查看更多>>摘要：Due to the significant physical property differences among various diagenetic minerals, it is crucial to characterize the multi-physics field evolution process of microwaves in heterogeneous rocks. To overcome the issues of insufficient refinement in existing numerical studies, this paper proposes a two-dimensional (2D) orthogonal model considering structural-material heterogeneous rocks for the detailed simulation of the strong coupling process of microwave radiation in rocks. Based on a high-fidelity granite model with texture structure, a strong coupled numerical simulation method is developed from both section and facade perspectives. Furthermore, the electrical-thermal-stress-damage physical responses of rocks to microwave radiation are meticulously calculated. The results indicate that both the section model and the facade model exhibit a stress distribution with central compression and surrounding tension, while the damage evolves from the inside out and from the surface inward, respectively. The change in the proportion of the tensile zone and the transformation of the stress properties of the mineral are the response characteristics of damage. The order of mineral damage is biotite, feldspar and quartz, with damage more likely to occur in the feldspar phase. Additionally, the texture structure and physical property differences in heterogeneous rocks are the main driving forces to rock damage. This study provides a novel simulation method for the microwave interaction with rocks and offers new insights into the evolution of multi-physics fields.
查看更多>>摘要：Integrating horizontal wells with multi-cluster fracturing techniques has effectively enhanced the contact area between hydraulic fractures (HFs) and the reservoir formation. However, field observations often reveal that fractures do not propagate uniformly, leading to resource wastage and potential interference between wells. This paper introduces a fully coupled XFEM model to investigate the influence of natural fractures (NFs) on the simultaneous propagation of multi-cluster fractures. By incorporating wellbore and perforation elements into the XFEM framework and reformulating pressure drop equations using Darcy's law, the model accurately represents fluid flow along both the wellbore and perforations. The XFEM approximates the displacement field, while the FEM handles the pressure field, with the resulting coupled equations solved using the Newton-Raphson iteration method. The validity and efficiency of the proposed model are demonstrated through comparisons with a four-fracture propagation problem. Sensitivity analysis indicates that NFs can disrupt uniform fracture propagation, with factors such as larger intersection angles, lower friction coefficients, and smaller NF apertures intensifying this effect. However, if the stress difference or intersection angle is relatively low, the impact of NFs may be temporary, allowing fluid partitioning to eventually become uniform. This study enhances the understanding of fracture propagation in the presence of NFs and provides valuable insights for optimizing hydraulic fracturing operations in fractured reservoirs.
查看更多>>摘要：An integrated constitutive model has been developed for rock-like materials, incorporating confinement-sensitive damage and bi-mechanism plasticity. The model aims to improve the capability of the conventional damage model in depicting the strengthening and brittle-to-ductile transitions that occur under both active and passive confinement conditions. A thermodynamic analysis of energy transformation and dissipation, considering both damage and plasticity, underpins the model's development. The model, rooted in damage-plastic theory, has been divided into two sub-models: (1) Confinement-Sensitive Model: This sub-model addresses the strengthening and ductility enhancements due to active confinement stress. It effectively captures the mechanical responses of rock-like materials under various levels of active confining stresses. (2) Endochronic Dilatancy Model: Based on endochronic theory, a separate dilatancy strain model is proposed, which effectively facilitates the interplay between lateral dilatancy and the growth of passive confining stress. Both sub-models, as well as the integrated model, have undergone validation using experimental data, including uniaxial tests, cyclic loading tests, actively confined tests, and passively confined tests of rock-like materials. These validations confirm the model's accuracy and reliability in predicting the mechanical behavior of rock-like materials under complex loading conditions.
查看更多>>摘要：Capturing dynamic water-soil variations and addressing water/soil boundary in numerical simulations of submarine landslide tsunamis remain major challenges. This study proposes a new two-phase two-layer Riemannsmoothed particle hydrodynamics (SPH) numerical model. In this model, the soil satisfies the Drucker-Prager yield criterion and water is treated as a weakly-compressible fluid. The SPH method based on a low-dissipation Riemann solver, is innovatively introduced into the mathematical framework of water-soil coupling to simulate the dynamic behaviors of two overlapping water and soil particle layers. The no-slip boundary treatment based on a one-sided Riemann format is proposed to achieve the water/soil-solid coupling in landslide simulations. The volume fraction is fully participated in the current SPH discretization process, and the Riemann solver is also applied to improve its calculation. Validations against two static and dynamic water-soil coupling cases demonstrate that present approach is effective. Then, the proposed model with different particle resolutions is further applied to explore the submarine landslide tsunamis under two different configurations. The landslide motions exhibit good agreement and convergence with experimental data, and dynamic water-soil evolutions during the landslide process are properly captured with reasonable dissipation control, which indicates the accuracy and usability of the current Riemann-based two-layer model.
查看更多>>摘要：Enzyme induced carbonate precipitation (EICP) is an effective and promising biocementation technique for soil reinforcement. Calcareous sands exhibit special physical characteristics, including complex particle shapes, angularity, and abundant inner pores, due to their unique biogenesis. The mechanical behaviour of EICP-treated calcareous sands could be influenced by both the cementation level and particle breakage. In this study, triaxial and one-dimensional compression tests were conducted on untreated and EICP-treated calcareous sands with varying cementation levels. Results show that the strength and dilatancy were significantly improved by increasing the carbonate content, resulting in more obvious brittleness in the EICP-treated calcareous sands. Both the bond strength and the yield stress followed exponential relationships with the carbonate content. By introducing bond strength and particle breakage yield stress, a constitutive model was developed within the framework of super-subloading concept. Relationships between the state variables and carbonate content were quantitatively addressed. The simulation results agreed well with the experimental measurements, demonstrating the effectiveness and capability of the proposed model to describe the mechanical features of the calcareous sands treated under various cementation and stress conditions.
