficial displacements with high precision and high resolution. Digital terrestrial photogrammetry and stereo-photogrammetry may represent a low-cost option, which allows long-lasting measurements at fixed time steps. Moreover, at the cost of a lower resolution, it may provide denser distributed measurements on large areas and the reconstruction of the 3D surface of the landslide. Finally, it permits the monitoring of superficial displacements from a temporal sequence of digital images, captured from two or more fixed cameras over a certain period. This paper presents the preliminary results obtained by applying this technique for the displacement monitoring of a landslide close to Recoaro Terme municipality (Vicenza). The setup of the hardware and the procedure of the stereo-photogrammetric method will be briefly introduced. The factors affecting the accuracy and precision of this method will also be discussed.

Lorenzo Brezzi, Fabio Gabrieli, Simonetta Cola, Gloria Lorenzetti, Nicolò Spiezia, Alberto Bisson, Michele Allegrini

Long-Term Monitoring of Landslide Displacements and Damage at Latronico, Italian Apennines

Like many villages of the Italian Apennines, Latronico is constructed on a huge landslide system which causes severe damage to the entire inhabited zone. Continuous reinforcement works, and even demolition and reconstruction of the most damaged structures are continuously being performed, with high social and private costs. This paper presents the results of a long-term monitoring of the displacements carried out by in situ (mobile and fixed-in-place inclinometers and theodolite) and remote sensors (ERS, ENVISAT, COSMO-SkyMed satellites) showing that the landslide system has been moving over the last 25 years with almost constant average yearly rates. The movements in correspondence of the inhabited area occur with rates of several cm/yr along a system of shallow and deep slip surfaces in the range 20 m–40 m depth. The stabilization interventions (shallow and deep drainage, retaining works, reshaping) have had in practice no effects on the general kinematics over the monitoring time. The analysis of the displacement field allows: (a) the localization of the zones of largest deformations and greatest risk for the inhabited area, (b) the identification of the most active triggers and (c) the evaluation of the effects on the displacement rate of the main remedial works.

C. Di Maio, G. Fornaro, D. Gioia, D. Reale, M. Schiattarella, R. Vassallo

Hydrological Characterization of Silty Volcanic Slopes and Physically-Based Early Warning Systems

The paper analyses how rainfall-induced landslide risks may be mitigated by implementing early warning systems in sloping silty volcanic covers. Their answer to rainfall and other atmospheric variables seems to contain features and factors such to provide generality to the topic.The work firstly investigates the factors influencing the hydrological response of a silty volcanic cover referring to results provided by two physical models. Experimental results evidence the importance of accounting for evaporation (or evapotranspiration) and a realistic lowermost boundary condition when the evolution of the hydrological behaviour has to be predicted for early warning purposes. All findings are used to develop a physically-based model suitable for early warning prediction and provide an example of application.

Lucia Coppola, Luca Pagano, Alfredo Reder, Guido Rianna

Analysis of the Effects of Seasonal Pore Pressure Variations on the Slope Stability Through Advanced Numerical Modelling

The paper presents novel results from the advanced numerical modelling of the effect of cycling pore water pressures on landslide processes. It combines the stability analysis of a prototype natural slope through a hydro-mechanical nonlinear finite element approach with the calibration of a kinematic hardening model against representative laboratory data, to draw conclusions of significance to both researchers and designers. The analyses have been carried out for two permanent hydraulic steady-state conditions representing the average pore water pressure regime at the end of the winter and summer season, thus replicating in a simplified way the seasonal fluctuations of the piezometric levels resulting from transient seepage processes generated by the slope-atmosphere interaction. The work shows the ability of the constitutive law, seldom used in these kind of analyses, to predict a progressive accumulation of plastic deformations during the cyclic fluctuation of pore water pressures associated to climate. More importantly, the output of the advanced modelling are useful to support the phenomenological interpretation of the landslide processes associated to natural hazards and to provide guidance for the sustainable management of marginally stable slopes affected by a constant evolution of permanent displacements.

Gaetano Elia, Gaetano Falcone, Federica Cotecchia, Mohamed Rouainia

Displacement Evolution of a Large Landslide in a Highly Fissured Clay

The paper presents an analysis and modelling of the reactivation mechanism of a large landslide caused by rainfall, located in Cerda (Sicily, Italy). The study is based on data collected by means of a field investigation, carried out in order to assess the geotechnical properties of the involved material, and a three-year monitoring programme implemented to measure rain and pore water pressures as well as deep and superficial displacements. Three distinct landslides, evolving at variable rates in different directions, were recognized within the overall landslide area. The data clearly show the mechanical role of pore water pressures in the stability of the slope and point out the dependence of the evolution of displacements on pore water pressure fluctuations. A conceptual and simplified approach is applied to one of the landslides in order to model the time evolution of displacements as a function of pore water pressure on the sliding surface. The model analyses displacement evolution taking into account the viscous forces on the slip surface, assuming infinite slope conditions. The displacements calculated by the model are in good agreement with the measured ones.

Marco Rosone, Maurizio Ziccarelli, Alessio Ferrari

Deep Movements in Clayey Slopes Relating to Climate: Modeling for Early Warning System Design

The current landslide activity in the southern Italian Apennines has been found often prompted by the slope-vegetation-atmosphere interaction, as recognized through both phenomenological and numerical diagnoses in literature. In the very top soil layers this interaction causes transient seepage, resulting in significant variations of pore water pressures with time at both very shallow depths, and at larger depths, below the water table. As consequence, the slope-vegetation-atmosphere interaction often represents the triggering factor of the activity of shallow failure mechanisms, as well as the acceleration of deep slow landslide bodies. In particular, the latter is the case of either structurally complex clayey slopes or slopes location of pre-existing landslide bodies. With reference to the geo-hydro-mechanical context characterizing the south-eastern Italian Apennines, this contribution reports about the numerical investigation of both the pore water pressure and safety factor variations with time across the Pisciolo hill-slope, a representative slope, in relation to the real weather conditions from the 2001 to the 2016. The numerical investigation is aimed at designing an early warning system for the mitigation of the risk related to deep landsliding.

Vito Tagarelli, Federica Cotecchia

A Landslide in Overconsolidated Clays that Has Involved an Important Road of Access to an Internal Mountain Town

The paper presents a case study on the interference of a landslide in overcosolidated clays, triggered in autumn 2004 - winter 2005 by high pore water pressures, on the usability of an important provincial road of an internal town. In the period of 2004–2019 the landslide suffered several mobilisations that led to temporary closures of the road and continuous interventions on the roadway for its use, that caused significant inconvenience for the population and damage to the commercial, sanitary, touristic, agricultural and other activities. In 2018 a study has allowed to identify the kinematic characters of the landslide and the depth of the sliding surface. The study has confirmed that the principal causes of the landslide are the inherent characteristics of the clays which constitute the slope along with the high pore water pressures, and the fluctuations of these latter the causes of the continuous remobilisation. Very effective corrective measures have been identified in a system of drainage trenches, which represents a very simple and a not expensive solution for the stabilisation of the landslide.

Maurizio Ziccarelli, Antonio Casella, Giovanni Sapienza

Numerical Analysis of Stacked Geo-Tubes

Geo-tubes and geo-containers are being increasingly used as marine structures for coastal protection and harbor construction. They represent an alternative solution compared to the traditional methods such as rock embankment and/or concrete units, with a significant reduction in cost and time. The tensile stress of stacked geo-tubes in immersed condition has been explored in this paper through numerical modeling, considering that the main drawback for this kind of structures is the lack of definite design criteria. With the aim of increasing the knowledge of the shape of the tubes and of the tensile stress in the geotextiles after filling and loading, the analyses showed how these parameters may be influenced by many factors, as the mutual distance of the geo-tubes, the interface friction and the level of filling of the geo-tubes.

