Within the framework of feasibility studies for a reversible, deep geological repository of high- and intermediate-level long-lived radioactive waste (HLW, IL-LLW), the French National Radioactive Waste Management Agency (Andra) is investigating the Callovo-Oxfordian (COx) formation near Bure (northeast part of France) as a potential host rock for the repository. The hydro-mechanical (HM) behaviour is an important issue to design and optimise different components of the disposal such as shaft, ramp, drift, and waste package disposal facilities. Over the past 20 years, a large number of laboratory experiments have been carried out to characterise and understand the HM behaviours of COx claystones. At the beginning, samples came from deep boreholes drilled at the ground surface with oil base mud. From 2000 onwards, with the launch of the construction of the Meuse/Haute-Marne Underground Research Laboratory (MHM URL), most samples have been extracted from a large number of air drilled boreholes in the URL. In parallel, various constitutive models have been developed for modelling. The thermo-hydro-mechanical (THM) behaviours of the COx claystones were investigated under different repository conditions. Core samples are subjected to a complex HM loading path before testing, due to drilling, conditioning and preparation. Various kinds of effects on the characteristics of the claystones are highlighted and discussed, and the procedures for core extraction and packaging as well as a systematic sample preparation protocol are proposed in order to minimise the uncertainties on test results. The representativeness of the test results is also addressed with regard to the in situ rock mass

Impact-induced damage to jointed rock masses has important consequences in various mining and civil engineering applications. This paper reports a numerical investigation to address the responses of jointed rock masses subjected to impact loading. It also focuses on the static and dynamic properties of an intact rock derived from a series of laboratory tests on meta-sandstone samples from a quarry in Nova Scotia, Canada. A distinct element code (PFC2D) was used to generate a bonded particle model (BPM) to simulate both the static and dynamic properties of the intact rock. The calibrated BPM was then used to construct large-scale jointed rock mass samples by incorporating discrete joint networks of multiple joint intensities into the intact rock matrix represented by the BPM. Finally, the impact-induced damage inflicted by a rigid projectile particle on the jointed rock mass samples was determined through the use of the numerical model. The simulation results show that joints play an important role in the impact-induced rock mass damage where higher joint intensity results in more damage to the rock mass. This is mainly attributed to variations of stress wave propagation in jointed rock masses as compared to intact rock devoid of joints.

Application of cemented rockfilling to underground mining could not be separated from the corresponding backfill's shear strength properties. The shear of cemented rockfill (CRF)-rock wall and the shear interaction occurring within CRFs both have some disadvantageous failure chances. In this study, we tried to investigate the complete shear properties of CRFs using direct shear and triaxial tests of cemented granite rockfill. Large-scale triaxial testing was held to accommodate the large CRF sample. Direct shear testing on the prepared flat and smooth surfaces was assessed with brief conversions and their corrections were used to approximate the shear strength envelopes of CRF joint interfaces. Two types of CRFs with the same aggregate size and distribution but different unconfined compressive strengths (UCSs) due to different mixture designs indicated insignificant differences between their basic friction angles, and also their asperity inclination angles. Nevertheless, investigation between direct shear test and triaxial test showed that the specimen with higher UCS tended to have a slightly lower friction angle but a higher cohesion than the other one.

In this paper, the Mohr-Coulomb shear strength criterion is modified by mobilising the cohesion and internal friction angle with normal stress, in order to capture the nonlinearity and critical state concept for intact rocks reported in the literature. The mathematical expression for the strength is the same as the classical form, but the terms of cohesion and internal friction angle depend on the normal stress now, leading to a nonlinear relationship between the strength and normal stress. It covers both the tension and compression regions with different expressions for cohesion and internal friction angle. The strengths from the two regions join continuously at the transition of zero normal stress. The part in the compression region approximately satisfies the conditions of critical state, where the maximum shear strength is reached. Due to the nonlinearity, the classical simple relationship between the parameters of cohesion, internal friction angle and uniaxial compressive strength from the linear Mohr-Coulomb criterion does not hold anymore. The equation for determining one of the three parameters in terms of the other two is supplied. This equation is nonlinear and thus a nonlinear equation solver is needed. For simplicity, the classical linear relationship is used as a local approximation. The approximate modified Mohr-Coulomb criterion has been implemented in a fracture mechanics based numerical code FRACOD, and an example case of deep tunnel failure is presented to demonstrate the difference between the original and modified Mohr-Coulomb criteria. It is shown that the nonlinear modified Mohr-Coulomb criterion predicts somewhat deeper and more intensive fracturing regions in the surrounding rock mass than the original linear Mohr-Coulomb criterion. A more comrehensive piecewise nonlinear shear strength criterion is also included in Appendix B for those readers who are interested. It covers the tensile, compressive, brittle-ductile behaviour transition and the critical state, and gives smooth transitions.

Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness.

Recently, a four-dimensional lattice spring model (4D-LSM) was developed to overcome the Poisson's ratio limitation of the classical LSM by introducing the fourth-dimensional spatial interaction. In this work, some aspects of the 4D-LSM on solving problems in geomechanics are investigated, such as the ability to reproduce elastic properties of geomaterials, the capability of solving heterogeneous problems, the accuracy on modelling stress wave propagation, the ability to solve dynamic fracturing and the parallel computational efficiency. Our results indicate that the 4D-LSM is promising to deal with problems in geomechanics.

A discrete element method (DEM) model was used to simulate the development of compaction-induced stress in a granular base course, with and without geogrid reinforcement. The granular base course was modeled as a mixture of uniformly sized triangular particles. The geogrid was modeled as a series of equally spaced balls that interact with each other through long-range interaction contacts. The long-range interaction contact was also used to simulate a deformable subgrade. The compactor was modeled as a solid cylinder rolling at a constant speed. The DEM model shows that the geogrid-reinforced granular base course gains additional compaction-induced stress due to the residual tensile stress developed in the geogrid. The residual tensile stress in the geogrid increases with the number of compaction passes. Parametric analyses were also conducted to assess the effects of geogrid stiffness and subgrade modulus on the compaction-induced stress.

When the pore pressure in a porous rock changes, stress arching will occur within the rock and the surrounding region. Stress arching ratio is defined as the total stress changes in the porous rock to the pore pressure change in the region. The region may have the same or different elastic moduli with the surrounding rock, which is usually referred to as inclusion or inhomogeneity. Stress arching is responsible for many geomechanical problems encountered during production or injection; in addition, it is a crucial parameter in stress estimation during field development. This paper aims to present laboratory measurements of vertical stress arching ratio in a material surrounding the inclusion (inhomogeneity). To the authors' knowledge, few laboratory experiments have been reported on direct measurement of stress arching. The inclusion is a cylindrical sandstone (44 mm in diameter and 50 mm in height) embedded in a larger cylindrical sandstone (150 mm in diameter and 154 mm in height), both of which are made synthetically. These two parts are separated and sealed by a internal polyurethane sleeve. Vertical stress changes are recorded by a mini hydraulic sensor embedded in surrounding rock. Laboratory results are compared to those obtained by numerical models. These models are checked with analytical formulations. The results of numerical models show a good agreement with laboratory data. The numerical results also indicate that the sensor response is affected by elastic properties of the internal sleeve. According to the sensitivity analysis performed, in the absence of the internal sleeve, properties of the inclusion have significant effects on the surrounding stress arching induced.

Engineering geological and hydro-geological characteristics of foundation rock and surrounding rock mass are the main factors that affect the stability of underground engineering. This paper presents the concept of multiscale hierarchical digital rock mass models to describe the rock mass, including its structures in different scales and corresponding scale dependence. Four scales including regional scale, engineering scale, laboratory scale and microscale are determined, and the corresponding scale-dependent geological structures and their characterization methods are provided. Image analysis and processing method, geostatistics and Monte Carlo simulation technique are used to establish the multiscale hierarchical digital rock mass models, in which the main micro- and macro-structures of rock mass in different geological units and scales are reflected and connected. A computer code is developed for numerically analyzing the strength, fracture behavior and hydraulic conductivity of rock mass using the multiscale hierarchical digital models. Using the models and methods provided in this paper, the geological information of rock mass in different geological units and scales can be considered sufficiently, and the influence of downscale characteristics (such as meso-scale) on the upscale characteristics (such as engineering scale) can be calculated by considering the discrete geological structures in the downscale model as equivalent continuous media in the upscale model. Thus the mechanical and hydraulic properties of rock mass may be evaluated rationally and precisely. The multiscale hierarchical digital rock mass models and the corresponding methods proposed in this paper provide a unified and simple solution for determining the mechanical and hydraulic properties of rock mass in different scales.

