International Journal of Geomechanics

The cone penetration test (CPT) is used as a complementary approach for determining the bearing capacity of piles. Via direct CPT methods for pile capacity prediction, correlation coefficients smaller than unity are used to relate cone tip resistance and sleeve friction to pile toe and shaft capacities, respectively. For correlating CPT data to pile capacity, specific factors must be considered, such as diameter, penetration rate, partial embedment of pile toe into a hard layer, mechanism of plunging, failure zone, data processing, and stress–strain conditions. The aim of this paper is to investigate the role and significance of scale effects to establish a direct relation between CPT records and pile shaft capacity. A database has been compiled including 83 full-scale pile load tests and CPT records in order to calibrate and validate the proposed approach. The less-than-unity ratio of pile shaft capacity to cone sleeve friction (i.e., r_s/f_s) for most of the cases shows that shear stress in the soil surrounding the pile is smaller than in the soil around the cone. Therefore, the differences between pile and penetrometer penetration rate and geometry are considered as the major factors that cause lower shear strain in the soil around the pile. By considering the determinants, an analytical-practical procedure is proposed, from which the pile shaft capacity can be predicted using cone sleeve friction. This approach demonstrates better agreement with measured capacity by static loading test results (R_s) and less scatter than other current CPT methods, and it can be used as a complementary approach for determining pile shaft capacity.

In this paper, a pore-scale multiphase, multicomponent Shan–Chen model with proper pressure boundary scheme is developed and implemented to model binary flows in porous media, which enables us to reveal the displacement mechanism of binary flows in hydraulic fractures filled with proppant of different sizes. Each fluid is represented by a lattice with different particle distribution functions. The pressure boundary scheme should be carefully approached to avoid numerical instabilities, because two interrelated lattices coexist in the same computational domain. The present model is validated and calibrated by the bubble test and the static contact angle test. In addition, based on this model, the two-component displacement is investigated, which is of great importance to the petroleum industry CO₂ sequestration, subsurface energy storage, and waste landfill,. It involves complex flow mechanism affected by a variety of factors. In this study, only two factors are considered and studied: the wettability of binary fluids and the pore structures of propped fractures obtained from our previous studies. To evaluate the displacement performance in detail, three evaluation parameters, including breakthrough time, displacement efficiency and interfacial instabilities, are calculated in this simulation. Results show that both wettability and pore structures of propped fractures influence significantly the two-component displacement. The results agree qualitatively with the previous results, validating the effectiveness of the present model in predicting binary flows in propped fractures.

The pull-off test (POT) is a tensile strength testing method that is widely used in concrete/mortar and was recently applied to rock mechanics. The POT can be easily performed in both the field and the laboratory. This study uses the extended finite-element method to analyze the POT fracture mechanism under different test conditions and to assess the factors influencing the tensile strength of homogeneous rock. The numerical results were validated with experimental data, and a good agreement was obtained. An ideal test geometry was proposed (the depth and the width of the partial core were 2.5 and 0.4 cm, respectively). The POT can overestimate or underestimate the tensile strength of the rock, depending on the cohesive fracture energy, and a correction equation was proposed for visually homogeneous rocks and concrete.

Severe land subsidence caused by groundwater exploitation is one of the anthropogenic environmental problems. Even when groundwater exploitation has been limited or prohibited in some areas, it will continue in some water-deficient areas for a long time. Therefore, it is a challenge to reasonably exploit groundwater and not to cause severe land subsidence. A physical model test was conducted in this paper to simulate the extraction and recharge of groundwater, and to observe the soil deformation characteristics and the change of the pore water pressure. Based on the test results, the mechanism of land subsidence was investigated and different pumping modes were involved including the single-well pumping, single-well pumping and recharging, and double-well pumping and recharging tests. The tests indicated that the sand layer and clay layer had different pore water pressure change and deformation characteristics. In the sand layer, the pore water pressure decreased when pumping and increased when pumping stopped. In the clay layer, however, pore water pressure first increased rapidly and then decreased when pumping, and it decreased rapidly and then increased after pumping stopped. The variation of pore water pressure in the clay layer was consistent with the Mandel’s effect and was related to the distance to the pumped layer. The further the distance was, the longer the Mandel effect lasted. The sand layer mainly exhibited elastic deformation and the clay layer almost exhibited plastic deformation. The clay layer showed clear hysteresis. The hysteresis time was increased with the distance from the pumped sand layer. In addition, the results indicated that the three pumping modes could reduce land subsidence. With regard to the pumpage and land subsidence, the double-well pumping and recharging mode was better than the other two. With pumping or pumping and recharging together, the increasing rate of vertical displacement became smaller and gradually reached a stable state. In general, these three modes were reasonable for groundwater exploitation, and could effectively control land subsidence.

