AbstractThis paper presents a 3D spectral numerical scheme that can accurately model planarcracks of any shape residing on an interfacial plane between two elastic solids. The cracks propagate dynamically under the action of interfacial loads and interfacial constitutive laws. The scheme is a spectral form of the boundary integral equations (BIE) that relate the displacement discontinuity fields along the interfacial plane to the stress fields at the plane. In the BIE, the displacement discontinuities are expressed as a spatio‐temporal convolution of the traction components at the interface. This is in contrast with most previous studies which use a spatio‐temporal convolution of the displacement discontinuities or of the displacements at the interface. Due to the continuity of tractions across the interface, the present formulation is simpler, resulting in convolution kernels that can be written in closed‐form. Previous studies have relied on numerically obtained convolution kernels. The accuracy of the proposed scheme is validated with the known analytical solution of the 3D Lamb problem. Furthermore, new algorithms are developed for coupling the BIE with a slip‐weakening friction law, both for homogeneous materials as well as for bi‐material interfaces. This results in a widely applicable formulation for studying spontaneous rupture propagation. The algorithms are validated by comparing rupture simulation exercises to benchmark problems from Southern California Earthquake Center (SCEC). Finally, the methodology is used to simulate 3D frictional rupture propagation along a bi‐material interface.

AbstractFluid injection‐induced deformation around a cylindrical cavity is of particular interest in the area of subsurface energy extraction. In this study, a model is proposed to analyze the time‐dependent expansion of a cavity caused by fluid injection in an elastoplastic dry porous medium. This problem is characterized by the existence of two moving boundaries, a permeation front and an elastoplastic interface, which leads to distinct time‐dependent zones governed by different sets of equations. The interplay between these two boundaries leads to three phases of solution. The a priori unknown partitioning of the injection rate into the rate of change of cavity volume and infiltration in the porous medium necessitates the introduction of a time‐dependent permeation coefficient as one of the primary variables. The method of solution takes advantage of the quasi‐static and quasi‐stationary nature of the problem, which makes it possible to treat time as a parameter rather than a variable. It follows that the problem can be solved in two steps. In a first step, closed‐form expressions for the pore pressure, displacement, and stress fields in each zone are derived, with parameters in these expressions depending explicitly on four time‐dependent variables, namely the positions of the two interfaces, the cavity radius, and the permeation coefficient. In a second step, the rate equations governing the evolution of these variables during different phases are derived and solved numerically. The paper concludes with a parametric analysis of the influence of the stiffness and strength of the material on the solution.

AbstractThis paper presents a numerical study of the effects of the particle's shape and its interaction with surrounding fluid on the mechanism of sandpiles formation in air and water, respectively. This study is motivated by the fact that seabed sediments are predominantly deposited in water and consist of non‐spherical particles. In our study, a non‐linear contact model is employed in the Discrete Element Method. At the same time, the void fraction model and drag force model of non‐spherical particles with sharp corners are further improved. Based on the above two advancements, an extended computational fluid dynamics‐discrete element method (CFD‐DEM) approach coupled with the super‐quadric model is developed. It can accurately simulate multi‐collision and interlocking characteristics between non‐spherical particles, as well as particle‐fluid interactions. Subsequently, the validation and applicability of this extended CFD‐DEM approach are proved by comparing the results of experiment and theory models for various cases. The discrepancies induced by particle shape are revealed in terms of repose angles, porosity, and stress distribution. This is due to non‐spherical particles exhibiting a significant occlusal interlocking effect, which enhances inter‐particle friction. Additionally, the influence of ambient water is non‐negligible, as it supports a portion of the upward particle weight during the process of sandpiles formation. The above findings can be substantiated by analyzing the fabric structure of sandpiles. Such coupling of macro‐ with micro‐scale insights into the fundamental geomechanical issues will further extend to wide fields, particularly sea‐water‐flow‐induced seabed instability.

AbstractThe elastic viscoplastic properties are non‐negligible factors of clays that cause the deviation between the theoretical and the measured values, which were rarely incorporated in layered consolidation problems. Thus, this paper extended a generalized bi‐layered one‐dimensional (1D) consolidation model for soft ground under ramp load, simultaneously incorporating elastic viscoplastic deformation, non‐Darcy flow (NDF), and time‐dependent drainage boundary (TDB) condition. The finite volume technique was employed to numerically solve the control equation. Then, the proposed method solutions were verified by comparing with degenerated cases, including oedometer experimental results, analytical and semi‐analytical solutions with different boundary conditions. Furthermore, parametric studies were conducted on the bi‐layered clay creep consolidation characteristics by investigating the effect of the loading rate, interface and flow parameters, and the relative soil layer properties. The results demonstrate that the entire dissipation rate of the excess pore‐water pressure (EPWP) and settlement rate in the bi‐layered ground become faster as the soil thickness with high permeability or low compressibility increases. When considering the viscosity of soft clay, the EPWP exceeding the overlying construction load value can occur in poorly drained locations. Neglecting loading rate, time‐dependent drainage boundary (TDB), and NDF can result in a significant overestimation of consolidation and settlement proceedings.