P. Pavanello, D. Tognolo, P. Carrubba, L. Frigo

Evaluation of Site Amplification for the Seismic Protection of a Strategic District in Naples

Since the 1980s, a Business District is located in the eastern area of Naples. The first pioneer studies carried out in this area showed that a significant variability of site amplification can be predicted due to the morphology of seismic bedrock and to the presence of vanishing lenses of peat. More recently, the seismic vulnerability of the New Law Court was assessed adopting the hypothesis of 1D conditions for the seismic response analysis. This paper aims at verifying the reliability of this assumption, evaluating the 2D seismic site response of a representative geological section. Geotechnical characterization of the soil deposits has been carried out by integrating the available experimental data with literature data. Two suites of accelerograms have been considered as input motions, representative of ‘near field’ and ‘far field’ seismic events. Equivalent linear and non-linear 2D analyses have been carried out through a finite element and a finite difference code, respectively. Results provide insights on the non-linear soil behaviour of peat and allow for recognizing the limits and advantages of both adopted approaches. Finally, the comparison between the results of 2D and 1D analyses allows for highlighting the effects of focalization of seismic waves on the amplification of the ground motion at the surface.

Juan M. Barbagelata, Giorgio A. Alleanza, Anna Chiaradonna, Anna d’Onofrio, Francesco Silvestri

Mechanised Tunnel Excavation Through an Instrumented Site in Rome: Class A Predictions and Monitoring Data

Contract T3 of Line C of Rome underground is currently under construction. The running tunnels, excavated using two EPB shields, cross the historical centre of the city, potentially interacting with the existing monuments of great historic value. For this reason, two fully instrumented control sections were established at the beginning of this contract, in representative ground conditions. In addition to a greenfield section, an embedded barrier of bored piles running parallel to the tunnel axis was monitored, to study its effectiveness for settlement mitigation. Class A predictions of the passage of the tunnels through the control sections were carried out using a recently developed advanced numerical procedure, modelling in detail the main physical processes occurring around the shield, including cutter-head overcut, shield tapering and tail void grouting. Hypoplastic laws, calibrated with all the available data from the geotechnical investigation, were employed to model the behaviour of the soil. In this paper, the numerical results are compared with preliminary data gathered during the passage of the TBMs, showing a good qualitative agreement and suggesting strategies to improve the predictions.

Nunzio Losacco, Giulia M. B. Viggiani

Assessing Future Variations in Landslide Occurrence Due to Climate Changes: Insights from an Italian Test Case

The paper compares the findings provided by empirical and physically-based models in estimating future evolutions in landslide occurrence as a consequence of the ongoing Climate Change. As test case, the phenomena affecting pyroclastic covers on Lattari Mts. (Campania Region) are considered. Simulation chains developed for both the approaches, pros and cons are carefully displayed pointing out the uncertainties currently associated to projections and the main gaps to bridge. Whatever the approach, an increase is expected but the relative magnitude and the evolution is deeply influenced by impact tools beyond the selected climate projections and concentration scenarios.

Guido Rianna, Alfredo Reder, Luca Pagano, Paola Mercogliano

Back-Analysis of the Post-Failure Stage of a Landslide Using the Material Point Method

In the present study, the material point method (MPM) is used to carry out a back-analysis of the post-failure stage of the Senise landslide that occurred in Southern Italy, in 1986. To this end, the final geometry of the landslide detected just after the event and the magnitude of the observed displacements of the landslide body are compared to those provided by the numerical simulations. The predicted configuration of the displaced soil mass matches the measured one very well when two slip surfaces, evidenced by the installed inclinometers, are accounted for in the analysis. In addition, the best agreement between observation and prediction is gained when the minimum values of the soil strength parameters determined experimentally are assumed. The present study proves that an appropriate analysis of the post-failure stage can lead to a better understanding of the complex mechanical processes of landslides, and help in establishing the most effective measures for land protection.

Antonello Troncone, Enrico Conte, Luigi Pugliese

Run-Out of Landslides Caused by Excess Pore Water Pressure Along the Slip Surface

Traditional numerical methods such as the finite element method and the finite difference method are generally adopted to analyze the slope response in the pre-failure and failure stages under the assumption of small deformations. On the contrary, the post-failure phase is often ignored because large deformations generally occur in this phase and the above-mentioned methods are unsuitable to deal with such problems. Indeed, a prediction of the landslide kinematics after failure is useful to minimize the risk of catastrophic damages or to establish the most suitable measures for land protection. In the present study, the post-failure stage of landslides caused by an excess of pore water pressure along the sliding surface is analyzed using the material point method (MPM), which is a numerical technique capable to overcome the limitations of the traditional methods. In particular, the influence of some involved parameters on the run-out distance of the displaced material is investigated.

Enrico Conte, Luigi Pugliese, Antonello Troncone

Prediction of the Mobility of Landslides Activated by Rainfall Using a Simplified Approach

This paper deals with the landslides activated by piezometric level changes owing to rainfall. Generally, the main type of movement experienced by these landslides is a translational slide with low displacement rate. In addition, deformations are essentially concentrated within a narrow shear zone above which the unstable soil mass moves as a rigid body. In view of this evidence, a simple approach based on a sliding block model was recently proposed by Conte et al. (2017) for a preliminary evaluation of the mobility of these landslides. This method relates landslide movements to rain recordings. This constitutes a significant advantage for land protection purposes because future displacements could be directly predicted from expected rainfall scenarios. In the present paper, a case study is analyzed to assess the predictive capability of the above-mentioned approach.

Enrico Conte, Antonello Troncone, Antonio Donato, Luigi Pugliese

Pore Water Regime in Active Earthflows and Effects on Slope Movements

The paper presents the results of long-term monitoring of pore water pressures and displacements in some active earthflows in highly fissured tectonized clay shales in the southern Italian Apennine. The number and variety of landslide sizes and the abundance of data allowed to draw a consistent picture of the earthflow behaviour. In particular, the experimental evidences point out the different influence of piezometric regime on the kinematic features depending on the landslide’s depth.

L. Comegna, J. De Rosa, C. Di Maio, L. Picarelli, M. Pirone, G. Urciuoli

Post-earthquake Resilience of a Room and Pillar Rock Cavity in Naples

The stability of ancient room and pillar cavities dug in seismic sites was modified by the occurrence of earthquakes during the time. In such complex systems, the seismic-induced modifications of resistances and loads may lead to local improvements of the condition under gravity loads. The paper proposes a probabilistic evaluation of such effect, in the frame of the performance based seismic assessment. The procedure was applied to evaluate the safety and the resilience of a room and pillar cavity dug in a rocky hill in Naples, known as Fontanelle cemetery, after the maximum credible earthquake. Non-linear dynamic analyses were performed on a refined 3D model calibrated on the available experimental data. The safety of pillars and rooms was evaluated against two limit states, defined as a function of the Ratio between the Capacity and the Demand, CDR. The CDR of room and pillars computed after the seismic analyses were compared to their values before earthquake to check the capability of the cavity components to face the earthquake-induced modifications of the static equilibrium and consequently evaluate their resilience.

F. de Silva, A. Scotto di Santolo

Feasibility of Foothill Barriers to Reduce the Propagation of Debris Avalanches

A numerical investigation is here presented about the beneficial effects of artificial barriers on the reduction of propagation of Debris Avalanches (DAs). Along natural open slopes DAs propagate as unconfined flows and usually travel hundreds of meters, with significant increase in volume during the propagation path. The idea of the research is that one or more barriers located at the foothill area can reduce the runout and constrain the flow movement in a designated area safely far from structures and people at risk. The “GeoFlow_SPH” model is used, as it allows the computation of the affected areas along with the height and velocity of the landslide mass. Different failure volumes and rheological properties are considered. The numerical results highlight how the position of the barriers may differently influence the flow features as well as the deposition zone. In the framework of the engineering implementation of such type of interventions, a preliminary discussion is presented about the optimal position and type of barriers.

S. Moretti, S. Cuomo, S. Aversa

The Contribution of Spaceborne SAR Data in Linear Infrastructures Monitoring Activities

The Italian territory is strongly affected by ground instability events such as landslides and subsidence phenomena, representing the main causes of damage along linear infrastructures network. For this reason, an effective monitoring system should be needed during the exercise phase to support control and management activities by owners and authorities. Actually, control of the Italian infrastructures is demanded to technicians and maintenance teams who detect, through visual control, anomalies and failures which require a site-specific monitoring. Such approach could represent a limited and only partial information to fully characterize and to investigate the infrastructure potential damage and can be highly expensive if a high density of measurements suitable for wide-scale infrastructure monitoring is required. Necessity of a very fast procedure for monitoring of these man-made infrastructures, finds in the application of modern remote sensing techniques a valid response to support infrastructures health assessments. In this work, Differential SAR Interferometry (DInSAR) has been used to investigate stability condition of S.P. 264 linear infrastructure, in Salerno Province (Italy), which is affected by several slow-moving landslides. Furthermore, an analysis of costs and benefits derived by using DInSAR technique has been provided. As result, the use such technology can be recommended for large areas studies, for which conventional punctual measurements can be highly expensive.

