International Journal of Geomechanics

Large structures, such as offshore platforms, wind turbine foundations, wide buildings, bridges, and railway granular embankments, are often supported by pile foundations. These structures are usually subjected to large cyclic loads (in axial, lateral, and torsional modes) arising from actions of waves, ship impacts, or moving trains. Significant torsional cyclic forces can be transferred to the foundation piles due to the eccentricity of the lateral loads. In the past, several theoretical and experimental investigations were carried out on piles under axial and lateral cyclic loads; however, study of the influence of torsional cyclic loads on pile foundations is rather limited. This paper presents a novel numerical model based on the boundary element approach to analyze the response of a single, vertical, floating pile subjected to torsional cyclic load. The nonlinear stress-strain response of soil is incorporated, and the pile material was idealized as elastic-perfectly plastic. The effect of progressive degradation of soil strength and stiffness under cyclic stress reversal is incorporated in the numerical method. Apart from predicting the degradation of torsional pile–soil interactive performance, the profiles for shear stress and angle of twist are also captured by the proposed solution. Validation of the model indicates the suitability and accuracy of the proposed solutions. The frequency, amplitude, and number of cycles play significant roles in torsional cyclic response of piles. The proposed model is also applied successfully to selected case studies on single piles under torsional cyclic loading, and important conclusions are drawn from there.

In an unsaturated soil with desiccation cracks, the overall moisture-diffusion coefficient can be considered as consisting of two components, the diffusion coefficient of the intact (uncracked) soil matrix and the diffusion coefficient of the cracks developed during the desiccation process. Several models are available for obtaining the diffusivity of the intact soils, whereas the models considering the effects of cracks on the diffusion coefficient are either complex or insufficient. In this paper, a numerical model is presented to investigate the influence of the desiccation cracks on the moisture-diffusion coefficient of unsaturated soils. The analyses of the results indicate that the diffusion coefficient component, due to the desiccation cracks, dominates the overall diffusivity of the soil matrix, whereas the diffusion coefficient of the intact (uncracked) soil can be ignored for all practical purposes when the cracks occur. The main factor controlling the diffusion coefficient due to the cracks is the geometrical dimension of the cracks. Thus, the variation of the diffusion coefficient with the crack width and the crack depth is also evaluated. Unlike the diffusivity of an intact (uncracked) soil, which is nearly constant for a specific soil over a small suction change, the diffusivity of a cracked soil varies with depth due to the changes in the crack dimensions. Also, the effect of the cracks on the diffusion coefficient at shallow depths over a deep soil layer is limited and can be ignored when the depth reaches a specific value. Practical guidelines are provided to estimate the field diffusion coefficient when the crack width and depth are given.

Cantilever retaining walls are earth-retaining structures commonly used in construction. Conventional methods used to determine the active earth thrust acting on a wall often neglect friction between the soil and wall. This study presents an analytical solution for determining the active earth thrusts acting on a cantilever retaining wall with a short heel and a shear key that supports granular backfill. Three different earth thrusts were considered to be acting on three different parts of the rear face of the wall; the thrusts were derived using the limit equilibrium method. The active earth thrust formulas were also simplified in terms of earth thrust coefficients, unit weight, and wall height. An algorithm was developed to obtain earth thrust coefficients depending on various wall dimensions and internal friction angles and to prepare graphs representing earth thrust coefficients and failure surface angles. The effects of wall dimensions and internal friction angles on the earth thrusts and failure surface angles were determined. Finally, the proposed method of determining earth thrust coefficients was compared with other approaches.

This paper presents the derivation of a generalized nonlinear softening load-transfer model to analyze the load-settlement response for a single pile subjected to axial loading. The model requires the calculation of a single parameter, n, so that the number of field trial tests can be reduced significantly compared with other empirical solutions with multiple parameters. Variations in n can provide approximations for different soil–pile interaction systems. The model explicitly considers both the hardening and degradation behavior of skin friction with shear displacement. The effectiveness of the proposed method was verified through comparison of the evaluations with field measurements and other analysis results. A hyperbolic load-settlement model of pile-point resistance was incorporated with the load-transfer function for skin friction to develop an efficient computer program for settlement analysis of axially loaded piles. A comparison was made between the current approach and other analyses. Satisfactory performance was obtained for the new calculation framework, where the estimated settlement differed within 13%. In this paper, the softening effect of load-settlement response of a pile is also illustrated in a worked example.