AbstractDynamic wave reflections would interfere with the laboratory observation of the soil arching under cyclic loading when a traditional trapdoor model with rigid boundaries was used. This problem would be prominent when investigating the soil arching in pile‐supported embankments where the stationary support (pile) would be small, making the rigid boundary close to the domain of interest affected by dynamic loads. To avoid dynamic wave reflections and narrow the calculation domain, soil arching within a pile‐supported embankment under cyclic loading is numerically investigated in a multi‐span segmented trapdoor model with flexible boundaries by the particle flow code (PFC). In addition, a pavement structure is included and the springs supporting the trapdoor follow a bi‐linear constitutive model. The energy‐absorbing flexible boundary at the bottom weakens the dynamic wave reflections and is in favor of passing vertical dynamic waves to compact the fill and weaken the influence of cyclic loading on the soil arching effect during the loading stage. Lateral flexible boundaries would facilitate realistically reproducing the effect of cyclic loading on the soil arching because they could consider the weakening of the plugging effect that occurs during the lateral expansion. The development of soil arches of mid‐span and side‐span are different when the load applied at the mid‐span is laterally transferred to adjacent spans by the arching effect.

AbstractFrost heave can lead to both the ground uplifting and frost heave pressure under different circumstances, and cause many engineering problems. To describe the characteristics of frost heave under various thermo‐hydro‐mechanical (THM) coupling conditions and calculate both the frost heave amount and the frost heave pressure, the coupled THM process, as well as the phase change of the pore water, should be considered for freezing soil. In this paper, thermodynamic equilibrium conditions in saturated freezing soil were derived to account for the mechanical effect on the cryogenic suction and unfrozen saturation of pore water during phase transition. Then the governing equations were developed considering the water flow, heat transfer, stress equilibrium, phase change, ice segregation, and their complex interactions. Based on that, a numerical model considering fully THM coupling is presented within the framework of finite element provided by COMSOL. Both frost heave amount tests and frost heave pressure tests were simulated to verify the proposed model. Then the model was applied to subgrades with different types of soil and different boundary conditions, to reveal the characteristics of frost heave amount and frost heave pressure under different conditions, and at the same time to demonstrate the model's applicative prospect.

AbstractBituminized waste products (BWPs) were produced by conditioning in bitumen the co‐precipitation sludge resulting from industrial reprocessing of spent nuclear fuel. Underground geological disposal is a solution for the long‐term disposal of some intermediate level long‐lived (ILW‐LL) categorized BWPs in France. After one or several hundred thousand years, the water from the host rock will fully saturate the disposal cells. By an osmotic phenomenon enabled by the semi‐permeable capacity of the bituminous matrix, water in direct contact with BWPs could cause them to swell, which would lead to pressure on the host rock and may damage the disposal facility. Therefore, the BWPs’ swelling behavior has to be taken into account in safety studies for disposal facilities. This paper presents an experimental and numerical investigation of BWPs’ swelling behavior due to water uptake. Experimentally, water uptake, swelling and released salts were monitored for about 4 years during free leaching tests of simplified BWPs. The numerical model presented is extended from an existing one that incorporates transport mechanisms (diffusion, permeation, osmosis) with mechanics via Maxwell's viscoelastic model. An original coupled homogenization of transport terms is proposed to better capture the role of the semi‐permeable membrane played by the bitumen and the porosity dependency of coupled transport coefficients during water uptake. The presented numerical model is able to reproduce the experimental results of free leaching tests and shows its validity for the entire leaching process.

AbstractStrainburst often occurs in the loading process of tangential stress concentration from surrounding rocks after excavation and unloading of deep rock mass. The concentrated tangential stress is relatively larger on the tunnel walls, which decreases towards the interior of surrounding rocks with a certain gradient. To explore the fracture evolution characteristics of surrounding rocks under different tangential gradient stresses and understand various phenomena in the strainburst process, a large‐scale true‐triaxial gradient and hydraulic‐pneumatic composite loading rockburst test device was adopted to carry out the strainburst tests under four different gradient stresses. Based on the macroscopic failure phenomena, distribution of rockburst debris, macro‐micro morphology of failure cross section, and monitored data of acoustic emission (AE), the fracture evolution of rockburst specimens was analyzed under different stress gradient loadings. The results indicate that the stress gradient has an obvious influence on the fracture characteristics, resulting in different rockburst phenomena. With the increase of stress gradient, the failure stress of rockburst decreases, while the dynamic failure characteristics of rockburst trends to be significant. The increase of stress gradient contributes to higher fragmentation degree of debris, more uniform distribution and better continuity. The total number of cracks in the model decreases with the rise of the stress gradient, and the proportion of shear failure increases, which is the main reason for the enhancement of the rockburst intensity.