In most geotechnical construction works, compacted soils of cohesive-frictional nature are expected to remain mostly under partially saturated conditions and hence experience continuous changes in the suction state (negative pore-water pressure) stemming from seasonal weather and temperature variations throughout any given year. Over the last decade, a few studies have demonstrated that the suction stress characteristic curve (SSCC) can be used to describe the state of stress in partially saturated soils and therefore assess, with reasonable accuracy, the additional shear strength contribution resulting from matric or total suction. However, limited experimental data are available to conclusively verify the magnitude of suction stress at rather high values of suction, especially well beyond the residual suction. In the present work, the SSCC for compacted silty sand has been thoroughly assessed in light of recent experimental data obtained from suction-controlled triaxial testing over a wide range of matric and total suction values (0.05–300 MPa). The suction stress in the test soil was observed to increase with increasing suction even beyond the residual suction state, in contrast with findings from previous works reported in the literature for predominantly sandy or clayey soils. In addition, experimental data from suction-controlled true triaxial, ring shear, and plane strain (biaxial) tests, recently conducted on six different types of cohesive-frictional soils in the low-to-medium matric suction range, were also analyzed to obtain the corresponding SSCCs. Finally, suitable model equations are presented in order to best fit the multiple experimental data sets and hence predict the SSCC for each of the test soils under the different suction-controlled testing techniques.

This study employed finite element limit analysis (FELA) to investigate the influence of eccentric loads on the bearing capacity of footings above single and double continuous voids. Upper bound theorem (UB), lower bound theorem (LB), and adaptive meshing techniques were used in a parametric study to investigate the influence of some factors, including the relative distance between double voids, the depth of voids, the geometry of voids, the variation of soil shear strength, and the eccentricity of loadings on the bearing capacity of footings. The results indicated that, for the footings inclined above a single void, the bearing capacity with a void located on the same side of the eccentric load was less than that in an opposite position. In addition, the failure mechanisms were summarized and analyzed in this study.

Polymer antiseepage walls have advantages over conventional antiseepage walls in terms of environmental protect and construction convenience. Therefore, it is widely applied in seepage-proofing, reinforcement projects in earth dams. Aimed at better understanding the seismic performance of the new polymer antiseepage wall, appropriate research on the seismic behavior and seismic resistance analysis of an earth dam with the new antiseepage wall were conducted by using a centrifuge modeling test and certain verified numerical simulation. For comparison, the earth dam with a conventional concrete antiseepage wall was also included in the research and analysis. The results show the polymer antiseepage wall is superior to the concrete antiseepage wall in terms of acceleration resistance, dynamic stress response, and compatible deformation capacity. During a 0.4g earthquake, the overall seismic performance of an earth dam with a polymer antiseepage wall is also good.

The time-dependent hydromechanical behavior of rocks is crucial to assessing the long-term stability of rock engineering, such as reservoir rock slopes and underground waste storage facilities. This research aims at developing a discrete-element method (DEM)-based numerical method to simulate the whole water-induced carbonate rock failure process, which is highly sensitive to water with a maximum 70% loss of mechanical strength when saturated by water. First, strength degradation laws for carbonate rock induced by water were derived based on the different behaviors of two types of cement inside the rock. The degradation laws were coupled with universal distinct element code (UDEC) to build the progressive damage model by developing a customized code using Fish language. Numerical simulations were then carried out on laboratory-scale tests and an example of an engineering-scale rock slope. In laboratory-scale simulations, the predicted lifetime (time-to-failure) of the rock sample generally aligns with that of experimental results, and well-known physical phenomena, such as the pattern of macroscopic fracture and stress–strain responses, can also be reproduced. In the engineering-scale simulation, the long-term (nearly 5 years) progressive failure of the slope toe under the influence of the fluctuation reservoir level, and the consequent rockslide can be well modeled. The results indicate that the proposed model is capable of predicting the strength properties for carbonate rocks submerged in water for different time periods, as well as simulating the whole failure process of rock from the engineering scale due to water erosion.

The influence of perturbation magnitude and extent of area on the emergence of localized instability in sand specimens subjected to biaxial loading has been explored within a numerical framework using a generalized 3D material model. In this regard, this article seeks to examine the effect of perturbation type in terms of material imperfection and subsequently attempts to characterize mesh dependency on localization onset in sands. Coupled undrained transient (globally undrained locally drained) analysis of Hostun RF sand has been performed to investigate the onset of instability by inducing material heterogeneity within the numerical model considering small strain formulation. For a given magnitude of perturbation, it is observed that instability onset requires a specific mesh convergence study, and with mesh refinement it practically becomes asymptotic to the theoretically predicted value estimated by bifurcation analysis. Perturbation magnitude significantly influenced onset strain of instability when compared with the effect of extent of the area for a fixed perturbation magnitude. However, all the sand specimens revealed emergence of localized instability modes in both cases.