The aim of this paper is to determine the influence of heating rate on the dynamic mechanical performance of coal measure rocks after heat treatment. Uniaxial compression tests were conducted using a split Hopkinson pressure bar system on coal measure rocks after heat treatment at 800°C at different heating rates. The results reveal that a high-temperature treatment changed the physical and mechanical properties of the sandstone. When the heating rate was increased, the natural and mechanical properties were reduced gradually. The failure mode of sandstone after heat treatment was tension destruction, and shear fracturing occurred locally only at high heating rates. Original cracks grew inside the sandstone after heat treatment, while the number of defects (including cracks and pores) increased gradually with an increased heating rate, which was the main reason for the change in the sandstone’s macromechanical properties. The energy dissipation during fracturing was correlated closely to the fracture characteristics and increased with increased heating rates. The results of this work can provide references for future engineering projects, such as underground coal gasification and coal-bed methane thermal exploitation.

In this study, the sloped ground subsidence of a jointed rock mass during tilted seam extraction was investigated using a trap-door model and discontinuous deformation analysis (DDA). In the trap-door model, the jointed rock mass was modeled by aluminum blocks. Sloped ground and inclined seams were produced by the rotary motion of the trap-door model around its center of rotation. The downward movement of the trap door simulated seam extraction, inducing subsidence of the sloped ground. A laser displacement sensor attached to the trap-door model during the extraction process recorded the ground settlement in digital data, which were used to plot subsidence profiles. Then, DDA was used to simulate the excavation process with the same geological conditions. The surface subsidence profiles in DDA were compared with those achieved with the trap-door model. Both experimental and computational results show that the change of the inclination angle affected the shape of the subsidence profiles. The surface subsidence profiles from the DDA simulation correlated well with those from the trap-door model. Thus, DDA is a potential method for predicting the sloped ground subsidence induced by mining extraction on inclined jointed rock strata.

In this study, the closed-form expressions of the incremental stresses (normal and shear) induced by a load moving at a constant speed in a rock medium containing free surface were obtained analytically. The closed-form expressions indicate that induced incremental normal (compressive and tensile) stresses vanish at the point directly below the point of application of shearing load on the boundary. Conversely, the value of incremental shear stress is maximal at this point. Thus, this comparative study aimed to analyze the influence of such parameters as irregularity depth, irregularity factor, heterogeneity parameter, types of heterogeneity, horizontal tensile initial stress, vertical compressive initial stress, and effective compressive initial stress on the incremental shear stress induced in three types of transversely isotropic rock media [sandstone (a sedimentary rock), granite (an igneous rock), and marble (a metamorphic rock)] for both exponential and linear heterogeneity. In this paper, the induced shear stress is computed numerically and demonstrated with the use of graphs to reveal the outcomes of the study. Furthermore, some considerable peculiarities are outlined and depicted graphically.

Three-dimensional (3D) failure criteria based on the Hoek–Brown (HB) criterion and a general Lode dependence for rocks were proposed in this paper. The proposed failure criteria inherited the compression meridian from the HB criterion and can include independent shear meridians to construct the failure envelop surface. Four failure criteria [Rubin-Willam-Warnke (RWW), Rubin-Pan-Hudson, R1.65, and Rubin λ (R)] with curved-triangular cross sections and two failure criteria with hexagonal cross sections (Rubin-Mohr-Coulomb and Rubin-Hoek-Brown) were shown as examples of applications of the general Lode dependence to demonstrate its versatility. The material parameters involved in the new failure criteria can be easily obtained from conventional triaxial compression (TXC) tests. Polyaxial compression (PXC) test data for six different rocks at a variety of stress states from published literatures were used to validate the proposed failure criteria, in which the best-fitting parameters obtained from the TXC tests were used to predict the rock failure in PXC states of stress. The comparison results demonstrated that three criteria (RWW, R1.65, and R) with similar cross section shapes gave better predictions than the other three criteria. One 3D failure criterion (R1.65) with an empirical factor (λ = 1.65) to define the independent shear meridian was considered to be the best among them because the RWW criterion tended to underestimate the strength for some rocks and the R criterion involved an extra parameter λ, which needed to be fitted from expensive PXC tests. The use of best-fitting parameters obtained from TXC tests can provide satisfactory predictions for rock failure with σ₂ dependence using the R1.65 criterion.