D. Infante, D. Di Martire, A. Scotto Di Santolo, D. Calcaterra, M. Ramondini

On the Reactivation of Sand Boils Near the Po River Major Embankments

Backward erosion piping is one of the most critical issues for the stability of the Po River embankments, which are reported to have experienced more than one hundred episodes of sand boils over the last century. This phenomenon is particularly widespread in the Po River for structural, hydrogeological and climatic reasons. This paper describes an in-depth study recently carried out on a large diameter sand boil located at the toe of a Po River major embankment in Guarda Ferrarese (Ferrara Province), which reactivated during a high-water event in autumn 2018. First of all, a 3D FEM model, devised to identify the hydraulic boundary conditions causing the sand boil to reactivate, is introduced. The numerical analysis, while proving to be effective in simulating past reactivations, showed that the proper modelling of the phenomenon relies on a number of parameters which are usually unknown. Accordingly, a novel field investigation was carried out during the November 2018 reactivation in order to collect a few relevant data (i.e. pipe geometry, hydraulic heads, water flow and velocities as a function of the river level) and thus reduce the uncertainties in the numerical model. This study aims at providing a new insight into the backward erosion piping mechanism and a contribution to the development of a reliable tool for the management of potentially dangerous reactivations of sand boils during increasingly recurrent high water events.

María Fernanda García Martínez, Guido Gottardi, Michela Marchi, Laura Tonni

An Early Warning System for Debris Flows and Snow Avalanches

To protect a mountain road against debris flows and snow avalanches that occur periodically along a gully, an innovative monitoring and early warning system (EWS) was designed, installed and tested. The system is based on a detection section equipped with 3 inclinometers suspended above the gully located at approximately 120 m upstream from the road, by two traffic lights, a weather station and two cameras. A wireless sensor network is used to manage the system so that all sensors and equipment can communicate through radio signal, without the need of cables. This solution was also chosen to reduce the overall environmental impact of the installation which took place in the Gran Paradiso National Park, in the North Western Italian Alps. In the case of an event, the detection section is triggered directly by the passage of the debris or the avalanche. An alarm data package is generated and transmitted to turn to red two traffic lights on the road thus stopping traffic. The paper will describe the monitoring and early warning system. Moreover, it will show how data collected by the weather station are used to manage in real time the attention and alarm thresholds allowing for limiting human intervention on the system and anticipating the increased probability of occurrence of events. Finally, a snow avalanche event occurred on the 8th January 2018 and detected by the early warning system will be illustrated.

F. Antolini, S. Aiassa, M. Barla

Liquefaction Hazard Evaluation for a 3rd Level Microzonation Study in a High Seismicity Area of Central Italy

Widespread liquefaction phenomena may also occur in surface alluvial intermediate soils composed of alternations of saturated sandy silts, silts, silty and clayey sands, during earthquakes of moderate magnitude as experienced for the 2012 Emilia Romagna seismic sequence. By the consequence, liquefaction hazard evaluation has been included in the most recent 3rd level microzonation studies promoted by some Regional Governments. The paper presents the results of one of those studies performed for the municipality of Barberino di Mugello that falls within a high seismicity area of Central Italy including typical Appennine intramontane basins where surface alluvial soil layers that overlay fluvio-lacustrine soil deposits can be frequently encountered. With reference to the studied area, the liquefaction potential and the expected settlements of intermediate soil deposits are calculated by using different simplified methods and the corresponding liquefaction hazard maps are presented and discussed.

J. Facciorusso, C. Madiai, G. Vannucchi, E. Gargini, M. Baglione

An Integrated Model for the Assessment of Subsidence Risk in the Area of Bologna (Italy)

The rapid and uncontrolled evolution of urban and industrial settlements often turns to be unsustainable for the natural and anthropic system. A prominent example is the subsidence induced by intensive groundwater exploitation. Assessing the risk produced on urban agglomerations by the groundwater table drawdown enables to visualize the impact and to undertake policies that protects structures, infrastructures and, more generally, the socio-historical-cultural environment of the cities. This task implies to assemble hydrological, hydrogeological and geotechnical factors into comprehensive models that lead to compute free field deformation. Interfacing this effect with the mechanical characteristics of buildings or infrastructures allows to quantify damage severity. The present paper reports a study carried out for the city of Bologna, one of the most emblematic examples in Italy, whose old town and suburbs have undergone an extensive and continuous subsidence from the early seventies. An integrated risk assessment methodology is implemented defining the paramount factors, intensity measures, engineering demand parameters, vulnerability and exposure and building an interpretative model based on observation.

Rose Line Spacagna, Giuseppe Modoni, Michele Saroli

On the Stability of a Fully Instrumented River Embankment Under Transient Conditions

Time-dependent boundary conditions, uncertainties and variability of soil suction and water content of the filling material together with the use of proper retention and strength soil models are crucial aspects to be included for reliable analyses of the actual stability of river embankments. However, due to a typical lack of information in many practical cases, the use of simplistic assumptions on both hydraulic and mechanical response of earth infrastructures to hydrometric water level fluctuation and atmospheric loading is largely diffused, thus providing erroneous conclusions on the effective safety margins towards possible slope instability and collapse. Within this context, site measurements down to relevant depths, combined to an accurate soil characterization under partially saturated conditions, can be extremely useful to evaluate unsaturated variables (i.e. soil water content and suction) under transient flow conditions and hence carry out realistic stability analyses. A comprehensive monitoring system has been therefore designed and installed on a relevant representative section along river Secchia, a right-hand tributary of river Po (Northern Italy). The paper aims at presenting a methodological approach for a sustainable performance assessment of such geotechnical infrastructures, based on the complementary use of laboratory tests, field measurements and numerical analyses.

C. G. Gragnano, I. Bertolini, I. Rocchi, G. Gottardi

Deterministic and Probabilistic Analyses of Slopes Reinforced with Vegetation

Root reinforcement can be used conveniently for risk mitigation against shallow landslides as well as for slope erosion control. For taking into account the plants contribution, the Mohr-Coulomb failure criterion can be modified using an additional term representing both the contributions of the tensile strength of roots and their spatial distribution inside the soil. This paper shows the results of several slope stability deterministic analyses under seismic conditions, carried out to study whether or not the vegetation effect is positive on slope stabilization. These analyses have been performed for different slope geometries using the pseudo-static approach applied to the simplified Bishop’s Method. Thereafter, the same slope geometries have been analysed by using the probabilistic approach in order to quantify the reliability level of these sustainable measures, since both soil and plants are characterised by high inherent uncertainty and variability.

M. Pisano, G. Cardile, A. Ricciardi

Mechanical and Physical Effects of Electroosmotic Dewatering of Clayey Soils

Electrokinetic (EK) treatment is studied for fine grained dredged soils as an innovative and cost-effective method to accelerate the dewatering and improve their mechanical behaviour. Owing to their high-water content, the dredged sediments take a very long time for the consolidation process, much more than those considered in the typical problems of geotechnical engineering.Some electroosmotic tests in oedometer conditions on a clayey soil have been carried out at the University of Napoli Federico II in a special apparatus (special oedometer), adopting a pore fluid with different salt concentration. The results show that the addition of soluble salts in small quantities (until 8 g/l) can improve the electroosmotic consolidation of soft clay. On the contrary, excessive salinity reduces the efficiency of electroosmotic dewatering. The optimal salinity content has been then determined. At the end of the EK tests, some triaxial tests have been performed on the treated specimens in order to analyse the effectiveness of the EK treatment in the improvement of the soil mechanical properties.

