International Journal of Geomechanics

Geomechanical properties such as shear strength, stiffness, and compressibility of soils subjected to subzero temperatures are of utmost importance for executing various projects related to infrastructure development and harnessing sustainable energy in cold regions. In this context, earlier researchers have employed sophisticated equipment such as triaxial equipment to establish these properties of the fine sands, which turns out to be quite expensive. To overcome this, a suitably modified low-cost temperature-controlled direct shear box apparatus has been fabricated. The setup’s utility and efficacy have been demonstrated by investigating the influence of the volumetric ice content, rate of shearing, and vertical stress on shear strength characteristics of the fine sands in their frozen state. In addition, the effect of (1) postfreezing shearing and the (2) confined-state freezing and shearing, the two methodologies that are generally adopted by earlier researchers on shear strength characteristics, have also been studied. Based on the extensive testing, it has been demonstrated that for frozen fine sands, the cohesion, secant modulus, and dilation angle increase with an increase in the rate of shearing and the volumetric ice content, and these variations can be expressed by power laws.

Developing data-driven predictive models is highly desirable for monitoring the condition of infrastructure assets but is dependent on the generation of large data sets that are regularly updated. This represents a challenge in modern geotechnical infrastructure projects such as earth embankments, where the size of settlement monitoring data sets is generally small and of low resolution. While long-term settlement predictions for embankment structures are useful for design engineers, short-term predictions are more valuable to site engineers who are required to make operational decisions regarding construction. Their challenge is greater on sites where ground conditions are complex. The purpose of this study is to explore the applicability of parametric data-driven methods (namely polynomial curve fitting and transfer function methods) to forecast the trend of soil settlement in real-time using magnetic extensometer and embankment fill-level data. An industrial data set was sourced for a highway earth embankment, which was founded on a sequence of interbedded glacial soils. Polynomials models were more effective in predicting settlement during earlier stages of embankment construction when information on the influence of loading on settlement is limited. As this information grows, transfer functions are preferable in terms of quality of prediction. The findings from this study highlight the potential for wider use of data-driven approaches to assist in earth embankment construction.

The arching phenomenon is intrinsic to granular materials and is a manifestation of the effects of their discrete microstructure. The fundamental mechanism of arching is the ability of discrete granular particles to transfer loads through force chains. Its effects are reflected through changes in the amount of stresses experienced by underground structures. Recent experiments and discrete element simulations have shown that stress distributions evolve, and different arching patterns form depending on the microstructure. While such studies can highlight the important effects of microstructures on soil arching, their use in developing solutions to arching in the field is limited. This study uses a double-slip gradient model implemented in the ABAQUS finite-element software to account for the microstructural effects and simulates the effects of arching in dry sand. The model assumes plastic deformation in granular materials to consist of dilatant shearing along two active planes. Furthermore, this model uses a gradient term of effective plastic strain that directly incorporates the effects of the material length scale. Numerical simulations were conducted to model the classic trap-door problem. It is found that strains begin to localize and form rupture bands during deformation. Furthermore, the pattern of localization of plastic strains is observed to be dependent on the orientation of the initial slip system. While arching effects were observed to initiate early with trap-door movement, its maximum effect is only realized after full localization. The variation of normalized vertical stress is found to be near linear and reaches a maximum value around a normalized height of 0.8 above the trap-door irrespective of the orientation of the initial slip system. On the other hand, the maximum value of the stress and the value of its reduction is dependent on both the displacement of the trap-door and the initial slip system orientation. It is shown that such a reduction in stresses cannot be predicted by the current analytical formulations, as they do not account for the effects of the microstructure or the amount of displacement.

To better understand the shear stress distribution in rock-cemented discontinuities, such as bedding planes and mineral-filled natural fractures (NFs), subjected to direct shear, an analytical solution for shear stress was first derived on the basis of the compression and bending theories of materials. The shear stresses obtained using the analytical solution for different conditions were then verified by the numerical simulation method. Finally, the main factors that influence the shear stress distribution in cemented discontinuities were explored using the analytical solution and numerical simulation methods. The results showed that the internal moment generated by shear forces significantly affects the shear stress distribution in a cemented NF. The analytical solution which considers the internal moment can accurately predict the shear stress distribution in most cases. The shear and normal stresses are both concentrated near the ends of cemented NF; however, they are comparatively uniform in the central portion. The shear stress concentration decreases with the increasing width of cemented NF, whereas it increases with Young’s modulus of cemented NF. The nonuniformity in shear stress decreases with the specimen height, and only when the specimen height is equal to the specimen length, the error produced by the analytical solution attains a minimum. The tractions on the loading surfaces are significantly nonuniform, and the nonuniform tractions are to balance the bending moment created by shear forces. Moreover, the shear box can dramatically influence the shear stress distribution in cemented NF. Uniform normal and shear displacements which represent the normal and shear forces loaded via a rigid shear box should be used for the boundary conditions. The findings in this study can provide a theoretical foundation for the evaluation of deformation properties and shear strength of intact rocks, rock interfaces, bedding planes, or mineral-filled NFs subjected to direct shear.