To investigate the wave (including P-wave and S-wave) propagation across a rock mass, the seismic discontinuous deformation analysis (DDA) method is used, and a time-frequency analysis of the DDA simulation results is performed in this paper. First, compared with the theoretical solution, the correctness of the DDA to simulate the seismic wave propagation across both the interlayer and interface is validated. Second, the propagation effects of the seismic wave across the jointed rock mass are studied, showing that the joint stiffness, joint spacing, and joint number have different effects on the attenuation of seismic waves. Last, to analyze seismic wave propagation across a rock mass, the engineering site of the underground cavern complex of the Dagangshan hydropower station in southwest China is used as a typical case study. A number of valuable results are obtained by time-frequency analysis; an obvious topographic amplification effect and a joint abnormal area are found. From the analysis of the time-space effect, it may be concluded that the relative displacement of the rock mass is easily encountered under earthquake, which adversely affects the stability of the engineering site. The spectrum characteristics of the seismic dynamic responses at different locations are significantly different, and a weak area of the peak acceleration may be caused by the joint attenuation effect. Based on the joint time-frequency analysis, it is suggested that adjustments for both the peak acceleration and spectrum be made before taking the ground motion record as the incident wave.

Traditional plasticity models of granular soils are usually established on different loading and plastic potential surfaces. This paper presents a nonassociated bounding-surface model by incorporating a fractional-order plastic-flow rule that is obtained by performing fractional-order derivatives on the bounding surface. It is found that the flow direction no longer necessarily coincides with the loading direction, even if the same potential and loading surfaces are used. The flexible ability of the model is then validated by simulating a series of experimental results of different granular soils, including ballast, rockfill, and sand, under both drained and undrained loading conditions. It is observed that the proposed model can well capture the key features (e.g., stress dilation, strain hardening/softening, and liquefaction) of various granular soils.

This paper proposes a novel optical fiber sensor-based nondestructive method, namely, the long-gauge fiber Bragg grating (LGFBG) method, for integrity assessment of cement-grouted soil nails. This LGFBG sensor was developed by encapsulating a number of straight, bare FBG sensors inside an aluminum tube, and then mounting them on a steel bar surface for monitoring average strain distributions of soil nails subjected to tension force. Measured strain distributions of LGFBG sensors were finally used for the prediction of effective elastic modulus (EEM) distributions along the soil nails and the assessment of soil nail integrity in terms of the predicted EEM. A number of pullout tests of soil nails with different defects in the laboratory were performed to verify the feasibility of this proposed method. Pullout test results indicate that the elongation contributions of defective soil nail sections are 1.5 to 3 times the intact soil nail sections, whereas the related EEM values of the two defective soil nail sections are around 0.3 to 0.5 times that of intact soil nail sections. The statistical hypothesis Student’s t-test was used to determine the magnitude ranges of the modulus ratio leading to a rejection of the null hypothesis for a prespecified level of significance. In this study, a significance level of 0.01% is suggested for the integrity evaluation of cement-grouted soil nails.

This paper suggests that the idea of the breaking strength of the brittle material scale being equal to the length scale was abandoned in the dynamic model brittle failure experiments. The concept of the failure load intensity scale, and that the breaking strength of the brittle material scale is equal to the failure load intensity scale, was put forward for the first time. This paper proposes an equivalent dynamic failure model test for a concrete dam subjected to strong underwater shock waves caused by explosions to illustrate the use of the similarity relationship. Based on the differential equation of motion for an elastic medium, similarity constraints on the time and Poisson’s ratio for elastic motion are obtained. Moreover, the constraints on the concrete’s strength and load are selected to simulate damage that is approximately the same. The equivalent test is based on drop-hammer equivalent impact models and empirical formulas that describe underwater explosions for four types of explosives, and the maximum pressure, impulse, elastic modulus, and strength of the model and prototype materials are similar. Finally, the numerical simulation is performed with a FEM to test with reliability the similarity relationship. By comparing the failure mode and pressure from the model test and numerical simulation, it can be considered that the experimental theory and method are partially validated. The similarity relationship proposed in the present paper provides more options for the selection of the material in the model. The proposed prediction method makes pollution-free, cost-effective, and easily operated simulations available.

