International Journal of Geomechanics

The mathematical structure of a constitutive model might be defined as the collection of variables that it contains and the symmetries, relationships, dependencies, and independencies that are involved. Finding a structure that is appropriate for modeling a particular set of behaviors is probably as important as finding the right formulae to use for the relationships within the structure. This study explored whether a structure similar to one used in steel frame plasticity might apply to soils. Ample evidence was found that it does, to a good approximation. Evidence included data of transversely isotropic linear elasticity, which appears to be exhibited by most soils and which can hamper accurate prediction of settlements or of dynamic responses using isotropic models. Evidence also included data on yield points and plastic flow. Both normality and deviations from normality were shown to be deducible as consequences of the operation of soil hinges. Hinges were shown to be consistent with the familiar concept of a state boundary that is different from a yield surface, and with critical and steady states.

According to the characteristics of the time-dependent dispersion coefficient of pollutant migration in soils, a one-dimensional pollutant migration model considering solute decay is established in the finite thickness soil. Based on the proposed model, the time-dependent boundary condition variable is considered, and different types of time-dependent dispersion coefficients are also assumed. The variable parameter k for pollutant diffusion time is used to control the time-dependent model. The analytical solution is obtained by separating the variable method. The results calculated by the presented analytical solution compared with those in the literature indicate solution accuracy and program reliability. According to the parameter study, variable k in the time-dependent model has a particular influence on the results, and the time-dependent and constant boundary conditions have a significant difference. The proposed method can be a reference for the landfill liner design.

The at-rest lateral earth pressure coefficient, which is called the k₀ coefficient, is an important parameter in geotechnical engineering. An accurate evaluation of k₀ is of great significance in both theoretic analyses and practical geotechnical applications. Existing analytical formulations for k₀ suffer one or more of the following limitations: (1) they have one or more unrealistic assumptions; (2) k₀ is derived as a constant for the very high stress state only, but implicitly applied to the entire stress range; and (3) the k₀ equation is often implicit and complicated, and it may require advanced mathematical and computational analysis. This paper provides a simple, explicit formulation to predict continuous changes of the at-rest earth pressure (k₀) coefficient as a function of stress for any critical state constitutive model for saturated soils without any assumption. The modified Cam-clay (MCC) model is used as an example to demonstrate the application of the proposed formulation. Procedures are developed to calibrate the model parameters for the MCC model using experimental results from the literature. The continuous changes of the k₀ coefficient are then computed during one-dimensional consolidation tests from which the effectiveness and simplicity of the proposed formulation are evaluated. Calculations indicate that a coefficient of determination around 99% is reached between the measured and predicted void ratios.

The effects of high temperature on rock strength and deformation, and hence the integrity of rock structure, have been a significant issue for rock mechanics and engineering. This article adopts a coupled thermomechanical (TM) solution method to explore the deterioration characteristics of heterogeneous rock under TM conditions. Based on the combination of damage mechanics and plasticity, a coupled material model with consideration of yielding, the plastic flow rule, damage evolution, the thermal effect, and heterogeneity was implemented in a commercial explicit finite-element code, LS-DYNA, through a user-defined material subroutine. Validation simulations indicate that the proposed model is capable of reproducing the mechanical behaviors of rock under unconfined compression and heating conditions. The effects of the heating temperature and homogeneity index on the mechanical properties were also investigated. The results indicate that rock exhibits prominent ductility characteristics with an increase in temperature regardless of the homogeneity index. With the same heterogeneity, monotonic reductions in unconfined compressive strength (UCS) and Young’s modulus and an increase in peak strain were observed with an increase in the temperature. A single oblique fracture dominated the failure of the rock with lower homogeneity, whereas two conjugate fractures developed in the rock with more homogeneous strength.

In this study, the coupled influence of contact time and rate of loading on the interface behavior of quartz grains was examined experimentally. The rate of loading is considered not just a tangential (or sliding) rate but a combination of both normal and tangential loading rates, which leads to the target normal load and tangential displacement for a given contact time. Two classes of tests were conducted; in the first class, steady-state sliding was first allowed to be reached by shearing the grains at a constant normal load before the application of the simultaneous normal load and tangential displacement variation, whereas in the second class, the normal load and tangential displacement were varied simultaneously from the start of the test. The experimental results from monotonic and cyclic micromechanical tests highlight the significant influence of the coupled load rate and contact time on the interparticle friction, tangential stiffness, and energy loss of the contacted interfaces. The results are compared with standard micromechanical experiments that were conducted under a constant normal load during the shearing of the grain contacts. Indirect qualitative analysis was performed to substantiate the increase in contact area with increasing contact time, which is not expected in constant normal load sliding.