S. Gargano, S. Lirer, A. Flora

The Use of Seismic Records for Updating the Geotechnical Model for a Site in San Giuliano di Puglia (Italy)

The aim of this paper is to develop an update of the existing subsoil model for the site in San Giuliano di Puglia (Italy), where the primary school F. Jovine collapsed after the 2002 Molise earthquake. To this end, we performed a site response back-analysis using the data from seismic stations recently installed in the village to obtain a proper input motion and to validate the results of the computations. To implement a 1-D subsoil model, we scrutinized the geotechnical tests recently performed in the area as well as previous studies conducted on the same site. Then, we performed a parametric 1-D site response analyses varying shear wave velocity profiles and the depth of the bedrock. The most appropriate subsoil model, characterized by higher soil stiffness, results substantially different from the one proposed in previously published studies of the seismic response of the city.

Tony Fierro, Luciano Mignelli, Giuseppe Scasserra, Alessandro Pagliaroli, Filippo Santucci de Magistris

The “Strange” Case of the Scorciavacche Failure

Just after the completion of the upgrading works of the SS 121 national road connecting Palermo to Agrigento, in Sicily, the brand-new embankment linked to the northern abutment of the Scorciavacche viaduct suffered of two instabilities along the downhill side slope, causing the loss of two separate road segments of around 250 metres of total length. Early bird interpretation of the collapses ascribes the failures to a bearing capacity problem, consequence of the inadequacy of the embankment foundation. Surprisingly for the many actors on the scene, the subsequent forensic investigations have shown that the causes of the failure were different and not at all easily readable from the non-exhaustive observations of the initial scrutiny. Thorough geological and geotechnical investigations together with the monitoring of the site over a wide area made instead possible to discover clear signs of a quiescent instability which was bounded by a pre-existing failure surface that undoubtedly played a role in fixing the geometrical features of the collapses. The different picture of the scene that emerged after a careful geomorphological survey, a sound geotechnical investigation and a sufficiently long monitoring, convinced the technical experts of the defence that a wider scale model was needed to interpret this failure case that could not so simply be reconducted to a classical bearing capacity problem.

G. Scarpelli, G. Scozzari, A. Vita, D. Segato

A Macroelement Approach for the Stability Assessment of Trees

Interaction diagrams in the generalized 3D loading space of vertical (V), horizontal (H) and moment (M) actions constitute the basis of the design of foundation structures in case of complex loads combinations. The mechanical response of such systems is frequently interpreted in terms of the ‘macroelement’ theory, where a generalized incremental constitutive relationship is introduced, linking the displacements and rotations of the foundation (playing the role of generalized strains) to the histories of applied loading components (i.e. the generalized stresses). In this paper an attempt to extend a classical macroelement framework, to the case of root-soil interaction presented. The model is calibrated on small scale experimental data on 3D printed plastic root systems, subject to combined V-H-M loads, and a parametric analysis on the main governing parameters is discussed. The comparison between numerical and experimental data suggests that the macroelement approach could be an efficient and simple analytical tool for describing the whole moment-rotation curve, overcoming the main simplifying hypotheses currently employed in arboriculture practice.

G. Dattola, M. O. Ciantia, A. Galli, L. Blyth, X. Zhang, J. A. Knappet, R. Castellanza, C. Sala, A. K. Leung

Development

Frontmatter

Punching Tests on Deformable Facing Structures: Numerical Analyses and Mechanical Interpretation

Anchored wire meshes, commonly adopted to stabilise potentially unstable slopes in granular soils, are composed of wire meshes, geosynthetics, anchorage bars/ties and spike steel plates. In many cases, this reinforcement system is employed as a “passive” reinforcement, i.e. it transfers loads to the unstable domain only when this develops irreversible displacements. During this displacement accumulation, complex interaction mechanisms between the deformable reinforcement system and the underlying material take place. To study these interaction mechanisms, a series of large displacement 3D FEM numerical analyses is performed. The mechanical behaviour of the material constituting the wire mesh and the soil is reproduced by means of elastic-perfectly plastic constitutive relationships. In particular, for the mesh a von Mises failure condition and an associated flow rule are employed, whereas for the soil a Mohr-Coulomb criterion and a non-associated flow rule. The constitutive parameters are calibrated on a series of experimental punching test results. The numerical results are reported by means of the characteristic curve, relating the penetration of the steel plate to the system reaction force. In order to stress the role of (i) both soil and wire mechanical behaviour and (ii) the spike plate dimensions in influencing the mechanical response of the whole system, the results of a parametric study are finally discussed.

Katia Boschi, Claudio di Prisco, Luca Flessati, Andrea Galli, Marianna Tomasin

A Predictive Model for Pullout Bearing Resistance of Geogrids Embedded in a Granular Soil

Currently, Geosynthetic-Reinforced Soil (GRS) structures represent one of the most sustainable solutions capable to improve the protection of the territory, guaranteeing high performance (especially in seismic field) with construction costs that are lower than those required for the more traditional Civil and Environmental engineering works. To design such types of structures the knowledge of soil-geosynthetic interface parameters is necessary, and their prediction is very complex due to the elementary interaction mechanisms affecting the pullout resistance of geogrids embedded in soils that are mainly the skin friction between soil and the reinforcement’s solid surface, and the bearing resistance developing on transverse elements. When the spacing between the geogrid’s transverse elements is below a threshold value, the interference mechanism develops and it can affect the bearing resistance, as the passive surfaces cannot be entirely mobilised on bearing members. In order to model the peak pullout resistance of extruded geogrids embedded in a compacted granular soil, the paper deals with a new experimental validation of a theoretical method taking into account the interference mechanism.

G. Cardile, M. Pisano, N. Moraci

The Effect of Densification on Pieve di Cento Sands in Cyclic Simple Shear Tests

The main aim of this work is to study the effectiveness of densification as a mitigation technique against liquefaction, by means of cyclic simple shear tests carried out on specimens reconstituted at several relative densities. The adopted cyclic simple shear apparatus works with a sophisticated control system, which allows to carry out tests in k0 condition without using confining rings. Two different Italian sands were tested, both retrieved at Pieve di Cento (Emilia Romagna Region, affected by 2012 earthquake) at different depths. The results of cyclic simple shear tests show that densification increases the resistance to liquefaction. The expression of Booker et al. (1976) has been also used to simulate the trend of excess pore pressure ratio with the ratio between number of cycles and number of cycles at liquefaction of the experimental undrained cyclic tests.

L. Mele, S. Lirer, A. Flora

Evolution of Local Strains Under Uniaxial Compression in an Anisotropic Gypsum Sample

In the fields of geomechanical researches and applications, the study of mechanical properties of rock materials through laboratory tests is a fundamental milestone in the process of understanding and modeling the mechanical behavior and the stability assessment. In particular, the study and quantification, in laboratory samples, of the local strains and of their concentration and localization during the application of an external load may allow for a more accurate description of the material behavior.In this study, we focused on a specific gypsum rock with a strongly anisotropic structure. The strategic importance of gypsum in the construction industry and its consequent extensive exploitation by both open pit and underground quarries requires a good knowledge of its strength and stress-strain relation. We propose an application of Digital Image Correlation (DIC analysis) to the study of the evolution of local strains in gypsum rock under the application of a uniaxial compression. Resulting maps of local strains were analyzed and interpreted considering the influence of textural variability of the material. In consideration of the material anisotropy, DIC analysis was applied on two adjacent faces of a prismatic sample, allowing for a three-dimensional interpretation of strain evolution.

Chiara Caselle, Gessica Umili, Sabrina Bonetto, Daniele Costanzo, Anna Maria Ferrero

On the Effect of Grading and Degree of Saturation on Rockfill Volumetric Deformation

The use of rockfill in civil engineering works such as earth and rockfill dams, road and railway embankments, increased along the last century especially for sustainability reasons. In order to ensure the stability of these structures under a set of conditions expected to occur during their life (grain crushing, changes in degree of saturation), the prediction of mechanical behavior of rockfill is fundamental for land management and protection. The mechanical behavior of rockfill mainly depends on stress level and relative density, as usual for granular soils. However, because of the large size of the particles, their mineralogical characteristics play a relevant role too, influencing grain crushing and therefore the overall behavior. Furthermore, it has been demonstrated in literature that for a given state (defined as the combination of stress state, void ratio and average number of grain to grain contacts) the effect of grains mineralogy on grain crushing (or microcrushing) largely depends on relative humidity (RH). The paper presents the results of triaxial tests performed on gravel specimens in which different levels of relative humidity are explored in order to analyze the “driest” and “fully saturated” conditions, and the transition from one to the other. Grain size distributions of the specimens, both after compaction and after the triaxial tests, are also compared in the paper.