This paper presents a novel unified solution to drained expansion of a spherical cavity in both clay and sand. The large-strain theory and a critical state model with a unified hardening parameter are used to describe the elastoplastic behavior of the soils after yielding. The elastoplastic constitutive tensor of the critical state model is developed to be a system of first-order differential equations for the drained expansion of a spherical cavity. The problem is formulated as an initial value problem in terms of the Lagrangian scheme by introducing an auxiliary variable and is solved numerically. With the present solution, curves for the expansion pressures, the distributions of stress components, and the stress paths are plotted to illustrate the different expansion responses in clay and sand. The proposed solution not only incorporates the dilatancy and peak strength of dense sand, but it can also reduce to the solution for clay and loose sand when ignoring the dilatancy and peak strength. Therefore, the present solution can be applied to interpret the cone penetration test and the pile installation, as well as to evaluate the pile end bearing capacity in various kinds of soils.

In the present study, extensive theoretical solutions in the form of charts have been generated based on a kinematically admissible translational mechanism for computing the passive resistance of cohesive-frictional soil retained by a rigid wall due to seismic body forces. With the application of the upper bound limit theorem of plasticity, the analysis was performed in the framework of a pseudostatic approach on an assumed composite collapse mechanism. This collapse mechanism comprises a radial shearing zone sandwiched between two triangular blocks, in which a new kinematically admissible velocity field is introduced, which provides upper bound values less than that computed by using the conventional logarithmic spiral and circular shearing zone reported in the earlier studies. The results are presented in terms of dimensionless passive earth-pressure coefficients due to the contribution of soil cohesion, surcharge, and unit weight of soil. The pseudostatic seismic forces do not affect the passive earth-pressure coefficients corresponding to the soil cohesion component; however, the passive earth-pressure coefficients, because of the soil unit weight and surcharge pressure, reduce considerably as the coefficients of seismic acceleration increase. Moreover, the reduction in passive earth-pressure coefficients is largely influenced by roughness, orientation of wall, slope angle of backfill soil, and the position of surcharge from the wall.

This study investigates the influence of soil–structure interaction (SSI) on period and damping of steel moment-resisting frame buildings supported by shallow footings on dry sand deposits. A series of impact hammer tests were conducted on a 3-story and a 6-story model steel frame for this purpose. Different base conditions (e.g., loose and dense sand beds, surface and embedded footings, heavily loaded and lightly loaded footings) were considered to gain a complete understanding of inertial SSI effects. Experimental results were compared with FEMA provisions as well as with analytical results obtained from a finite-element model. The period and damping amplifications are more prominent in the case of the 3-story building than in that of the 6-story building, indicating more sensitivity of short and stiff buildings to SSI over the taller ones. For a heavily loaded 3-story building on loose sand, the period and damping amplifications are 21 and 330%, respectively. Although the analytical results match well with those of the experiment, FEMA provisions tend to overestimate the responses, especially for the 6-story building.

To investigate the roof stability of deep cavities in layered soils, an axisymmetric failure mechanism based on the existing mechanism is proposed. Because deep cavities are generally under the water table, the adverse effects of pore pressure are taken into account. Limit analysis of the failure mechanism was conducted on the basis of the nonlinear power-law failure criterion, and upper-bound solutions of the failure curve were obtained. The procedure for the numerical calculation of the failure mechanism is proposed and the consistency of the failure mechanism is demonstrated. The roof failure involving two soil layers is discussed in detail to explain thoroughly the roof stability of deep cavities and tunnels in layered soils.

To exploit the resource of methane hydrate, it is crucial to understand the mechanical behavior of hydrate-bearing sediments. In this paper an elastoplastic constitutive model is developed for describing the mechanical behavior of gas hydrate–bearing soils (GHBS). To address the effect of the hydrate occurrence habits, the concept of the effective degree of saturation of the gas hydrate is introduced, and the effective stress stresses are redefined for describing the mechanical response of the GHBS. Within this context, a yield or loading function is developed while considering the bonding effect of gas hydrate; thus, the yield function can expand or shrink as gas hydrate forms or dissociates. To describe more realistically the mechanical behavior of the GHBS, a nonassociative flow rule is proposed by assuming the dilatancy to be a function of bonding stresses, suction stress, and stress ratio. The proposed model is applied to analyze the mechanical responses of the GHBS with different hydrate occurrence habits under different environmental loadings. It is demonstrated that the proposed model can well capture the main features of the mechanical behavior of GHBS, including the hydrate-induced enhancements of stiffness, strength and dilatancy, the unsaturation-related characteristics, and the hydrate occurrence habits dependency, showing that the proposed model is capable of describing the mechanical behavior of GHBS due to hydrate dissociation or under other environmental loadings.