The mechanical behavior of basalt is critical to the stability and safety of large structures erected on basalt. In this paper, a series of tests (hydrostatic compression test, triaxial compression tests, and triaxial cyclic loading test) are conducted on basalt specimens from the Baihetan hydropower station in southwest China. The test results show that the crack closure (σ_cc), crack initiation (σ_ci), and crack damage (σ_cd) stresses are approximately 39%–43%, 54%–68%, and 74%–96% of the peak strength (σ_p), respectively. Based on the experimental results, a coupled elastoplastic damage model is proposed for basalt within a thermodynamic framework. In this model, elastic stiffness is affected by induced damage. Linear yield function and nonassociated flow rule are used to control inelastic dilatancy. Model parameters are determined from the triaxial compression tests and triaxial loading tests performed in this study. Comparison between numerical results and test results shows that the proposed model can accurately simulate the mechanical behavior of basalt under triaxial compression conditions.

Tunnel excavation by cyclic blasting caused accumulative damages to the surrounding rocks, reducing the intactness of the rock mass. The blasting impact contributes to the formation of an excavation damaged zone (EDZ) around the tunnel, which may induce disasters such as surrounding rock failure and roof collapse, hazarding the construction safety. This study, in view of Lame’s equation and Hoek–Brown’s failure criterion, deduced the equation of the strength reduction coefficient and established a method to calculate cyclic blasting disturbance factor D based on the wave velocity decrease rate. After modifying Hoek–Brown criterion parameters m_b and s based on the geological strength index, a method to calculate the thickness of the EDZ near the tunnel face was established, which quantified the EDZ range under the cyclic blasting disturbance. Subsequent theoretical calculations demonstrated a “three-stage” variation trend of the EDZ under cyclic blasting and revealed the EDZ thickness variation law with different excavation radii, initial stresses, rock strengths of surrounding rocks, disturbance factors, and lateral pressure coefficients.

This paper presents an analytical three-dimensional rotational mechanism for the limit analysis on the overall stability of slurry trenches in layered cohesive soils. The proposed mechanism differs from the traditional torus mechanism in terms of the assumption on the shapes of cross section. The proposed rotational mechanism can have cross section with arbitrary shapes that are described by a smooth rotation radius function. The factor of safety for the overall stability of slurry trenches is obtained by using the new kinematic mechanism. The performance of the proposed mechanism is evaluated by analyzing the overall stability of trenches in single-layered, uniform and nonuniform clayey soils. The computed results are compared with the solutions given by finite-element limit analysis (FELA), which show that the proposed mechanism can give better solutions than the traditional torus mechanism when the length-to-depth ratio of the trench is relatively small. Based on the proposed mechanism, the stability of slurry trenches in layered undrained clay is investigated. The results show that, for trenches in two-layered undrained clay, the strength ratio between the shallow and deep layers can significantly influence the depth of the collapse mechanism. For trenches in three-layered undrained clay with a weak interlayer, the thickness of the interlayer can greatly affect the modes of failure in terms of global or local instability.

This paper presents the numerical analysis of the lateral response of hollow circular caisson embedded in nonlinear soils. The caisson–soil system is modeled by a three-dimensional nonlinear finite-element method. The caisson is considered as a linear elastic body, whereas the nonlinear behavior of the adjoining soil is defined by kinematic hardening-based multiyield surface plasticity model. The interface between the caisson and adjoining soil is modeled by a zero thickness contact element which is defined by the constitutive relationships capable of describing the relative sliding and the separation at the interface. The present study discusses the lateral response of the hollow caisson, which consists of the lateral load versus lateral displacement (P–Y) curves, mechanism of deformation of the caisson–soil system, and deformation profile of the hollow caisson. It also presents the effect of the D/B ratio, relative stiffness of the caisson–soil system, and the effect of the vertical load on the lateral response of the hollow caisson embedded in nonlinear soils. The present study indicates that the D/B ratio, relative stiffness of the caisson–soil system, and the vertical load have a significant effect on the lateral response of the caisson–soil system. This study reveals that there occurs elastoplastic deformation during the lateral loading of the caisson–soil system. Further, a simplified transitional plasticity-based constitutive law is proposed to model the lateral response of a caisson–soil system. The proposed model requires only three parameters, which can be calibrated using the lateral load versus lateral displacement curve obtained from the finite-element analysis or the field test. Furthermore, mathematical relationships between the model parameters and the material parameters defining the caisson–soil system are established using the least-squares regression analysis.