High-filled cut-and-cover tunnels (HFCCTs) are common in northwestern China because their construction allows usable land over the CCT to be reclaimed. However, due to the unique landforms of the Loess Plateau in this region of China, the amount of backfill soil that is needed for HFCCTs is enormous, and the backfill must be high enough to maximize the usable land. Currently, the main challenges for the construction of HFCCTs are ultrahigh earth pressure and safety concerns related to the existing CCT lining structure. This paper discusses physical modeling tests that were conducted to investigate (1) load reduction methods that utilize expanded polystyrene (EPS) in the backfill soil; and (2) structural modifications to CCTs. The experimental results agree well with the numerical analysis results. The numerical analysis helped to determine suitable thicknesses of EPS material for load reduction when the CCT was subjected to different backfill heights. Also, by modifying the cross-sectional shape of the lining structure of CCT, the internal forces could be altered to make the concrete structure support more compressive loads rather than succumb to bending moments. This study found that the coupled effects of load reduction using EPS and cross-sectional modifications of the CCT lining structure can significantly reduce the required thickness of the CCT lining structure, enhance the safety of the CCT, and increase the allowable backfill height.

Discontinuous deformation analysis (DDA) has gained wide acceptance in geotechnical engineering. The simulation of large-scale engineering problems using DDA is computationally expensive. Thus, improving the calculation efficiency of DDA is of significance. The parallel technique based on open multiprocessing (OpenMP) is implemented into DDA. Previous work usually focused on one or two specific subroutines. In contrast, in this paper, all the time-consuming subroutines that have the possibility to do the calculation simultaneously, including contact detection, matrix assembly, simultaneous equation solver, postjudgment of contacts, and block information update, are modified and incorporated with parallel implementation based on OpenMP. The parallel degree can be up to 98%. The computational efficiency of the accelerated DDA is demonstrated by several large-scale simulations with different block quantities running on a different number of threads. As an application, the accelerated DDA is used to efficiently analyze a large-scale landslide, which can efficiently provide information for landslide disaster prevention and mitigation. In conclusion, the accelerated DDA exhibits high performance in the analysis of large-scale problems.

This paper presents a generalized plastic mechanics–based constitutive model for the estimation of dynamic stresses in unsaturated subgrade soils under repeated vehicle loading conditions. The stresses in subgrade soils are taken as the sum of two components: dynamic stress and total suction. The increment of dynamic stress consists of three subcomponents, including coaxial stress increment, stress increment due to rotations of principal stresses under vehicle loading, and stress increment due to stress accumulation under repeated loading. The total suction in unsaturated subgrade soils is considered to comprise two subcomponents: wet suction characterizing the capillary effect between liquid and solid phases; and structure suction quantifying the adsorptive and bonding effects between soil particles. The proposed dynamic model is then solved using the numerical nonlinear incremental calculation method. A case study is presented in the end to elaborate on the application of the proposed model in practice. The calculated stresses in subgrade soils using both the proposed model and the conventional equivalent static load model are compared against the measured values in the field. Through the case study, the advantages and the practical value of the proposed model are demonstrated.

Borehole deviation is a common problem in anchor cable engineering of soil and rock, especially in long drilling holes, which affects the reinforcement effect of tension-type anchor cables, but the law of stress distribution and load transfer of anchorage section with borehole deviation is still not systematic or comprehensive. The research presented in this paper established an analytical model to determine the axial force and shear stress distribution and load transfer of linear and bending anchorage sections by using elastic mechanical analysis. A comparison of axial force and shear stress distribution and load transfer mechanic behavior of linear and bending anchorage sections was made, and the effects of tensile loading, anchorage segment lengths, bending radius and borehole diameters were calculated and analyzed. In addition, an indoor model test was carried out to validate the theoretical calculated results. The results from the theoretical analytical model and the indoor model test had good consistency, which indicated that: (i) the decay speed of axial force and shear stress on the bending anchorage sections was slower than on the linear ones, so a longer anchorage section length (about 23%) was needed when borehole deviation occurred in soil and rock engineering; (ii) the tensile loading, anchorage segment lengths, bending radius, and borehole diameters affected the axial force and shear stress values, reasonable stress distributions, the inner- and outer- surfaces ratios or all of these mechanic behaviors. The deduced analytical model can be used to calculate and predict the mechanic behavior of stress distribution and load transfer of linear and bending anchorage sections in anchor cable engineering.

Since previous studies give little consideration to the influence of different intermediate principal stresses in the cavity contraction problem, the unified strength theory (UST) is introduced into cylindrical cavity contraction. A closed-form unified equation for the large deformation of cavity contraction considering the influence of different degrees of the intermediate principal stress coefficient b is derived and verified by comparison with the existing solution based on the Mohr–Coulomb criterion. This analysis shows that consideration of intermediate principal stress can reduce cavity contraction, the essence of which is that introduction of b leads to an increase in the critical yield pressure and makes elastoplastic (EP) boundary moving towards the cavity wall. Parametric analysis shows that the influence of the intermediate principal stress on the radial displacement of the cavity is not negligible while its influence on the radial stress can be neglected; the greater the intermediate principal stress coefficient b is, the smaller the plastic zone around the cavity; the effect of the intermediate principal stress cannot be ignored when the soil stiffness is small or the dilation angle is large, and vice versa. The proposed solution through introduction of large deformation and intermediate principal stress coefficient b quantifies the influence of the intermediate principal stress on the cavity unloading–contractions relationship and can model the cylindrical cavity contraction behavior in drained or “dry” soil conditions in elastic-perfectly plastic geomaterials.