In this study, we proposed an evolutionary complex variable method (ECVM) to find the analytical solution for the stress distribution in an infinite homogeneous, isotropic, and elastic rock mass. This ECVM was a combination of conformal mapping functions, firefly algorithm (FA), and the complex variable theory. Conformal mapping functions were determined by FA to transform arbitrary stope configurations into unit circles. The complex variable theory was then utilized to calculate two complex potential functions, resulting in stress distribution around arbitrary stope configurations solved. A case study involving the analytical solution around rectangular stopes was performed and validated by Abaqus finite-element software. The implementation of the proposed method for arbitrary stope configurations was discussed, and conformal mapping functions for several complex stope configurations were provided. The results showed that there was a good agreement between the analytical solution and numerical modeling. The difference between the analytical solution and Abaqus were mainly around stope corners, which might be because the grid size in Abaqus is not small enough. FA was found to be efficient and advantageous in the determination of conformal mapping functions. The proposed analytical solution has practical significance because it could be used for parameter sensitivity analysis, feasibility studies, and verification of numerical modeling.

In conventional discontinuous deformation analysis (DDA), the procedure called open–close iteration is adopted to enforce the contact condition, which needs to repeatedly fix and remove the artificial springs between blocks in contact to determine real contact states. The open–close iteration belongs to the category of trial-and-error methods, in which convergence cannot be always guaranteed. Meanwhile, the contact force is treated as concentrated force, leading to the difficulties in determining the shear strength from cohesion and stresses in the contact area. The so-called potential contact force concept adopted in the combined finite-element method and discrete-element method (FEM-DEM) has been proved efficient and robust. In the FEM-DEM the contact force is treated as a distributed contact force, which is more realistic and was utilized in this study to tackle contacts. A major advantage over the conventional DDA lies in the elimination of the need to handle singular contact types that would incur huge difficulties in three-dimensional simulations. Therefore, a contact potential–based DDA (CPDDA) was developed by introducing potential contact forces. Some typical examples, including those originally designed by the DDA inventor, are reanalyzed, proving the feasibility of CPDDA.

Starting from the thermodynamic framework of a mixture, combined with the modified soil-water characteristic curve (SWCC) model, and considering the granular-level energy dissipation caused by temperature and saturation changes, this paper presents a thermo-hydro-mechanical (THM)-coupled model for unsaturated clay soils. The THM-coupled model of unsaturated soils plays an important role in environmental geotechnical engineering. However, the physical basis of THM coupling problems has not been fully clarified. By extending granular solid hydrodynamics (GSH) theory to unsaturated soils, the constitutive relations of mean effective stress and plastic deformation can be quantitatively and theoretically determined. The model was validated by comparison with experimental data in terms of the influences of temperature and suction on compression characteristic, thermal volume change behavior, shear strength properties, and water-retention characteristics of the soil. As a result, the THM coupling behavior of unsaturated soils can be well interpreted.

Flowslides and retrogressive slope failures are usually triggered from a significant drop of shear strength in loose coarse-grained materials, including static liquefaction and successive large deformations. A 4-step procedure is proposed to model these phenomena using the material point method, together with an advanced constitutive model calibrated via inverse analysis. The numerical simulations are performed for a well-documented flume test, which showed that a flowslide was initiated by toe sliding followed by static liquefaction leading to retrogressive failure. First, an advanced hypoplastic constitutive model is calibrated to simulate the observed mechanical behavior of the representative elementary volume (REV) of soil in triaxial tests. Then, these model parameters are used to simulate the slope instability process observed in the flume test. The simulation of triaxial tests and slope instability are satisfactory and highlight important features about the evolution of pore-water pressure and effective stress in a large deformation slope process.

This paper investigates the structural and global stability of a cantilever-type retaining wall under seismic loading using numerical modelling. A new and robust approach is proposed to compute the seismic earth pressure behind the stem and along a virtual plane passing the heel of the wall. The results show that under different earthquake characteristics and wall geometries, the seismic earth pressure forces may be out of phase, leading to different seismic responses of the wall. The critical scenario for the structural stability is observed when the maximum acceleration is directed toward the backfill soil, and the earthquake frequency content is close to the natural frequency of the wall. In contrast, the critical scenario for the global stability occurs when the maximum acceleration is directed with minimum frequency content. Further, the natural frequency of the wall does not affect the global stability of the wall. However, the duration of the applied earthquake acceleration does affect the global stability of the wall, whereas the structural stability remains unaffected by it. In contrast with the current understanding, the possibility of failure of a cantilever-type retaining wall by horizontal sliding is remarkably increased with time of the applied earthquake acceleration.