Roberta Ventini, Alessandro Flora, Stefania Lirer, Claudio Mancuso

DEM Simulation of Frozen Granular Soils with High Ice Content

High volumetric ice content is one of the structural features of alpine permafrost. The mechanical properties of pure ice are very different from those of dry soil and as a consequence the mechanical properties of frozen soil are highly dependent on the ice content, as highlighted by triaxial experiments available in the literature. On the basis of existing data from experiments under different stress paths (axis-symmetric compression and extension), this paper presents a frozen soil model by using the particle-based discrete element method (DEM). In the model two groups of elements are used for representing soil particles and ice, and two separate sets of micromechanical parameters are calibrated and assigned to each group. Elements from the two groups are then mixed in different proportions in order to simulate the effect of ice content. A series of triaxial compression simulations are then performed and analysed.

Guodong Wang, Francesco Calvetti

The Effects of Structure on the One Dimensional Compression Behaviour of a Porous Calcarenite

Human settlements built on weak rock deposits are often characterized by instabilities or collapse that may involve the underground cavities and consequently the above buildings. Underground calcarenite quarries in Marsala have been involved in a number of collapses that have seriously damaged numerous buildings. Unfortunately proper engineering solutions have not yet been identified according to the different and special cases and to the properties of this structured material. In order to investigate structure effects on the behaviour of the porous calcarenite of Marsala, this paper presents a comparison between the one dimensional compression behaviour of the intact rock and of the same weak rock in the reconstituted state. The investigated lithotype is a metastable rock whose mechanical behaviour is strongly affected by its structure, which is commonly distinguished in the literature as a combination of fabric and bonding. The investigation has highlighted original results, not reported in the literature for this material, such as the irrelevance of bonding in determining the stiffness. A laboratory study was also undertaken to assess the use of polymer treatment or inorganic consolidants as a solution to improve the mechanical behaviour of this weak rock.

M. Zimbardo, A. Nocilla, M. R. Coop, L. Ercoli, B. Megna, M. C. Mistretta

Artificial Intelligence to Predict Maximum Surface Settlements Induced by Mechanized Tunnelling

Among the construction methods developed for tunneling, mechanized excavation by Tunnel Boring Machines (TBMs) is currently considered a preferred option for technical and safety reasons in an urban environment, where damage induced on pre-existing building and services should be minimized. Since the ability to predict TBM performances is a critical point required to enhance the quality of the excavation and to optimize time, cost and safety operations in a project and since real-time prediction should be done during excavation in order to adjust some parameters in very real-time, approaches based on Artificial Intelligence (AI) methodology could be crucial. This study proposes an expeditious tool based on the application of Artificial Intelligence and particularly Artificial Neural Networks (ANNs), to predict the maximum surface settlements induced by tunnelling. ANNs, taking advantage of the quality of data available and computational performances of software for data management, have been proved to be a reliable instrument in processes where a relevant number of parameters and acquired measurements have to be managed. Using data selected from the excavation of the Milan M5 metro line, the document includes details on the role played by several inner elements on the accuracy of the final prediction based on the comparison of several different ANN configurations. The obtained results showed a promising capability of the tool to swiftly predict surface settlements in mechanized tunneling projects.

Mohsen Ramezanshirazi, Diego Sebastiani, Salvatore Miliziano

Enhancement of Design Methodologies of Anchored Mesh Systems Using the Discrete Element Method

The understanding of the mechanical behavior of anchored mesh systems for slope stabilization represents a challenging task for engineers. Standard laboratory tests are in general not representative of the in-situ conditions. Moreover, the complex interaction between the mesh and the retained material is not trivial to reproduce numerically. In this study a simplified in-situ condition is analyzed using the discrete element method (DEM). Starting from the tensile stress-strain relationships acting on each wire it is possible to determine the force sustained by the mesh system and to derive the displacement field of the mesh panel. Therefore, the progressive activation of the mesh retaining capacity, during the loading of these structures can be obtained providing the evolution of the mechanical response of the system. The information obtained with the discrete element simulation highlights the possible improvements of the classical design methodologies and shows the potential of the presented approach for the comprehension of the mechanical behavior of anchored mesh systems.

A. Pol, F. Gabrieli, N. Mazzon

Seismic Soil-Pile-Structure Interaction. Theoretical Results and Observations on Pile Group Effects

In this paper the fundamental features of the seismic soil-structure interaction on the response of pile-supported structures are investigated. A stiffness matrix approach is proposed and employed to analyze the dynamic behavior of single pile and pile groups embedded in homogeneous and heterogeneous soil deposit. The superposition theorem is then used to evaluate the response of the structure, modelled as a single degree of freedom oscillator. Different configurations of both piles and structures are considered. In particular, the aim of the present study is to explore the role of the dynamic properties of the soil and pile group effects on the dynamic response of the structure. The performed analyses permit to define reliable seismic design criteria of piled-structures.

Roberto Cairo, Giampaolo Francese, Rossana Moraca, Federica Aloe

Rock-Engineering Design and NTC2018: Some Open Questions

The Italian technical standard of construction (NTC-2018) defines the standards for designing, building and testing all kinds of constructions, considering their performances in terms of mechanical resistance, stability and durability. These standards give us the general safety criteria, stating that the effect of actions and material characteristics must be included in the design. Moreover, NTC-2018 transposes requirements suggested in the EN Eurocodes (EN 1990 - EN 1999). For what it concerns geotechnical structures, since 2010, EN-1997 Geotechnical Design (EC7) has been the reference design code for construction in the EU. What about rock engineering designs? Since rock mechanics is a branch of geotechnics, rock-engineering constructions should be designed following EC7 and NTC-2018 requirements. However, their applicability is not obvious, since the use of partial factors in design calculation is not allowed due to lack of proper partial factors or since there are no precise indications about the processing of data coming from new analysis techniques (e.g. remotely sensed data). For rock masses, partial factors may be applied to joint strength but they cannot be used for joint orientation or spacing. As a consequence, statistical approaches, together to detailed geomechanical surveys (traditional and/or non-contact) are more suitable for these parameters. In this paper, the authors analysed some open questions in national and European regulations related to rock-engineering design.

F. Vagnon, S. M. R. Bonetto, A. M. Ferrero, M. R. Migliazza, G. Umili

Geotechnical Hazards Caused by Freezing-Thawing Processes Induced by Borehole Heat Exchangers

In closed-loop Ground Source Heat Pump system (GSHP), the thermal exchange with the underground is provided by a heat-carrier fluid circulating into the probes. In order to improve the heat extraction rate during winter, the heat-carrier fluid temperature is often lowered down to −5 °C; this way, the induced thermal anomaly is more intense and can cause freezing processes in the surrounding ground. In sediments with significant clay fraction, the inner structure and the porosity distribution are irreversibly altered by freezing-thawing cycles; therefore, the geotechnical properties (such as deformability, stiffness and permeability) are significantly affected. A wide laboratory program has been performed in order to measure the induced deformations and the permeability variations under different conditions of thermal and mechanical loads and interstitial water salinity. The results suggest that, despite the induced frozen condition is quite confined close to the borehole, the compaction induced in cohesive layers is significant and irreversible and could generate negative friction on the borehole heat exchanger; in addition, the permeability increase in the probe surroundings could lead interconnection among aquifers, with increasing effects with the number of boreholes in the borefield.

S. Cola, G. Dalla Santa, A. Galgaro

Site Specific Seismic Performance of Circular Tunnels in Dry Sand

Past earthquakes revealed that underground tunnel structures are exposed to seismic risk and their seismic vulnerability is mainly function of the tunnel structure technology, the soil-tunnel interaction developing during the seismic shaking and the intensity of the seismic event. Each of these factors plays an important role in terms of the probability of damage and loss of functionality due to the tunnel deformations induced by increments in internal forces. Currently, the fragility curves are among the most widespread methods for the rapid assessment of structural performance at different hazard levels, giving the probability of reaching a defined damage level with respect to a given level of seismic motion. In the present work, a recently developed approach to evaluate the seismic risk has been applied to circular tunnels, whereby the main focus is the expression of the failure annual rate through the convolution of the fragility of the system under investigation and the seismic hazard on site. In this way, a direct link between the performance of the structure with its measuring parameter is established. The procedure has been adopted for some reference tunnel sections of the Metro Line of Naples.