Similar to free-standing pile groups, piled raft foundations are conventionally designed in which the piles carry the total load of structure and the raft bearing capacity is not taken into account. Numerous studies indicated that this method is too conservative. Only when the pile cap is elevated from the ground level, the raft bearing contribution can be neglected. In a piled raft foundation, pile–soil–raft interaction is complicated. Although several numerical studies have been carried out to analyze the behaviors of piled raft foundations, very few experimental studies are reported in the literature. The available laboratory studies mainly focused on steel piles. The present study aims to compare the behaviors of piled raft foundations with free-standing pile groups in sand, using laboratory physical models. Cast-in-place concrete piles and concrete raft are used for the tests. The tests are conducted on single pile, single pile in pile group, unpiled raft, free-standing pile group and piled raft foundation. We examine the effects of the number of piles, the pile installation method and the interaction between different components of foundation. The results indicate that the ultimate bearing capacity of the piled raft foundation is considerably higher than that of the free-standing pile group with the same number of piles. With installation of the single pile in the group, the pile bearing capacity and stiffness increase. Installation of the piles beneath the raft decreases the bearing capacity of the raft. When the raft bearing capacity is not included in the design process, the allowable bearing capacity of the piled raft is underestimated by more than 200%. This deviation intensifies with increasing spacing of the piles.

This paper presents a reliability analysis of the pseudo-static seismic bearing capacity of a strip foundation using the limit equilibrium theory. The first-order reliability method (FORM) is employed to calculate the reliability index. The response surface methodology (RSM) is used to assess the Hasofer–Lind reliability index and then it is optimized using a genetic algorithm (GA). The random variables used are the soil shear strength parameters and the seismic coefficients (kh and kv). Two assumptions (normal and non-normal distribution) are used for the random variables. The assumption of uncorrelated variables was found to be conservative in comparison to that of negatively correlated soil shear strength parameters. The assumption of non-normal distribution for the random variables can induce a negative effect on the reliability index of the practical range of the seismic bearing capacity.

This paper presents the effect of open dumping of municipal solid waste (MSW) on soil characteristics in the mountainous region of Himachal Pradesh, India. The solid waste of dumpsite contains various complex characteristics with organic fractions of the highest proportions. As leachate percolates into the soil, it migrates contaminants into the soil and affects soil stability and strength. The study includes the geotechnical investigation of dump soil characteristics and its comparison with the natural soil samples taken from outside the proximity of dumpsites. The geochemical analysis of dumpsite soil samples was also carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Visual inspection revealed that the MSW consists of high fraction of organics, followed by paper. The soil samples were collected from five trial pits in the dumpsites at depths of 0.5 m, 1 m and 1.5 m. Then the collected soil samples were subjected to specific gravity test, grain size analysis, Atterberg's limit test, compaction test, direct shear test, California bearing ratio (CBR) test and permeability analysis. The study indicated that the dumpsite soils from four study regions show decreasing trends in the values of maximum dry density (MDD), specific gravity, cohesion and CBR, and increasing permeability as compared to the natural soil. The results show that the geotechnical properties of the soils at all four study locations have been severely hampered due to contamination induced by open dumping of waste.

This paper presents a model to simulate the monotonic and cyclic behaviours of weakly cemented sands. An elastoplastic constitutive model within the framework of bounding surface plasticity theory is adopted to predict the mechanical behaviour of soft sandstone under monotonic and cyclic loadings. In this model, the loading surface always passes through the current stress state regardless of the type of loading. Destruction of the cementation bonds by plastic deformation in the model is considered as the primary mechanism responsible for the mechanical degradation of loosely cemented sands/weak rock. To model cyclic response, the unloading plastic and elastic moduli are formulated based on the loading/reloading plastic and elastic moduli. The proposed model was implemented in FLAC2D and evaluated against laboratory triaxial tests under monotonic and cyclic loadings, and the model results agreed well with the experimental observations. For cyclic tests, hysteresis loops are captured with reasonable accuracy.