Stability of underground working depends on geomechanical properties of rocks as well as geometrical and operational parameters of excavation. In this study, a fuzzy rule-based method, minimizing the subjectivity in rock engineering system (RES) is proposed to address the uncertainty in determining stability of underground pillars. A total of 243 elastoplastic 3D numerical models are analyzed by varying attributes of five input (leading) variables: (1) rock mass strength, (2) depth (in situ stress), (3) height of excavation (stope), (4) sequence of excavation with or without filling, and (5) crown pillar thickness. Interaction matrix between the leading input variables are evaluated using fuzzy “IF–THEN” rules considering the results of finite-element models (FEMs) and the “cause–effect” plot of the variables are also determined. Average equivalent plastic strain (EPS) over two consecutive pillars is the target output variable indicating the stability of the excavated zone (stope)–pillar system. Results of FEMs are plotted in the existing stope stability number graph and show that $\overline{\mathrm{ESP}}\approx 0.06-0.07$ denotes the boundary between “stable” and “transition” zone and $\overline{\mathrm{ESP}}\approx 0.09-0.1$ represents the boundary between “transition” and “caved” zone. A rib pillar stability index (RPSI) is formulated based on the vulnerability of a pillar for the evaluation of $\overline{\mathrm{EPS}}$ indicating the “stable” or “unstable” condition. Results show that plastic strain decreases exponentially with increasing RPSI having R² of 0.824. The proposed concept is applied to determine the stability of stopes of a hard rock mine by estimating RPSI and $\overline{\mathrm{EPS}}$ and finds that they are placed in “stable” zone for the given geomining conditions.

Fissured loess is one of the sources of geological hazards such as landslides and collapse under dynamic load. In this study, acrylic pipes with an inner diameter of 62 mm were processed into molds with different inclination angles (α = 0°, 15°, 30°, 45°, 60°, and 90°), and soil samples with preset fissure angles were prepared in two parts, i.e., loess block and weak interlayer. The sample was first vibrated by a test bench with sinusoidal waveform output, followed by uniaxial compression tests to investigate the mechanical properties of fissured loess before and after vibration. Results indicate that the failure mode of fissured loess is independent of the vibration disturbance; four types of failure modes were found after vibration, i.e., compressive fracture failure at α = 0° and 15°, slip failure at α = 60°, slip-fracture coupled failure at α = 45°, and compressive shear failure at α = 30° and 90°. The effect of vibration parameters on the stress–strain curve of fissured loess is mainly reflected in the decrease of both peak strength and initial elastic modulus. U-shaped changes of uniaxial compressive strength were observed in the ranges of 0°–45° and 45°–90°, respectively.

A novel approach––the modified multilayer method––is proposed for generating homogeneous specimens for discrete-element-method (DEM) studies. The “particle boundary” is introduced at the interface between the layers, and the general servocontrolled technique is extended to the particle boundary to apply the stress field. Each layer of the specimen is compacted by moving the top and bottom boundaries simultaneously to generate the desired DEM specimen. Unlike existing methods, the proposed approach generates highly homogeneous specimens. The mechanism underpinning the new approach was determined by investigating the effect of the boundary movement on the final spatial distribution of the particles. A comparison with experimental direct-shear results shows that homogeneous samples generated using the proposed approach can accurately model the deformation and strength of granular material, whereas other methods lead to deviations due to sample inhomogeneity.

Seismic performance of gravity dams has been widely concerned due to their importance in hydraulic engineering. In recent years, the influence of the incident angle of seismic waves and the inhomogeneity of complex foundation on the soil–structure interaction (SSI) system has become a focus. However, the foundation is often simplified to homogeneous elastomer when simulating nonuniform excitation seismic wave propagation due to the complex theoretical formulations. Therefore, this paper considers the stratification of foundation and analyzes the dynamic response of a gravity dam under obliquely incident seismic waves. First, the gravity dam–layered foundation interaction system is established in the finite-element software, and the concrete damage plasticity (CDP) model is adopted of the dam. Then, the displacements of the foundation under seismic P or SV waves with arbitrary incident angles are calculated by combining the one-dimensional time-domain method and the free wave field calculation method. Finally, adopting the wave input method based on the substructure of artificial boundaries, the seismic waves are converted to equivalent nodal forces on the viscous-spring boundaries of the layered foundation. Furthermore, the dynamic response of the dam on the homogeneous foundation is also simulated for comparison in this paper. The calculation results confirm that the impact of arbitrary incident angle of earthquakes and the parameters of foundation on the dam response is significant, and both should be considered comprehensively.