Prior laboratory and in situ investigations show that monotonic preshearing can have a significant effect on the cyclic response of granular materials. The underlying mechanics that are responsible for these changes in behavior in response to preshearing are not well characterized, however. Herein, we use the discrete-element method (DEM) to simulate undrained monotonic and cyclic simple shear tests with the constant volume method. Through published comparisons to laboratory data, DEM simulations have been shown to reasonably predict the cyclic response of granular materials, making them an appropriate tool for studying the effects of initial static shear stress on liquefaction initiation. Mechanical coordination number and the normal force-weighted fabric tensor are used to describe the evolution of fabric after monotonic preshearing and during cyclic loading. We find that higher initial static shear stress induces smaller cyclic strength in stress-controlled cyclic simple shear tests, but that there is no such effect in strain-controlled cyclic simple shear tests in which the normal force-weighted anisotropy is removed in the first three loading cycles. In addition, the stability of specimens is found to be closely related to pore-pressure increases. Finally, we show that the effect of initial static shear stress on liquefaction resistance is a combination of reduced stability before cyclic loading and accumulated shear strain during cyclic loading.

The solidification of construction waste slurry draws much attention today due to the increasing awareness of environmental protection. Magnesium oxychloride cement (MOC) was first incorporated to solidify slurry in combination with industrial residue, which has the potential to be used as roadbed material. Three types of binding materials including MOC, industrial residue, and industrial residue modified MOC were proposed to evaluate their performance in the solidification of construction slurry with high water content. The unconfined compressive strength (UCS) and coefficient of permeability were investigated, taking into account factors including MOC content, molar ratio of MgO/MgCl₂, mass ratio of MOC to industrial residue, industrial residue content, and curing time. The microstructure was identified to reveal the intrinsic mechanisms by scanning electron microscopy (SEM). The results showed that the mechanical behavior of solidified slurry was largely influenced by these factors, and the industrial residue proved effective in improving the strength and permeability of MOC solidified slurry by impeding the decomposition of phase 5 and phase 3 and absorbing a certain amount of water. The industrial residue modified MOC solidified slurry showed higher water resistance and a lower coefficient of permeability due to the generation of amorphous calcium silicate hydrate (C-S-H) gels, phase 5 and phase 3 that could form a much stronger interlocking network.

The role of underground metro tunnels in a modern urban society is indispensable. Nowadays, these populous metro tunnel networks are becoming a prime target for terror strikes around the world. Considering these terror threats, it is crucial to study the vulnerability of tunnels when subjected to an internal explosion. This paper evaluates the vulnerability of underground metro tunnels exposed to an internal explosion using the explicit finite element (FE) method. The developed FE model has been validated with the field data reported in the literature for free-field blast wave propagation. Parametric studies were also carried out using the developed models to investigate the effect of lining material, lining thickness, lining shape, and type of surrounding of soil on the blast response of tunnels. A typical metro tunnel of 5.0 m internal diameter embedded at a depth of 9.0 m below the ground level is considered for the analysis. Numerical analysis shows that reinforced cement concrete (RCC) tunnels suffer severe damage when compared with the cast-iron tunnels. Box tunnels are extremely vulnerable to internal explosion when compared with circular and horseshoe tunnels. RCC tunnels embedded in medium dense sand are less vulnerable when compared with soft saturated clayey soil.

The dynamic weakening of rock is frequently observed when the rock is subjected to a series of repetitive impact loads. Sandstone is utilized in our experiment on the dynamic performance under impact loading. The split Hopkinson pressure bar system with a confining pressure device is used for the experiments. Observations on strain waves recorded by a transmission bar indicate that sandstone demonstrates an evident nonlinear response under impacting loads which accompany a dynamic weakening effect. To quantify the damage induced by impact loads, we introduce a damage factor to study the weakening degree induced by impact loading and determine that sandstone breaks when the damage factor exceeds 0.52. Detailed statistics on the broken characteristics of the explored sandstone samples show that the damage evolution mainly extends along the maximum shear stress face, thus resulting in shear failure. Based on nonlinear wave propagation theory, we determine a shock wave distance for the explored sandstone. Result shows that the shock wave distance is larger than the sample length. Moreover, from a uniaxial compression test on specimens after impact tests, we found that failure patterns develop from split failure to shear slip failure with the increase in damage factor. Moreover, experimental observations comprise numerous dynamic regimes which can be extended to other granular rocks.