This paper presents a numerical scheme for a solid–fluid coupled discrete-element method (DEM) that takes into consideration solid deformation and pore pressure generation and dissipation. Analytical solutions of conventional soil mechanics examples obtained by oedometer testing are used to quantitatively validate the proposed algorithm. The numerical results show good agreement with the analytical solutions. The proposed method advances the current capability of solid–fluid coupled DEM analysis to simulate the mechanical behavior of saturated granular materials.

With the development of column technology, a new concept of composite columns has been proposed. Composite columns integrate two columns into one single column, which has a small inner column installed in the middle of a large column. The purpose of the composite column is to combine favorable features of these two constituent columns. The inner and outer columns can have different stiffness, strength, and permeability values and different combinations. In this study, a sand–deep-mixed column was investigated, which included a deep-mixed (DM) column in the middle of a sand column. Because two component columns work together in the composite column, the load-transfer mechanism of the foundation becomes complicated. The bearing capacity of the soft foundation improved by composite columns has been studied. However, the consolidation of the soil foundation improved by composite columns has not been investigated. In this study, a finite-element method was used to model the soft foundation improved by the sand–DM composite (SDMC) column subjected to rigid loading. The SDMC column was fully penetrated through the soft soil and keyed into a firm soil layer. The concept of a unit cell was adopted, and one-quarter of the unit cell was utilized due to the symmetry of the model. The SDMC column was modeled as a linearly elastic perfectly plastic material, and the surrounding soil was modeled as an elastic material. Two additional soft foundations improved by sand columns and DM columns were modeled as well for comparison purposes. The stress concentration ratio, excess pore-water pressure, column bulging, and consolidation settlement of the three soft foundations were analyzed and are discussed. The numerical results show that the vertical effective stress on the top of the SDMC column increased to the maximum value and then decreased to the steady-state value, whereas the vertical effective stress on the top of the soil decreased first and then slightly increased to the steady-state value. The maximum stress values of the columns and the steady-state stress values of the soil indicated the yielding of the columns and the completion of consolidation, respectively. The process of stress transfer in the foundation improved by the SDMC column can be divided into the following three phases: (1) the stress was transferred from the soil to the inner DM column and the outer sand column before the inner DM column yielded, (2) the stress was transferred from the inner DM column to the outer sand column after the inner DM column yielded, and (3) the stress was transferred from the outer sand column to the soil after the outer sand column yielded. The SDMC column had a larger stress concentration ratio than the sand column but a smaller ratio than did the DM column. In addition, the SDMC column resulted in larger bulging and settlement than the DM column but smaller ones than the sand column. The foundations improved by the SDMC column and the sand column had higher degrees of consolidation than did the DM column.

Three-dimensional (3D) stability of a slope subjected to seepage forces is studied in this work in light of the kinematic approach of limit analysis. The widely used horn model for 3D stability of slopes is presented and discretized for the first time. To compute the seepage forces developed in a slope, 3D numerical calculations are used to solve the seepage-flow problem. The discretization makes it possible to calculate the seepage force acting on each element of the discretized horn mechanism by using the numerical results. The safety factors obtained by the proposed approach agree well with those given by numerical calculations. The influence of soil properties, 3D slope geometry, and anisotropic permeability is discussed in this work. Numerical results show that the 3D effect is important for B/H ratios lower than 10.0, beyond which the two-dimensional (2D) plane-strain analysis can be used for a 3D slope, and that a larger horizontal permeability with respect to the vertical one is a favorable factor for the slope stability.