Invert anomaly has become a typical problem of railway tunnels in stratified rock during operations, which seriously affects the transportation capacity of railroad lines. This paper will study the failure mechanism and deformation behavior of an operational railway tunnel in horizontally stratified rock masses. Borehole investigations and in situ stress tests will be conducted to real the properties and stress state of the surrounding rock, and the characteristics of the structural distress will be detected via a structural inspection. A numerical analysis that considers the stratigraphic geological information and field structure state will be performed to study the structural stress and deformation response under different conditions of stratigraphic lateral pressure coefficient (K₀) and thickness of the stratified rock layer (L). The results demonstrate that the warping deformation of horizontally stratified rock masses below the tunnel invert was the main cause of the invert anomalies; however, when K₀ ≤ 1.0 or K₀ ≥ 2.0, and when L was in the range of thin-thick thickness to medium-thick thickness, there was a high risk of instability and cracking in the tunnel invert. In addition, the numerical analysis demonstrated that the rock reinforcement scheme could deweaken the layer effect of the rock masses and suppress the uplift deformation, which is recommended for practical projects.

This study presents an energy dissipation analysis approach for cavity expansion problems in crushable granular materials under the high stress state. By assuming that the energy dissipation generated from cavity expansion is mainly absorbed by the volume strain deformation in the plastic region, the energy conservation equations of the volume changes and energy dissipation in the plastic region during cavity expansion are reconstructed based on the compression failure mechanism. The limit pressure of the cavity expansion under high stresses is obtained based on a new critical state line for the crushable granular materials and the energy dissipation analysis method. The proposed approach is validated by the existed results. The effects of the initial void ratio and stress for the crushable granular materials on limiting expansion pressure of cavity expansion are investigated particularly. The results show that the effect is proved to be significant and must be considered in the analysis of cavity expansion problems, particularly for crushable granular materials at high stress.

It is important to assess the permeability characteristics of clays in the prediction of the postconstruction settlement of geotechnical projects on clay grounds. The coefficient of permeability in the vertical direction (k_v) and horizontal direction (k_h) of clays under different vertical effective stresses were measured using newly developed permeability test equipment to investigate the variations in the permeability and permeability anisotropy of reconstituted clays and their influential factors under one-dimensional (1D) compression. The evolution of the pore sizes and pore orientations was also investigated to clarify the corresponding micromechanisms. The test results showed that the permeability of the reconstituted clays was related to the mineral composition, clay content, void ratio, and clay fabric. The variations in k_v and k_h with the void ratio could be represented in terms of a linear e–log(k) relationship. Under the same strain, the values of k_h were obviously larger than those of k_v, and the permeability anisotropy ratio (k_h/k_v) values increased from 1 to 2 with increasing vertical strain. For all the tested reconstituted clays, both k_v and k_h generally decreased linearly with decreasing cumulative pore volume. For different clays with the same cumulative pore volume, k_v and k_h decreased with an increase in the plasticity index. In general, the anisotropy index of the pores increased, and the main orientation angle of the pores decreased with increasing vertical effective stress. For a certain clay, the increase in permeability anisotropy with vertical strain resulted from the gradual development of microstructural anisotropy. The findings of this study may assist in the accurate prediction of the consolidation behavior of reconstituted clays with vertical and horizontal drainage.

This paper develops an approach that utilizes kriging surrogate models for the reliability-based design of geotechnical structures. Surrogate models improve the computational efficiency and reduce the complexity of implementation to model the deterministic numerical models. This procedure involves the calibration of a kriging model, using samples generated by any deterministic geotechnical numerical model, which can be used in geotechnical design and optimization. Reliability-based design and optimization using a numerical model involve multiple calls of the numerical model, which is made possible with the kriging surrogate model. The procedure is illustrated through a simple shallow foundation example. The results demonstrate that reliability-based design and optimization based on surrogate modeling are efficient tools that can be used to design geotechnical structures.