In the Jennings criterion, which is commonly used to estimate the shear strength of nonconsecutive jointed rock masses, the estimated values deviate from the actual values due to the criterion failure to consider the joint undulating angle and the weakening of the mechanical properties of the rock bridge during shearing. Based on the modified Jennings criterion, this paper considers the influence of normal stress and joint continuity on the degree of weakening of the rock bridge’s mechanical parameters and presents a new correction method to further modify the Jennings criterion. The collection of undisturbed rock samples from the study area and the creation of joint(s) for laboratory testing is a cumbersome task. To overcome these limitations, a methodology to simulate the failure of jointed rock mass using the rock-like material, cement mortar, containing a single joint was adopted and its details are presented in this paper. Specifically, the direct shear tests were conducted on artificially prepared jointed rock masses with different joint continuity and undulating angles. The influence of joint continuity and the undulating angle on the shear strength of the nonconsecutive joints was studied. Then, the influence of the normal stress and joint continuity on the deterioration of the mechanical properties of the rock bridge during shearing was analyzed based on the experimental results. A new model for estimating the shear strength of a nonconsecutive jointed rock mass was proposed based on the experimental results and previous studies. The test results show that the smaller the undulating angle and the greater the penetration, the lower the shear strength of the nonconsecutive joint. Besides, the normal stress level and the joint continuity have a significant influence on the weakening of the mechanical properties of the rock bridge. When the normal stress decreases or the joint length increases, the mechanical properties of the rock bridge are significantly weakened. Compared with our estimation of the nonconsecutive joint shear strength based on the original Jennings criterion and the modified Jennings criterion, the calculation results of the newly modified Jennings criterion developed in this study are generally more consistent with the measured values, and thus, they more accurately predict the shear strength of the nonconsecutive jointed rock mass with a regular joint undulating angle.

With unique advantages in simulating solid fracture, the combined finite–discrete-element method has become increasingly popular in the rock mechanics field. Nevertheless, a large number of microscopic parameters in the method need to be specified and many of them cannot be directly measured via laboratory tests. Therefore, these parameters must be determined via a calibration procedure. To calibrate appropriate microscopic parameters, we should find the relationship between them and the macroscopic mechanical response. In these microscopic parameters, the normal and tangential penalty parameters play a very important role. Thus, in this paper we study the effect of penalty parameters on macroscopic mechanical parameters in the combined finite–discrete-element method. It is found that as the penalty parameters increase, the elastic modulus and Poisson's ratio gradually approach the experimental values. However, the further increase of penalty parameters has little effect on the elastic modulus and Poisson's ratio when they reach 100 times the elastic modulus. Based on this conclusion, a simple method for the calibration of penalty parameters is proposed, which can be used to quickly determine the penalty parameters according to the uniaxial compression test.

The irrecoverable deformations in the substructure layers are detrimental to the track stability and demand frequent maintenance. With an escalation in axle load and traffic volume, the frequency of maintenance operations has remarkably increased. Consequently, there is an inevitable need to predict the long-term behavior of the track substructure layers. This article presents a methodology to evaluate the recoverable and irrecoverable responses of the substructure layers under the train-induced repetitive loads. The present method utilizes an integrated approach combining track loading, resiliency, and settlement models. The track substructure layers are simulated as lumped masses that are connected by springs and dashpots. The method is successfully validated against the field investigation data reported in the literature. A parametric study is conducted to investigate the influence of substructure layer properties on the track response. The results reveal that the response of each track layer is significantly influenced by the neighboring layer properties and the incorporation of multilayered track structure enables more accurate prediction of track behavior. The present analytical approach is simple, computationally efficient and may assist the practicing engineers in the safer design of the ballasted track.

In this study, a novel servocontrolled direct shear test set-up is proposed for testing of both intact and jointed rocks, and direct shear tests under different conditions were applied on intact sandstone samples and artificial joint samples. A three-dimensional (3D) laser-scanning profilometer system was employed to detect fracture surfaces and obtain the data of point clouds. Also, the anisotropic characteristics of the fracture surfaces were discussed based on data in variograms. Results revealed that crack initiation and propagation were affected by normal stresses in terms of path and mode. Based on the morphology of sheared fracture surfaces, the processes of crack initiation and propagation during shear failures were investigated. Two parameters (C and a) in the variogram were employed to quantify the anisotropy of fracture surfaces: the sill (C) reflects the height of the fluctuation body in fracture surfaces and the range (a) reflects the single fluctuation body and its fluctuation frequency. Additionally, a novel peak shear strength criterion was developed based on anisotropy indexes and it exhibited improved accuracy. Hence, it is concluded that the proposed model is superior to various conventional models.