Despite of the limitation in modeling infinite space, the finite element method (FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometries, conditions and material behaviors. A kind of absorbing layer named perfectly matched layer (PML) has been applied to modeling the radiation damping using FEM, which makes the dynamic analysis of soil-structure interaction more accurate. The PML is capable of absorbing incident waves under any angle and frequency, ensuring them to pass through the model boundaries without reflection. In this context, a new FEM program has been written and the PML formula has been implemented by rewriting the dynamic equation of motion and deriving new properties for the quadrilateral elements. The analysis of soil-foundation interaction by applying the PML is validated by the evaluation of impedance/compliance functions for different ground conditions. The results obtained from the PML model match the extended mesh results, even though the domain is small enough that other types of absorbing boundaries can reflect waves back to the foundation. The mechanism of the wave propagation in the region shows that the forced vibrations can be fully absorbed and damped by the boundaries surrounded by PMLs which is the role of radiation damping in FEM modeling.

Recycling of industrial waste is one of the effective ways to overcome their disposal problem. Ash produced by thermal power plants and lime sludge produced by paper mills require huge disposal land and may create environmental problems such as dusting and leaching of harmful heavy metals. Stabilization of the ash can improve its engineering properties and address the environmental problems. This paper reports the laboratory test results of a Class F pond ash stabilized with lime (2%, 4%, 6% and 8% by weight) alone and in combination with lime sludge (5%, 10% and 15% by weight). The X-ray diffraction (XRD) and scanning electron micrograph (SEM) tests were also performed to identify the possible formation of crystalline phases after stabilization. The effects of lime sludge on the unsoaked and soaked bearing ratios of pond ash with different lime contents, after 7 d, 28 d and 45 d of curing, were observed. Test results indicated that the bearing ratio increased considerably up to a 4% lime content which can be taken as the optimum lime content. Further increase in lime content increased bearing ratio gradually but at a slower rate. The effect of lime sludge was more pronounced at the optimum lime content, particularly at a low curing period. Lime sludge improved the bearing ratio in soaked condition significantly. Leachate analysis of stabilized ash was performed using toxicity characteristic leaching procedure (TCLP-1311) method. The concentrations of toxic elements Zn, Cu, Cd, Ni and Cr in the stabilized mixes were lower than those in the unstabilized waste. The results indicated that the pond ash-lime-lime sludge mixes have potential application as road subbase material.

The original unified hardening (UH) model, in which a straight Hvorslev envelope was employed to determine the potential peak stress ratio of overconsolidated soils, is revised using a smoothed Hvorslev envelope (Hermite-Hvorslev envelope). The strength at the intersection between the straight Hvorslev envelope and the critical state surface (i.e. Mohr-Coulomb envelope) can be undefined due to the discontinuous change in the slope of the two linear strength envelopes mentioned above. A smoothed Hvorslev envelope is derived through Hermite interpolation to ensure a smooth change between the proposed Hvorslev envelope and the zero-tension surface as well as a smoothed transition between the proposed Hvorslev envelope and the critical state surface. The Hermite-Hvorslev envelope is then integrated into the original UH model, and then the UH models with four different functions of the Hvorslev envelope are compared with each other. The UH model revised by the Hermite-Hvorslev envelope can well predict the mechanical behaviors of normally consolidated and overconsolidated soils in drained and undrained conditions with the same parameters in the modified Cam-Clay model.

soil-cement is a mixture produced by grouting or mixing cement with soils. This paper reviews and discusses the general classifications of grouting techniques and the suitability of their applications. The mechanical properties of soil-cement mixture and the influence of sodium silicate added are discussed. Design considerations for deep soil mixed wall (DSMW) for excavation support and vault arch for tunnelling stabilisation are presented. Parameters for the numerical analysis of soil-cement mixture are evaluated and recommended.

Flexible catch fences are widely used to protect infrastructure like railways, roads and buildings from rockfall damage. The wire meshes are the most critical components for catch fences as they dissipate most of the impact energy. Understanding their mechanical response is crucial for a catch fence design. This paper presents a new method for testing the wire meshes under rock impact. Wire meshes with different lengths can be used and the supporting cables can be readily installed in the tests. It is found that a smaller boulder causes more deformation localisation in the mesh. Longer mesh length makes the fence more flexible. Under the same impact condition, the longer mesh deforms more along the impact direction and shrinks more laterally. Supporting cables can reduce the lateral shrinkage of the mesh effectively. Most of the impact energy is dissipated by stretching of the wires. Wire breakage has not been observed.