F. de Silva, S. Fabozzi, N. Nikitas, E. Bilotta, R. Fuentes

Experimental Study on a Three-Dimensional Passive Earth Pressure Coefficient in Cohesionless Soil

Estimation of the passive earth pressure is a crucial aspect in several geotechnical design problems. Several authors presented two-dimensional models for its evaluation while three-dimensional (3D) approaches have received less attention. It has been recognized that in many geotechnical systems, such as anchor blocks or plates or everywhere the width of the load area is limited if compared to its height, the three-dimensional passive earth pressure is quite different from the two-dimensional one and, due to side effects, is generally larger. This paper is concerned with an experimental and numerical study of 3D passive earth pressure encountered by a rigid plate of limited width in a cohesionless soil. The obtained results allowed the evaluation of a three-dimensional passive earth pressure coefficient which is not only dependent on the soil friction angle, as it occurs in a 2D formulation, but also on the ratio of the width to the height of the load area.

P. Capilleri, E. Motta, M. Todaro, G. Biondi

Optimization of the Geometry of Monitoring Devices for Contaminant Detection in Cement-Bentonite Cutoff Walls

Cutoff walls represent an interesting solution for the containment of the pollution of superficial groundwater. For polluted sites, the purpose of a cement-bentonite cutoff wall is to minimize contaminant transport and the primary design requirement for such materials is the low hydraulic conductivity. Despite these barriers are often cast in place as provisional tools, recently their wide use imparted the need for a better understanding of cement-bentonite walls also in the long-term. This certainly implies not only the need to study the time evolution of the cement-bentonite hydro-mechanical properties in a contaminated environment, but also the necessity of a continuous monitoring of the efficiency of the system. To this aim, the use of dedicated devices cast in place inside the wall when the mixture is still fluid proved to be particularly suitable to intercept and analyse the fluids flowing through the barrier. In this paper, the results of a numerical study are presented, with the goal of suggesting criteria about the optimum spacing and geometry of these devices.

Giulia Scelsi, Gabriele Della Vecchia, Claudio di Prisco, Guido Musso, Gianluigi Sanetti

A Coupled Study of Soil-Abutment-Superstructure Interaction

This paper presents a coupled numerical modelling of the soil-structure interaction for a multi-span girder bridge, inspired by a case study in Italy, to analyse the importance of the local dynamic response of the abutments in the seismic performance of the bridge. The full soil-bridge model was implemented in the analysis framework OpenSees, describing the mechanical behaviour of the foundation soils by means of an advanced constitutive model calibrated against experimental data. The results of the simulations demonstrate the relevance of the inertial effects, deriving from the dynamic response of the embankment, that enhance the non-linearity in the behaviour of the soil-abutment system. The present study is part of a wider research project concerning the dynamic behaviour of bridge abutments and its effects on the global structural performance. In this view, the proposed soil-bridge representation constitutes a benchmark for the validation of simpler analysis methods, using macro-element representations for the simulation of the dynamic response of the soil-abutment system.

Davide Noè Gorini, Luigi Callisto

Performance of a Deep Excavation for the New Line C of Rome Underground

The construction environment of tunnels and deep excavations is often very complex because of the presence of pre-existing buildings, often of historical or architectural value. Therefore, the accurate control of excavation stages and the use of intense monitoring for early warning of potential damage is essential to ensure that nearby structures would not be affected by ground deformation. This is particularly relevant for the city of Rome, where a new metro line is being constructed in the historical city centre, facing significant problems for the presence of archaeological artefacts and for the necessity of minimising the effects on the historical and monumental heritage. This paper describes the field performance of a 30 m deep excavation which has been constructed at short distance from the ancient masonry walls of the city, the Aurelian Walls of Roman age. An extensive instrumentation program was conducted during construction. Field observations included deflections of diaphragm walls, ground displacements, pore water pressures and settlements of surrounding buildings and those of the city walls. Analyses of field data indicated that ground settlements and diaphragm wall deflections were smaller than those observed in other case histories worldwide, with only negligible effects observed in the Aurelian Walls.

Luca Masini, Sebastiano Rampello, Eliano Romani

Preliminary Numerical Simulation of Centrifuge Tests on Tunnel-Building Interaction in Liquefiable Soil

This paper shows the results of preliminary numerical analyses performed to simulate centrifuge tests that will be carried out for the project STILUS within the framework of the European funded network SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe). The aim of the project is to investigate the problem of tunnel-structure interaction in liquefiable soil through a series of centrifuge tests and to assess an effective mitigation technique. Two models will be tested in centrifuge, in the first one only the tunnel is modelled while in the second one a simplified structure on strip foundations is added. In order to analyze a cut-and-cover tunnel in an urban environment a rectangular section has been assumed. The tests were simulated by means of Plaxis 2D and the soil was characterized by PM4Sand model. The results were evaluated in terms of pore pressure build up, accelerations and settlements. The distribution of excess pore pressure induced around the tunnel and the building basement may also be useful to identify where mitigation techniques that may locally reduce pore-pressure build-up would be most effective against the effects of soil liquefaction and should be implemented in the forthcoming tests.

G. Miranda, V. Nappa, E. Bilotta

Exploring Static Instability Behavior of Sand-Fines Mixtures Based on Different State Variables

The paper presents a study aimed at evaluating the effect of non-plastic fines on undrained static liquefaction and instability behavior of silty sands considering two different state variables: (global) void ratio (eo) and equivalent granular void ratio (e*). The last parameter was introduced as an alternative index for mixed soils with a “sand-dominated” fabric. Undrained monotonic triaxial tests were carried out on Ticino sand-silt mixtures (FC = 0–30%) for a wide range of initial void ratios and mean effective confining stresses. The study provides evidence that, when the (global) void ratio is used as the comparison basis, the effect of fines is to cause an increase in the degree of contractiveness and higher susceptibility to collapse. Nevertheless, when the comparison is made at constant equivalent granular void ratio, undrained shear behavior and collapsibility of the silty sands are closely related to e*, which appears an effective index for unifying the response of mixed soils with varying fines content.

Daniela D. Porcino, Giuseppe Tomasello

Site Response Analyses for Post-Earthquake Reconstruction in the Area of L’Aquila: Influence of the Input Subsoil Model

Significant local amplifications of the ground motion and variable damage distribution are characteristic features, among other observed effects, produced by the 2009 L’Aquila (Italy) earthquake. Site response analyses may play an important role in post-earthquake reconstruction, aiming at protection of the territory and mitigation of the effects of future earthquakes. The paper describes the results of site response analyses in the urban area of L’Aquila, focusing in particular on the influence of assumptions made in the definition of the input subsoil model. This issue is discussed with the aid of an example for one representative site (Pettino – San Sisto area).

Paola Monaco

The Analysis of Weak Rock Block Behaviour by an Advanced Constitutive Model

In this paper the behaviour of rock cliffs is numerically analysed, aiming at exploring the possible triggering and propagation of instability of rock blocks related to environmental agents and anthropic activities. At this scope a hierarchical elastoplastic constitutive model for structured soils and weak rocks is adopted.

A. Amorosi, F. Rollo, L. Gagliardini

Application of a Statistical Approach for the Assessment of Design Block in Rockfall: A Case Study in Sesia Valley (Northern Italy)

Rockfall is one of the most dangerous and unpredictable slope instabilities. Modelling this phenomenon is a very complex issue because of the high number of variables influencing the triggering and the propagation phases. In particular, the choice of the design block volume can affect the results of the propagation analysis as well as the reliability of the risk mitigation structures (Hungr et al. 1999). Thus, De Biagi et al. (2017b) proposed a methodology based on a statistical approach for building a fallen blocks volume-frequency law. The approach takes into account both the volumes of fallen blocks measured onto the slope and the historical events, providing a relationship between the volume and the recurrence period. A subsequent note (De Biagi 2017) suggests how to take into account the errors that can be made with this methodology due to the usual limited number of recorded events and surveyed blocks. In this paper, the statistical method is applied to a case of recurrent rockfall events that affect Nosuggio village, located in the Sesia Valley (North Piedmont, Italy). The study shows how it is possible to obtain a reliable volume-frequency law even in the case in which a well-structured survey of the blocks is not easy to perform.