The state parameter (ψ) measures the distance from the current state to the critical state line (CSL) in the compression plane. The existence of a correlation between both the peak angle of shearing resistance $({\varphi }_p^{\mathrm{\prime }})$ and peak dilatancy and ψ is central to many constitutive models used to predict granular soil behavior. These correlations do not explicitly consider particle crushing. Crushing-induced evolution of the particle size distribution influences the CSL position, and recent research supports the use of a critical state plane (CSP) to account for changes in grading. This contribution evaluates whether the CSP can be used to calculate ψ and thus enable the prediction of the peak angle of ${\varphi }_p^{\mathrm{\prime }}$ and peak dilatancy where crushing takes place. The data considered were generated from a validated DEM model of Fontainebleau sand that considers particle crushing. It is shown that where ψ is calculated by considering the CSL of the original uncrushed material, there can be a significant error in predicting the material response. However, where the CSP is used, there is a significant improvement in our ability to predict behavior irrespective of whether the CSP is accurately determined using a large number of tests or approximated using crushing yield envelopes. It is shown that the state parameter calculated using the previously available definition can give a false sense of security when assessing the liquefaction potential of potentially crushable soils. This contribution also highlights the stress-path dependency of the relationship between ${\varphi }_p^{\mathrm{\prime }}$ and ψ whichever approach is used to determine ψ.

Creep often occurs in tunnels excavated in soft rocks and it poses a risk to the long-term stability of the excavation. To derive measures for the effective mitigation of the risk, it is important to understand the time-dependent damage mechanism governing the deformation behavior of the surrounding rocks. A new creep constitutive model for soft rocks was proposed in this study to help achieve this understanding. The new creep model was developed based on the disturbed state concept, for example, the relatively intact state of rocks was described by the Burgers model and the fully adjusted critical state was represented by the generalized Bingham model. The analytical solution from the proposed model was given and the parameter calibration based on uniaxial compression creep experimental results were described. The deformation estimated by the proposed model was demonstrated to be in better agreement with experimental data than that estimated by the Burgers model alone. In addition, a three-dimensional creep constitutive model was proposed based on the one-dimensional form with the assumption of the constant bulk modulus. A case study for a tunnel with extensive time-dependent deformations was conducted using FLAC3D with the incorporation of the proposed three-dimensional creep model. The results indicated that the proposed creep model performed well in the prediction of the time-dependent deformations and failures in the section of the tunnel being studied. This model provided a very useful tool for engineers when determining the design for excavations and ground support schemes for tunnels in soft rocks where significant creep behaviors must be considered.

Over the past decades, stiffened slab foundations have been assessed as the most successful foundation system for structures that are susceptible to risks from reactive soils. However, most existing design methods simplify the complex three-dimensional (3D) moisture flow into a two-dimensional (2D) problem, which poses inevitable deformation incompatibility between soil mounds and footings. This paper proposes a design method based on advanced 3D finite-element (FE) coupled flow-deformation and stress analysis using a realistic seepage process, thereby mitigating the significant limitations associated with the available design methods. The paper presents the basic assumptions and necessary procedures of the proposed design method, along with detailed calibration and validation via an example that was also solved using a popular method, for comparison. The paper also uses the 3D modeling process to perform a comprehensive parametric study and produce a design tool based on a sophisticated artificial intelligence (AI) analysis using the evolutionary polynomial regression (EPR) technique.

With the development of infrastructure, new tunnel crossings below existing bridges are becoming increasingly common. This paper presents a case history of a shallow, double-line tunnel crossing below a bridge on a hillslope that was excavated using nonshield tunneling techniques. Due to poor geological conditions and unsymmetrical tunnel pressure, bridge stability is of great concern during tunneling. In addition to pregrouting the foundations of the bridge piers, selection of an appropriate construction scheme is essential. In this study, investigation of ground subsidence, bridge behavior, and an evaluation of bridge stability was carried out using the elastoplastic finite-element method (FEM) to model the excavation by three construction schemes: the ringlike drift-heading, center-diaphragm (CD), and cross-diaphragm (CRD) methods. Comparisons of ground subsidence and bridge deformation for the three construction schemes were made; monitored displacement data was also provided. Comprehensive analysis of the results indicated that the FEM gave a reasonable approximation of excavation-induced displacement and was able to discriminate the relative displacement-controlling capability of the three excavation methods. The CRD method demonstrated superior deformation-controlling capability and was ultimately adopted as the excavation method. The project was completed successfully, and no cracking was observed in either the piers or bridge deck during tunneling; the monitored displacements were larger than those calculated, which may be attributed to the excavation disturbance of the rocks. It is not easy to approximate discontinuous deformation by continuity-based FEM. This case history may serve as a reference for similar projects.

Natural slopes are often observed to have a concave, convex, or a combination concave/convex profile, yet constructed slopes are traditionally designed with planar cross-sectional geometry. In this paper, the stability of two planar slopes was compared with that of companion concave slopes, designed to have similar factor of safety (FOS) under gravity loading. The stability of these slopes was then investigated in response to a suction event followed by a precipitation event, and it was shown that both the planar and the concave slopes experienced similar changes in stability. Additional analyses were conducted with a simulated erosion mechanism to investigate how the planar and concave shapes would evolve under a sequence of three similar suction/precipitation/erosion cycles. The results suggest that for these slopes, the second and third simulated weather cycles reduced the stability of the slopes, yet had a lesser effect on the concave slopes than the planar slopes. This is in spite of the fact that the planar slopes became more concave-like due to the simulated erosion and suggests that slopes designed to be concave may perform better than the planar slopes.