The ram-compacted pile with bearing base (RBB) piling foundation has become one of the best solutions because it has low cost, high bearing capacity, and promising environmental benefits. However, its present design process relies heavily on some semiempirical calculations that typically lead to overconservative designs, meaning that costly pilot piling tests are commonly required before construction. This paper presents a novel finite-element modeling (FEM) cavity expansion method implemented in ABAQUS. First, the soil cavity limit pressure is obtained from FEM of a small spherical cavity that expands in a steady state, then the real horizontal diameter of the base is determined from the expansion modeling of a large cavity, and subsequently, the ultimate bearing capacity of RBB pile bearing bases is derived. The predictions obtained were validated by RBB pile static load test results from historic cases, showing that the FEM cavity expansion method is accurate and reliable. This study also explores the RBB piling mechanism from a cavity expansion point of view.

Durations are defined as an essential component of the three primary characteristics of strong earthquakes, which exhibit a remarkable influence on the damage characteristics of a concrete dam body. However, when considering the distinctive definitions of a strong motion duration, the influence of several durations on the seismic analysis of gravity dams remains unclear. In addition, there is no specific conclusion on the optimal choice for the duration of a strong ground motion. The endurance time analysis (ETA) method, which is a high-efficiency seismic performance method, is widely used, because of the high precision and low computation effort when calculating the dynamic responses of structures. However, when using this method it is almost impossible to account for any one type of duration contribution. Therefore, a modified ETA algorithm to correct duration effects will be proposed in this paper based on the three existing types of durations, such as bracketed (T_b), uniform (T_u), and significant (T_s) durations. The dynamic response will be further corrected using a modified ETA method in the numerical application to the Koyna concrete gravity dam, which is one of the largest dams in Maharashtra state, India. A group of 20 endurance time acceleration functions (ETAFs) and 10 sets of two-dimensional (2D) artificial waves with three total durations will be synthesized through the same site design acceleration spectrum. Three types of indices that include the dissipation energy, damage, and deformation indices will be used to measure the seismic performance. The nonlinear analysis results will be compared with those from the ETA and quantitative analysis methods, which show that the modified ETA method could provide an effective estimation to monitor earthquake resistance and structural seismic performance with a certain safety margin. The influence of the duration of a strong ground motion could be considered in the modified ETA method, which could be further applied in practical engineering.

The rock properties under periodic load are important to the stability of engineering works. It needs to analyze the mechanical properties and damage of deeply buried rock under periodic load. Taking granite in a mine as the research object, designed the experiment involving different cycles under different confining pressures and constant periodic upper and lower limit loads, carried out corresponding high-confining pressure cyclic loading experiment. The results show that a closed stress hysteresis loop is formed during loading and unloading cycles under different confining pressures. The hysteresis loop area of axial deformation decreases gradually with an increase of cycles. With the confining pressure increasing, the deformation modulus decreases gradually. However, under the same confining pressure, the deformation modulus remains almost unchanged as the number of loading–unloading cycles increase. As the number of cycles increase, the residual displacement shows an increasing trend whereas the axial and circumferential strains decrease. This can be explained by primary cracks gradually becoming compacted with the increase of cycles so that the proportion of axial elastic strain increases, the proportion of circumferential elastic strain increases. Fractal analysis of the T₂ spectrum shows that the sample has fractal characteristics before and after cyclic loading.

Split Hopkinson pressure bar (SHPB) tests have been used extensively to study the stress–strain behavior of sand under high strain-rate conditions. However, the low impedance of sand leads to specimens not attaining stress equilibrium; therefore, the reported results from SHPB tests, assuming stress equilibrium, might be invalid at low stresses. In this study, a model based on the discrete-element method (DEM) was developed to model SHPB tests on dry sand reported in the literature. The DEM model was calibrated and validated by comparing the simulated and reported stress–strain responses. The validated model was subsequently used to conduct a parametric study to investigate the effect of particle rotational resistance on the stress–strain response and stress equilibrium of the specimens. It was found that the DEM specimens did not attain strict stress equilibrium; however, the stress–strain responses obtained using the transmission bar stress (assuming stress equilibrium) and the average stress between the transmission and incident bars (assuming stress nonequilibrium) were within the error bar reported in the experiment. The parametric study showed that a higher particle rotational resistance resulted in a stiffer stress–strain response, and particle rotation meaningfully contributed to the sand response during SHPB tests.

Considering the hydraulic hysteresis caused by the change of contact angle at the soil–capillary water interface during the drying–wetting processes, this note proposes a novel hysteretic water-retention model. Compared with the previous studies, the model can take into account two distinct mechanisms, i.e., capillarity and adsorption, separately. The capillarity instead of adsorption is related to the contact angle hysteresis. Based on the Young–Laplace equation and the conjugate point on the main drying–wetting curve, the scanning equation is determined for the capillary part. It is evident that the new model is able to capture the hydraulic hysteresis behavior by comparing against experimental data from the published literature.