M. Barbero, M. Castelli, G. Cavagnino, V. De Biagi, C. Scavia, G. Vallero

Field Tests on Screw Micropiles Under Axial Loading

Screw micropiles consist of a steel tubular shaft with continuous spiral threads, and a threaded tapered segment at the bottom. They have some notable advantages over conventional micropiles: grouting is not required; they are quick to install and immediately loadable, easy to dismantle and reusable; no earthwork is required prior to installation and damage to the soil is minimal after removal; because the installation equipment is small, they are suitable where the access is limited. Although these piles are potentially useful in many applications as well as being environment-friendly, research on their behavior is limited. The paper presents an ongoing experimental study on the axial response of screw piles. A test site in Cornovecchio (Lodi, Italy) was selected and characterized by means of in situ and laboratory tests. A number of field tests of full—scale micropiles, with diameter varying from 66 to 114 mm and length varying from 0.8 to 1.6 m, were undertaken to investigate the piles’ capacity under axial tensile and compressive loads in predominantly cohesive soils.

Alex Sanzeni, Emanuele G. Danesi, Pier Luigi Subitoni

A Simplified Approach for the Estimation of Settlements of Earth Embankments on Piled Foundations

In recent years, the employment of deep foundations as settlement reducers has become increasingly popular in the design of earth embankments over soft soil strata. To further improve the system response, geosynthetic layers are often positioned at the embankment base. Owing to the presence of both piles and geosynthetics, complex interaction mechanisms, transferring stresses towards the piles and reducing those on the soft foundation soil, take place. Although these mechanisms are governed by the relative stiffness of the various elements constituting this system (piles, foundation soil, embankment and georeinforcements), the approaches commonly adopted to design these “geostructures” do not explicitly take into consideration the stiffness of the single element as design parameters. Moreover, the effect of the stepwise embankment construction process is often disregarded. As a consequence, the settlements at the top of the embankment cannot quantitatively be estimated.In this paper a new model for the evaluation of the settlements at the top of the embankment, considering both the deformability and the yielding of the soils, is presented. The model introduces both the geometry and the soil mechanical properties as constitutive parameters, and explicitly puts in relationship the embankment settlements to the embankment height (herein considered as a generalized loading variable), thus allowing the geotechnician to adopt a direct displacement-based design approach.

Claudio di Prisco, Luca Flessati, Andrea Galli, Viviana Mangraviti

Geogrids as a Remedial Measure for Seismic-Liquefaction Induced Uplift of Onshore Buried Gas Pipelines

The use of geogrids in geotechnical engineering is increasing over the years and it has been mostly studied in the applications of steep slopes, retaining structures and embankments constructed over soft foundations. The increase in liquefaction resistance for sandy soils by using fiber reinforcements started to be considered but the use of geogrids to mitigate liquefaction phenomenon needs to be further investigated. Here, the application of geogrids sheets to prevent the seismic-liquefaction induced uplift of a buried onshore gas pipeline in saturated sandy soil is described by the results of 1-g shaking table tests performed at the geotechnical laboratory of the University of Tokyo in a model scale of 1:10. A Silica Sand with a relative density of ~50% is used, a 40 cm long DN100 PVC pipe with an apparent unit weight of 0.68 g/cm3 is buried in the soil model and 3 geogrid sheets of dimensions 30 cm by 40 cm with an interlayers distance of 3.5 cm are placed above the pipe as remedial measure. Applying sinusoidal shaking with different amplitude, the model response is studied. Geogrids resulted an effective tool to mitigate pipe displacement in case of liquefaction.

Massimina Castiglia, Filippo Santucci de Magistris, Salvatore Morgante, Junichi Koseki

FEM 3D Analysis of Settlements Induced by Shallow Tunnels in Coarse-Grained Soils

The paper is focused on some aspects of 3D numerical modelling of shield-driven tunnels in coarse-grained soils. Different approaches for modelling soil-shield interaction are considered and their impact on the predicted settlement trough is analyzed. These approaches have been applied for modelling two well documented case histories of one tunnel bored in green field conditions. The tunneling process has been simulated step-by-step in order to represent relevant features, such as, application of face pressure, installation of a segmental lining, grout injection and time-dependent variation of grout stiffness. The soil mechanical behavior has been modelled by the Hardening soil model with small strain stiffness implemented in the Plaxis 3D software. Soil deformation around the shield has been modelled by three different approaches: Shield contraction, E-modulus reduction and Strain applied method. Settlement distributions obtained by E-modulus reduction and imposed strain methods are generally in better agreement with field monitoring data but require a specific calibration. Numerical results concerning the structural forces in the lining and the stress paths of representative soil elements are also discussed.

F. Schiena, A. Lembo Fazio, A. Graziani

A New Methodology for the Rock-Burst Assessment During Tunnel Construction

Risk associated to rock-burst occurrence in tunnels is nowadays managed by a continuous monitoring of acoustic emissions recorded during the excavation, whose characteristics depend on the failure processes ongoing in the rock-mass. A new in situ test was specifically designed with the aim of calibrating the alarm threshold for rock-burst occurrence. The test consists in compressing to failure a portion of the rock-mass at the tunnel side-wall by means of a couple of flat-jacks, measuring simultaneously the generated acoustic emissions with accelerometers. The test was for the first time carried out at the Brenner Base Tunnel in massive granite below an overburden of about 1200 m, nearby tunnel locations affected in the past by few mild rock-burst phenomena. Recorded data clearly indicated that a correlation exists between the energy and frequency content of the acoustic emissions and the rock-mass failure. Following the experimental investigation, and consistently with the available monitoring evidence, a new higher alarm threshold was implemented at the construction site. Further tests are currently in progress: these are aimed to validate the results and to produce a testing standard that may be applied to the construction of tunnels affected by rock-burst phenomena.

A. Voza, L. Valguarnera, S. Fuoco, G. Ascari, D. Boldini, D. Buttafoco

Effects of Thickeners Polymers Used in Tunnelling on the Physical and Mechanical Properties of Fine-Grained Soils

The most effective, safe and controlled way to perform tunnel excavations is through the use of Tunnel Boring Machines. This technology often requires the injection of chemicals to modify the soil properties, enhancing the control on the pressure applied at the front-face and consequently reducing the risks related to unexpected surface settlements, to excessive abrasion of the excavation tools and to clogging phenomena inside the working chamber. Since the reuse of the excavated soil is rapidly gaining importance, studies focused on the effect of these chemicals on soil properties, from both the geotechnical and environmental points of view, begin to be carried out more frequently in support of the design. This study addresses the evaluation of the effects of chemicals on the physical and mechanical properties of fine-grained soils: laboratory measurements of the effects on soil plasticity and on the associated variations in compressibility and undrained and residual strength of several samples of fine-grained soils from real tunnelling projects are presented. The results provide interesting insights on the interaction between the soil and the injected chemical, useful to better understand the most suitable use and dosage of the chemical and to consider its effects when reusing the conditioned soil.

D. Sebastiani, A. de Lillis, A. Di Giulio, S. Miliziano

Time Evolution of the Height of Dredged Mud in a Containment Facility: A Comparison Between Monitoring Data and Numerical Predictions

An efficient and sustainable way to handle dredged sediments is to re-use them to fill coastal containment facilities and then reclaim their areas. When large volumes of fine-grained soils are involved, the dredging is usually carried out hydraulically. Adopting this technology, the soil is transported as a slurry and deposited in containment facilities, where it initially sediments at high void ratios before experiencing great deformations during consolidation. The paper presents a numerical model able to simulate the distinctive features of this class of boundary value problems. The soil behaviour was modelled adopting the Modified Cam-clay model, in conjunction with a strongly non-linear void ratio:permeability law. The gradual filling of the containment facility was modelled by generating the whole soil column and then progressively applying gravity to each element. The model was tested simulating a challenging and well-documented case study. The comparison between numerical results and monitoring data confirms the effectiveness of the developed model and remarks its usefulness both at the design stage and during works.