Excess pore water pressure (EPWP) measurements taken at different positions on a penetrating piezocone into a clayey soil are believed to play an important role in correlating to its characteristics. On this subject, many correlations were proposed by several researchers, mainly empirically and mostly with EPWPs measured at the cone shoulder (u₂). The use of EPWP measurements at other positions, for example, behind the friction sleeve (u₃) has not been evaluated, possibly because of the lack of u₃ measuring elements for most penetrometers on the market. In this study, the piezocone penetration test in saturated intact clays was numerically modeled using finite element formulation. The EPWP distribution generated along the friction sleeve was investigated and it was found that the previously mentioned distribution closely followed an exponential trend which was mainly affected by the overconsolidation ratio (OCR) and the rigidity index (I_r) of the soil. Further investigations led this study to propose an innovative relationship to estimate u₃ values from measurements of common piezocone tests on the market (u₂-type) and pertinent soil characteristics. The well-predicting capability of numerical modeling procedures and the proposed relationship was compared with and validated with available experimental and field piezocone test measurements.

The moisture and heat fluxes in undeformable unsaturated porous media involve the movement of water, air, and heat that are induced by thermal and pressure gradients to which the porous medium is subjected under environmental conditions. Herein, the flow of the liquid phase is governed by the advective flow due to the hydraulic gradient and by the convective heat transfer due to the thermal gradient. The flow of the gas phase is governed by the advective flow due to the pressure gradient and the nonadvective flow of dry air and water vapor diffusion. The heat transport can be carried out by conduction, convection, and advection due to the pressure gradient. The mathematical model includes the air mass conservation, water mass conservation, and thermal energy conservation equations. This paper presents a detailed computational model based on the finite difference method (FDM) for one-dimensional analysis of the flow problem of heat and moisture in undeformable unsaturated porous media. Verification examples involving unsaturated flow analysis in isothermal and nonisothermal conditions are presented, highlighting the importance of having a relatively simple computational model to analyze a very complex physical problem.

In engineering constructions, the backfill behind retaining walls is usually narrow, and its boundary conditions are asymmetric due to the space limitation. When the retaining wall rotates about the bottom, the direction of the principal stress also rotates due to the granular properties of soil and the multiple interfaces friction. Such phenomenon is more significant in narrow backfill, however, there are few studies about this. The finite element method analysis is able to demonstrate how the failure mode of narrow backfill and the rotation of principal stress are affected by the backfill geometry and interfaces friction. Theoretical analysis is employed here to calculate the principal stress rotation angle and lateral pressure coefficient of the interface element. Similarly, active earth pressure of narrow cohesionless backfill against inclined rigid walls rotating about the bottom, considering principal stress rotation and uniform load on the ground, is derived by differential element limit equilibrium, which, upon comparison with methods used in previous studies, is suitable for the asymmetric inclined boundaries and improves the scope and accuracy of calculation. Parametric studies herein show that increasing the new structure inclination and decreasing its friction will reduce the interference in the existing structure.

Simulating large-scale problems are still challenging for discontinuous deformation analysis (DDA). To this end, this paper develops an efficient disk-based DDA (DDDA) model considering the efficiency in searching contact pairs and solving linear equations. First, an efficient contact search algorithm, namely the lattice search algorithm (LSA), is proposed, and efficiency tests of the LSA and direct search algorithm (DSA) demonstrate the high efficiency of the LSA. Second, three equations solvers, namely Jacobi iterative method (J), conjugate gradient method (CG), and preconditioned CG (PCG), are adopted to respectively solve the equations of the DDDA, and efficiency tests of these solvers show that the best solver is the PCG and the J is unsuited to solving the equations when using large penalty spring stiffness. Finally, a landslide simulation which includes 30,000 disks, 5,990 line segments, and 180,000 calculation steps is conducted, the result of which shows that: (1) up to 41.1 h, which is 99.2% of the time consumed in contact search using the DSA, is reduced by using the LSA; (2) up to 18.22 h, which is 69.8% of the time consumed in solving the equations using the CG, is reduced by using the PCG as the equation solver; (3) the time consumed in the simulation is 68.72 h when using the DSA to search contact pairs and using the CG to solve the equations; while the consumed time reduces to 9.4 h when using the LSA to search contact pairs and using the PCG to solve the equations, whose reduction proportion is 86.3%. The simulation indicates the large-scale computation capacity and further application in engineering with the DDDA.

For soil slopes susceptible to a potential failure, some preemptive measures in the form of reinforced structures are commonly adopted to improve stability. In this study, the seismic stability of a geosynthetic-reinforced soil slope is assessed by applying discretization-based kinematic analysis. Emphasis is placed on the consideration of earthquake input based on the pseudo-static, simple pseudo-dynamic, improved pseudo-dynamic, and modified pseudo-dynamic approaches. The reinforcement force required for maintaining a vertical soil wall is derived from the energy-based balance equation, and comparison between the solutions from these four approaches is highlighted. In order to yield a more reliable solution, a fully coupled pseudo-dynamic analysis is proposed in seismic slope stability assessment, which considers body and Rayleigh waves.