This paper investigates deformation and stiffness anisotropy induced by damage propagation in a rock brittle deformation regime. Specifically, a finite-element–based Continuum damage mechanics model is used to capture sample size effects and the influence of intrinsic anisotropy on the stress–strain response of shale. The differential stress-induced damage (DSID) model previously proposed by the authors is calibrated against triaxial compression tests performed on North Dakota Bakken shale samples. Laboratory tests simulated with the FEM reproduce deformation and damage localization phenomena and capture the increase of boundary effects expected in larger samples. Simulations performed for various initial states of damage are used to investigate the role of the dominant fabric anisotropy of the rock: bedding planes in shale are modeled by a smeared damage zone with the DSID model and by a discrete crack plane. The continuum approach successfully captures the development of microcrack propagation and energy dissipation at the early stage of the strain hardening process observed in triaxial compression tests. Additionally, using initial anisotropic damage can effectively account for various types of mechanical anisotropy in shale.

The increase of rainfall and rise of groundwater level can cause frequent failures of unsaturated soil slopes that result in catastrophic landslides. This paper proposes a stochastic method for predicting the risk of failure of an infinite soil slope subjected to unsaturated infiltration flow. Stochastic models for shear stress and strength at an arbitrary plane of an infinite slope are developed. The accuracy of the proposed method is verified with the Monte Carlo simulation method. The merit of the proposed method lies in its analytical form, which can easily facilitate practical applications. Furthermore, a risk-based sensitivity analysis is undertaken in this study to identify the factors that are the most random and that affect the slope failure most significantly. It is found in this study that the developed stochastic models can capture the randomness of all factors that contribute to slope failure. It is also found that the slope inclination angle ($\theta$), soil air entry value (${\psi }_b$), water table rise from matric suction ($y_b$), dry soil unit weight (${\gamma }_d$), and soil-specific constant ($a_{\varphi }$) are important random variables in the accurate prediction of slope failure. The paper concludes that the proposed stochastic method can serve as a tool for geotechnical engineers to predict the risk of slope failure with accuracy and ease.

Generally, studies on structural design for bored tunnels focus on moderate to deep tunnels (cover-to-diameter ratio C/D ≥ 2). Such tunnel design methods cannot be used for shallow-situated bored tunnels because the influence of buoyancy is discounted, and actual loads on the tunnel lining are not taken into account properly. This paper proposes a new model that has more accurate loads on the tunnel lining combined with finite-element analysis for shallow tunnels. Internal forces and deformations of various shallow bored tunnels are investigated. The relationship between the optimal thickness-to-diameter ratio d/D of the tunnel cross section and the cover-to-diameter ratio C/D is also studied.

Sequestration of CO₂ in deep sedimentary reservoirs is one of the potential methods that can be used for reducing the level of CO₂ in the atmosphere. In this investigation, a geomechanical modeling study was performed for the deep Biyadh sandstone reservoir in Saudi Arabia. The results clearly demonstrate that the impermeable cap rock restricts the transport of CO₂ from the reservoir to the overburden layers. For a 10-year period of CO₂ injection, the simulation results show a ground surface upward displacement that spread over several kilometers around the injection site. It was also observed that the storage capacity of CO₂ increased exponentially as the injection pressure of CO₂ increased. The increase of the pore pressure with the passage of time, during CO₂ injection, altered the stress and displacement fields inside the reservoir. Moreover, the safe values of injection pressure for the reservoir were evaluated for the selected period of injection using Mohr-Coulomb failure criterion.