A. de Lillis, G. M. Rotisciani, S. Miliziano

Influence of Soil Heterogeneity on the Selection of Input Motion for 1D Seismic Response Analysis

The availability of easily accessible databases of earthquake records allows the use of large sets of accelerograms for dynamic analyses of geotechnical systems. However, the selection of acceleration records is influenced by multiple sources of uncertainty related also to the geotechnical properties of the soil deposit which strongly affect the site seismic response. The authors recently proposed a procedure for a proper selection of the input ground motion to be used in 1D seismic site response analyses. An application of the procedure is presented and discussed in the paper highlighting the relevant influence of soil heterogeneity on the results of the accelerograms selection procedure.

F. Genovese, D. Aliberti, G. Biondi, E. Cascone

Hydro-Mechanical Behaviour of a Sand-Bentonite Mixture for the Confinement of Nuclear Wastes

The established concept for the protection of the biosphere from high-level nuclear wastes consists in the use of multi-barrier systems in deep geological repository, for which clayey geomaterials are key elements. Bentonite-based materials are selected as buffer and backfilling materials. Once in place, the barriers will be subjected to a series of severe loadings, including strong variations of suction (i.e. wetting and drying cycles). The paper presents selected results from a large ongoing research work to investigate the behaviour of bentonite-based materials in the context of nuclear waste disposal. In particular, the paper focuses on the response of a Sand/Bentonite mixture under different hydro-chemo-mechanical loadings. Performed experiments include free and confined swelling tests and controlled-suction confined swelling tests, along with an assessment of the fabric evolution during those loadings. Different dry densities and waters of different salinity were considered in the experiments. The obtained data combined with results from other studies allowed to define a trend for the calculation of the swelling pressure as a function of the relative dry density of the bentonite in the mixture.

A. Ferrari, D. Manca, L. Laloui

Numerical Study of Laterally Loaded Pile in Unsaturated Soils

This note presents the preliminary outcomes of a numerical investigation on the influence of soil partial saturation on the behaviour of laterally loaded piles. The modified Cam clay model extended to unsaturated conditions and formulated in terms of Bishop’s effective stress has been used to analyse the results of centrifuge tests designed to address this topic. The model, calibrated on laboratory tests, well reproduces the main aspects of the soil-pile interaction. Load-deflection relationships and bending moments are analysed together with soil reactions against the pile and the strength mobilization level in the soil. The paper points out the significant changes in the pile response given by any variations in soil saturation conditions.

L. M. Lalicata, G. M. Rotisciani, A. Desideri, F. Casini, L. Thorel

Use of Alkali-Activated Fly Ashes for Soil Treatment

The use of alkali-activated fly ashes (AAFA) to improve engineering properties of clayey soils is a novel solution, alternative to the widely diffused improvement based on the use of traditional binders such as lime and cement. An experimental investigation on chemo-physical evolution of alkali-activated binders and their use for soil improvement has been developed. Treated samples were prepared by mixing soil and fly ash with water and alkaline solution and dynamically compacted. Mechanical behaviour has been investigated by means of triaxial tests performed on treated samples compacted at optimum water content. Addition of alkali activated binder increased stiffness and shear strength of treated samples, whose extent depends on binder content and curing time.

Enza Vitale, Giacomo Russo, Dimitri Deneele

Lessons Learnt from the SS 106 Jonica Highway Construction Works

During the construction of a new highway segment in the hilly territory of the Calabria region, in South Italy, several instability processes have been activated so delaying the works and causing a cost increase of the infrastructure. Building an infrastructure in structurally complex clayey formations, so widely spread over the entire construction area, is certainly cumbersome; the highly tectonized clayey formations can hardly be characterized and their discontinuity patterns, often masked by the complexities of the geological features, make the instability phenomena difficult to foresee through standard practice investigations. Nevertheless, the risk of instability may be minimized if design strategies that resulted successful in similar conditions are implemented. In this paper such design strategies, to be adopted for excavations and earthworks in geologically complex soil formations, will be presented and analysed in the light of their economic and environmental sustainability, through the discussion of few case studies.

Paolo Ruggeri, Viviene Marianne Esther Fruzzetti, Giuseppe Scarpelli

Lightweight Cemented Soils: Mix Design, Production and Control

Development and validation of new technological methods for soil improvement in earthwork, allowing the reuse of excavated soils, are fundamental challenges in the framework of a sustainable geotechnical engineering design. Employment of natural soils not suitable for construction purposes to produce lightweight cemented soils represents an increasingly innovative technology. Lightweight cemented soils, obtained by adding air foam to soil-cement-water mixture to have a low density and self-levelling fresh mixture, are advantageously used for different earthworks, such as cavities filling, trench backfilling, embankment construction. The reuse of soil onsite, whose disposal normally significantly affects the overall construction costs, represents a clear environmental and economic advantage. In this paper a study on mix design for lightweight cemented soils is presented, highlighting the main effects of foam addition on physical and mechanical properties on different raw soils, based on experimental evidences. With reference to a case study (filling of an anthropic cavity in Piano di Sorrento, Italy), the effects of placement on lightweight cemented soils initial state are also addressed. A comparison in terms of physical and mechanical properties between material made in laboratory and sampled on site from the filling is shown. Furthermore, the role of construction controls and environmental conditions during placement on the relevant material parameters is highlighted.

Domenico De Sarno, Enza Vitale, Marco Valerio Nicotera, Raffaele Papa, Giacomo Russo, Gianfranco Urciuoli

Soil Stabilization Against Water Erosion via Calcite Precipitation by Plant-Derived Urease

Stabilization is often necessary to improve the stiffness, strength and durability of both natural and compacted soils. Soils are typically stabilized via the addition of hydraulic binders, such as cement and lime, which present however relatively high carbon and energy footprints. Alternative stabilization techniques are therefore explored to minimize environmental impact while preserving good material properties. Among these techniques, enzyme induced calcite precipitation (EICP) has gained prominence in recent years. EICP exploits the action of the urease enzyme to catalyze the hydrolysis of urea and to produce carbonate ions, which then react with calcium ions inside the pore water to cause precipitation of calcium carbonate (i.e. calcite). The precipitated mineral bonds particles together, thus improving the hydro-mechanical characteristics of the soil. This paper presents a preliminary investigation on the use of plant-derived urease, instead of pure reagent-grade urease, to minimize environmental and financial costs. The urease enzyme is obtained from a liquid soybeans extract, inside which urea and calcium chloride are dissolved. This stabilizing solution is then mixed with a silty clay to produce stabilized samples, which are subjected to water erosion tests.

Alessia Cuccurullo, Domenico Gallipoli, Agostino Walter Bruno, Charles Augarde, Paul Hughes, Christian La Borderie

Insights into the Behaviour of Energy Piles Under Different Head Constraints and Thermal Loads

The implementation of energy foundations complies with the directives of governments about increasing the use of renewable energy sources in the building sector. However, the current design of energy foundations relies more on common practice, based on ideal simplified working conditions, than on specific standards. The uncertainties about the role of various key factors on the mechanical response of the foundation still hinder the confidence in the practice. In this context, the numerical study presented in the contribution highlights the effects of different energy pile head constraints and thermal load histories, in the transient and steady state conditions. The importance of considering the pile head stiffening given by a building slab and the actual thermal load rate is pointed out by discussing the thermally induced axial forces, vertical displacements and shaft stresses. The assessment of the effects of these working conditions can improve the prediction accuracy, thus contributing to gain confidence at the design stage.

Donatella Sterpi

Bearing Capacity of Foundations Under Highly Eccentric Loads

In the case of wind turbines the eccentricity of the loads at foundation level is generally very high and very often the application point of the vertical load falls outside the core of the foundation. In the paper, two types of foundation of a tall wind turbine under highly eccentric loads are considered and designed: a shallow foundation and a pile group foundation. The design of the shallow foundation is based on the requirement of bearing capacity and on the allowable rotation for a safe operation. On the contrary, for pile groups the main design requirement is to avoid a bearing capacity failure, since the rotation limitation at foundation level is usually ensured by the high rotational stiffness of the group. Widespread practice for pile groups design is to consider the achievement of the axial capacity (in compression or in uplift) on the outermost pile as the ultimate limit state of the pile group. This approach neglects the ductility of the foundation system and therefore is uselessly conservative. A recently proposed and more efficient approach for the evaluation of ultimate moment-axial force interaction diagrams for a pile group is applied, and comparison with the design of a shallow foundation is presented.

Luca de Sanctis, Rosa M. S. Maiorano, Valeria Nappa, Stefano Aversa

Backmatter

Additional information