The physical and mechanical performances of coal, which does not just depend on the initial mineral composition and structure, are also dominated by the later engineering and geology environments, including high temperature, water saturation, and corrosive effect. In this paper, coal specimens, after high temperature treatment in an approximately vacuum environment, were conducted to the uniaxial compression, Brazilian split, scanning electron microscope (SEM) and mercury intrusion tests, respectively, to investigate the influence of temperature on the mechanical behaviors and pore features. The results showed that the mechanical parameters decrease gradually with an increase in temperature, presenting four stages: 25°C–200°C, 200°C–300°C, 300°C–400°C, and greater than 400°C. Increases in temperature also lead to the increase of porosity, together with the transformation of pore diameter, especially at 400°C–450°C because of the seriously thermal cracking and decomposition. Unexpectedly, due to the structure redistribution of mineral grains, from 450°C to 500°C, both the porosity and pore diameter show a drastic drop.

The limit equilibrium method (LEM) and the strength reduction method (SRM) are popular tools used for assessing the stability of slopes. However, they require complex numerical geomechanical models to be constructed and iterative computations to be performed. This study presents a rapid calculation method for the factor of safety of homogeneous and uniform slopes. First, the critical failure state curve is established to represent the relationship among all the parameters associated with slope stability, including the slope angle, slope height, unit weight, cohesion, and friction angle, when the slope is at the critical failure state. Second, based on the proposed critical failure state curve, an explicit expression is derived to directly provide the factor of safety for any homogeneous and uniform slope taking the soil Mohr–Coulomb parameters (i.e., cohesion and friction angle), unit weight, slope height, and slope angle as inputs. In contrast, once the soil's mechanical parameters are determined, for a given factor of safety, the slope height and angle may be calculated. Finally, the proposed method is applied to three cases to illustrate its applicability and validity. The results for all three cases show good agreement with those from the LEM software Slide 6.0.

Back-to-back mechanically stabilized earth (MSE) walls are commonly used in the construction of transportation infrastructure facilities. Federal Highway Administration (FHWA) guidelines discuss briefly the design of reinforced back-to-back walls. In this study, a numerical model was developed to study the behavior of connected and unconnected back-to-back walls under working stresses. The effect of reinforcement stiffness on tensile force profiles, the maximum tensile force developed in the reinforcement, and lateral pressures and lateral deformations for both unconnected and connected walls are discussed in detail. A well-defined critical slip surface was observed for the case of the unconnected back-to-back wall with relatively extensible reinforcement. Lateral pressures at the facing in both the cases were found to be almost equal, and the tensile forces developed in the reinforcement for the connected case were found to be uniform along the length of the reinforcement (except at higher depths).

Time-dependent deformation of crushable soils attributable to particle breakage could dominate the postconstruction stability of high rockfill dams and pile foundations. The evolutionary trends of the volumetric strain, particle-size distribution (PSD), and particle breakage of carbonate sands with 10% fines content for various loading durations and vertical stress levels are investigated by performing a series of one-dimensional compression tests. Loading durations ranging from 1 to 10,000 min, vertical stress levels ranging from 200 to 3,200 kPa, and fines content percentages ranging from 0 to 20 are considered. The results indicate that the increased loading duration in the initial stage has a significant effect on the volumetric strain; however, as the loading duration increases, this effect gradually decreases. In addition, the PSD curve shifts upward as the loading duration increases, indicating that the amount of particle breakage increases accordingly. Both the loading duration and the vertical stress can induce PSD changes in carbonate sands. Empirical equations are proposed to describe the relationship between the relative particle breakage index and the loading duration as well as the relationship between the relative particle breakage index and the vertical stress.

The stability of a tunnel face is described by the combined effects of surcharge load, self-weight of the soil, and internal supporting pressure. This combination can cause failure in either blowout or collapse. Since the plastic shearing in undrained soils is independent of loading directions in homogeneous soils, this paper studies Broms and Bennermark’s original stability number for the circular tunnel heading in cohesive soil using three-dimensional upper and lower bound finite-element limit analysis. Dimensionless ratios are used in this study to cover practical soil parameters and tunnel depths for collapse and blowout analyses. Numerical results of critical stability numbers are compared with two-dimensional and three-dimensional solutions available in the literature. Stability design charts and tables produced in this paper can be used to estimate safety factors for various design parameters.

This paper presents a coupled method of the analytical layer element and finite element for investigating the behavior of a pile group with a rigid cap in multilayered poroelastic soils due to a vertical loading. Each pile in the group is modeled as a one-dimensional bar by the finite-element method. Based on the analytical layer element solutions for the multilayered poroelastic soils, solutions for the interaction problem are obtained by incorporating the compatibility condition between the pile group and poroelastic soils. Numerical examples are provided to study the influences of the pile–soil stiffness ratio, pile length–radius ratio, soil stratification, and time factor on the time-dependent response of the pile group in multilayered poroelastic soils.