Principally, the interaction between chalk surface and saline water is vital for reported subsidence, formation compaction (the decline in pore fluid pressure within a solid structure and increase in stress on formation rock), and enhanced oil recovery (EOR) in chalk reservoirs. To understand the mechanisms of rock-fluid interaction and the role of specific ions in seawater, rock mechanical tests combined with chemical analysis of effluents were performed on chalk outcrops using synthetic brine solutions. All the chalk cores were treated with strictly aqueous solution, which means no hydrocarbon involved in any stage of experiments from preparation to postprocessing (chemical analysis). The two objectives in the present study are the examination of diffusion and transport-controlled phenomena in the presence of different aqueous chemistry and the proposal of possible processes/explanations based on distinct experimental scenarios. The experiments supply information on chemical mechanisms in chalk water weakening and the effect of saturation and flooding with the synthetic brine solutions, NaCl, Na₂SO₄, MgCl₂, CaCl₂, and synthetic seawater without magnesium (SSW-1[Mg²⁺]). Two different thermodynamic conditions (flooding state) were applied to the compacted cores within the creep phase: flooding steadily through the core and bypassing the core, both at high temperature and high pressure. The method provided measurements to investigate the effect of flow rate on the chemical reactions between the rock and fluid. Yield stress level, bulk modulus value, and creep strain rate are three mechanical properties of samples that were measured and analyzed together with chemical analysis of effluents taken periodically during the creep phase of each experiment. The results subsequently provided information about weakening/strengthening behavior within a time-dependent period. Switching of flooding fluid from distilled water (DW) to the NaCl solution tripled the creep strain rate and produced calcium content equal to seawater concentration. Performing a similar action on a DW to Na₂SO₄ solution generated enhanced creep of close to a factor of three. In addition, adsorption of sulfate to the chalk surface was identified. Flooding solely with NaCl solution or Na₂SO₄ solution caused a 25 and 50% decrease in chalk mechanical strength compared with DW flooded cores, respectively. MgCl₂ solution flooding experiments generated cores with 10% higher mechanical strength compared with cores treated with Na₂SO₄ solution. The observation was confirmed by testing cores with SSW-1[Mg²⁺] in which relatively low hydrostatic yield and enhanced creep strain were observed compared with Na₂SO₄ solution testing. Chalk cores flooded with MgCl₂ solution showed 25 and 50% lower mechanical strength values compared with cores tested with NaCl and DW. Collected samples from MgCl₂ and SSW-1[Mg²⁺] flooding showed simultaneous processes of magnesium retention inside chalk and production of calcium. Changing the flooding state to bypass with Na₂SO₄ solution did not generate any difference in the creep strain rate, whereas a change of flooding state from bypass to flooding triggered production of calcium equal to one-third of the calcium content in seawater. However, an opposite observation was recorded when the flooding state changed when using MgCl₂ as a flooding fluid. Change of the flooding state from flooding to bypass created enhanced compaction in the case of MgCl₂. The observed trend was similar when changing from bypass to flooding in the case of testing with Na₂SO₄ and SSW-1[Mg²⁺]. The extensive experiments provided a foundation for analyzing the behavior of chalk brine in the presence of oil and building verified models to simulate the effect of flooding complex brine and seawater on the mechanical characteristics of chalk and predicting the chemomechanical behavior of chalk.

This paper presents particle breakage and the drained shear behavior of sands. A series of drained shear tests were conducted on Silica Sand No. 5 and Coral Sand No. 3 under a 3-MPa confining pressure to produce the precrushed sands that were reused in triaxial tests to detect the influence of particle breakage. It was revealed that, for a given initial void ratio, particle breakage resulted in the impairment of the dilatancy of sands to become more contractive in influencing the shear behavior of the precrushed sands. Particle breakage resulted in the reduction of the peak-state friction angle and dilatancy angle, but the peak-state basic friction angle (the difference between peak-state friction angle and peak-state dilatancy angle) experienced first an increase and then a decrease with increasing particle breakage. For estimating the dilatancy angle by the excess friction angle (the difference between the peak-state friction angle and the critical-state friction angle), particle breakage was shown to have a significant influence on the friction-dilatancy behavior, including the accuracy of the excess friction angle to assess the peak-state dilatancy angle. The relations of the strengths and the void ratios of the precrushed sands were discussed as well. In addition, particle breakage resulted in a decrease of the critical-state void ratio but had a complex influence on the critical-state friction angle.

The freeway embankment linking Meizhou Island with Putian City in Fujian, China, passes through a shallow-sea area. Sand columns distributed in regular triangles and sand cushions reinforced with geogrids were employed to accelerate the consolidation of the soft ground beneath the embankment and improve its bearing capacity. In this study, three-dimensional (3D) finite-element analysis was carried out using the modified Cam-clay model to enhance the level of design and analysis of this complicated practical engineering problem of soft-ground improvement in terms of accurate prediction of the settlement, horizontal displacement, period of surcharge preloading, and variation of excess pore-water pressure. The predicted settlement and horizontal displacement of the embankment subgrade were found to agree well with the actual measurements. In line with the prediction of a consolidation degree of 95%, ultimately, the 340th day was determined to be the optimal date on which to remove the surcharge. In addition, the 3D effect of the variation of excess pore-water pressure was clearly revealed. The results prove that the 3D nonlinear numerical method presented in this paper is scientific and reliable for complicated practical engineering problems involving soft-ground improvement.

Blast-induced craters and ground vibrations caused by underground explosions are the foundation of explosion-resistance design for underground structures and protective facilities. In this study, large-scale blast experiments were performed in the field to investigate the characteristics of the ground vibrations and craters induced by single underground explosions in a loose, wet sand medium. Results from eight single blasts with emulsion explosives ranging from 200 to 400 g and buried depths ranging from 0.5 to 1.0 m are presented in this paper. A numerical simulation for Blast E8 using the coupled smoothed-particle hydrodynamics and finite-element method (SPH-FEM) is also presented. The influences of charge weight and buried depth on blast-induced crater formation and ejecta shape were studied. The experimental data for crater diameter were found to be roughly identical to the results suggested for wet sand. An empirical fitting formula for the ground vibration induced by single underground explosion in a loose, wet sand medium was developed using the vertical and radial components of peak particle velocity (PPV) obtained from the experiments. A numerical simulation using a coupled SPH-FEM was modeled to validate the experimental results and prove the method’s ability to model the blast-induced crater and ground vibration.

Conventional laboratory tests in geomechanics are inherently designed to create a uniform stress–strain field whereby relative homogeneity in data prevails at the expense of information diversity. The one-element convenience using stress homogeneity lends itself well to constitutive model calibration. From a mathematical standpoint, this approach potentially promotes uncertainty and error propagation. More recently, there has been a growing effort to utilize all data of conventional tests, including the effect of end restraints, to improve model calibration. This conceptual study revisits the notion of constitutive model calibration holding the perspective of inverse problems. For calibration purposes, nonconventional loading and complex boundary conditions were deemed to create a rich (nonuniform) strain–stress field. In this study, flexure excitation was investigated as a plausible test configuration in experimental geomechanics. An attempt was made to gauge the merits of flexural loading of a cylindrical soil specimen in providing independent data (information-rich test). The proposed test configuration was experimentally conducted and numerically optimized for assessment of model calibration.

All existing mathematical models for predicting deformation-dependent lateral earth pressure assume the at-rest state as the turning point for the relationship between lateral earth pressure and soil deformation. However, this assumption lacks rigorous consideration of the physical meaning of the turning point. In this study, the physical implications of the turning point in a general relationship between lateral earth pressure and soil deformation are analyzed. A simple hyperbolic model is subsequently developed and then validated using experimental results from plane strain loading tests. It is found that it is more appropriate to take the isotropic stress state as the turning point, because the principal stress orientation begins to rotate at this point. This finding is helpful and constructive for developing mathematical models that predict deformation-dependent lateral earth pressure. The proposed simple hyperbolic model can be used to describe well the measured nonlinear relationship between lateral earth pressure and soil deformation.

This paper presents an analytical and experimental investigation of Biot flow–induced damping in saturated soil specimens in resonant column tests. In the analytical investigation, the solid skeleton is treated as poroviscoelastic (i.e., equivalent linear). Biot flow–induced damping is evaluated based on the half-power bandwidth and free vibration decay methods. These solutions are found to be generally consistent with a closed-form analytical solution readily available in the literature. The solutions indicate that maximum values of Biot flow–induced damping occur in coarse sand and gravel, and can be practically neglected for less permeable soils (e.g., fine sand, silt, and clay). The solutions also indicate that Biot flow–induced damping increases as porosity increases, and decreases considerably as the ratio of the mass polar moment of inertia of the loading system to the specimen increases. In the experimental investigation, resonant column tests were conducted on granular specimens in dry and saturated conditions to quantify Biot flow–induced damping and compare with the analytical solutions. The test results are found to be in general agreement with the analytical solutions within the measurement accuracy of the device used in this study.

This paper presents an innovative semianalytical solution for the expansion of a drained spherical cavity with finite initial radius. The widely known modified Cam-clay model is adopted to capture the nonlinear elastoplastic behavior of soil. The rigorous definitions for the mean and deviator stresses are adopted. The problem is then formulated as a set of first-order ordinary differential equations in the Lagrangian form. The radial and tangential stress and specific volume distribution around the cavity are determined. Extensive parametric study is undertaken to investigate effects of the overconsolidation ratio and relative positioning of elastoplastic interface, among others. The applicability of the proposed theoretical approach is demonstrated by a comparison with laboratory test results.