查看更多>>摘要：Contact detection and contact geometry are among the most important steps in Discrete Element Method (DEM) simulations. Accurately representing the contact between two particles is crucial, and when modeling fractured rock using polyhedral particles, the accuracy of the contact point calculation is essential for obtaining realistic and reliable simulation results. The point of contact is where contact forces are applied to particles in a DEM simulation and, thus, an inaccurate representation of that point leads to artificial torque acting on particles, resulting in non-physical rotation and particle interactions. Herein we present a new algorithm for accurately calculating the contact point between two colliding polyhedral particles. The algorithm uses the topology of the particles to assert their interaction with the plane of contact and not directly with each other. The new algorithm provides improved performance in terms of global stability of DEM models by mitigating numerically induced instability associated with errors and sporadic movement in the contact point calculation. The performance of the new algorithm is showcased in several examples that illustrate how accurately representing the contact point is a requirement for generating reliable numerical simulations.
查看更多>>摘要：Geotechnical hazards usually involve interactions between different materials or phases such as water-structure interaction, water-rock interaction, soil-structure interaction, or soil-rock interaction. Accurate and efficient simulation of such phenomenon can be challengeable due to the complex interactive mechanism and large deformation. A newly coupled DualSPHysics (an open-source Smoothed Particle Hydrodynamics solver platform) - Discontinuous Deformation Analysis (DSPH-DDA) technique is developed by combination of two- and threedimensional DDA and DualSPHysics. DDA is executed in CPU with independent time step size, and a synchronizing technique is developed to maintain the pace between two systems. Besides, for describing soil behavior, an elastic-plastic soil constitutive model is also incorporated into DualSPHysics. The spring-dashpot contact model is adopted to idealize particle-block interactions. Five numerical examples are conducted to demonstrate the performance of the newly coupled DSPH-DDA technique, including the soil column collapse, the free surface flow impacting on an elastic structure, the dam break flow impacting on cubes, modular-block soil retaining wall collapse, and the tunnel face collapse with varied rock contents of soil-rock-mixture model ground. The simulation results are consistent with the experimental data. Conclusively, this newly coupled DSPH-DDA technique is applicable to describe large deformation and failure behavior of coupling problems in geotechnical hazards with high accuracy and calculation efficiency.
查看更多>>摘要：Electroosmosis is a dewatering technique for fine-grained soils that, by means of an electric current passing through a series of electrodes, moves a volume of pore water from the anodes toward the cathodes. The dewatering process can effectively reduce the soil water content but often results in the formation of surface cracks. The cracks collectively reduce the passage of the electric current, thereby diminishing the dewatering efficiency. To optimize dewatering, crack formation must be studied. A numerical model to predict soil cracks formed during the electroosmosis dewatering process is developed in this paper. This model considers the unsaturated conditions during dewatering and combines the constitutive surface of unsaturated soils with the Mohr-Coulomb failure envelope to determine cracking. This model also accounts for the nonlinear variations in soil properties, the degree of saturation, and cracking. This model is validated against laboratory test results and is applied to various example problems. The research outcomes result in the assessment of crack evolution and the identification of factors that affect crack development.
查看更多>>摘要：The stress state and density of soil have been considered as the key factors to determine the liquefaction resistance. However, the results of seismic liquefaction case histories, laboratory tests and centrifuge model tests show that the fabric characteristics also influence liquefaction resistance, even more significantly than the contributions of stress state and density. In this study, anisotropic specimens with different consolidation histories were prepared using the 3D Discrete Element Method (DEM) to investigate the influence of fabric characteristics on the mechanical behavior of granular materials and the underlying mechanisms. The simulations revealed that under monotonic shear conditions, horizontally anisotropic specimens exhibited strain hardening and dilatancy characteristics, as well as higher peak strength. Under cyclic shear condition, the normalized liquefaction resistance of the specimens showed a strong linear relationship with the degree of anisotropy, independent of confining pressures and density. Microscopic results indicate that the fabric arrangement aligned with the loading direction leads to the evolution of the mechanical coordination number and average contact force in a manner favorable to resisting loads, which is the underlying mechanism influencing macroscopic mechanical properties. Additionally, the evolution patterns of contact normal magnitude and angle in anisotropic granular materials under cyclic loading conditions were also analyzed. The results of this study provided a new perspective on the macroscopic mechanical properties and the evolution of the microstructure of granular soils under anisotropic conditions.
Wu, XiaotianYao, YangpingDong, LiangPotts, David M....
1.1-1.13页
查看更多>>摘要：When the conventional finite element (FE) method is used in the simulation of strain-softening soils and the accompanying appearance of shear bands, the predicted results can exhibit a significant mesh dependency and may suffer from convergence difficulties. Nonlocal strain regularisation has been shown as one of the reliable approaches for overcoming such problems. This paper first demonstrates how a modified substepping stress point algorithm, that incorporates the nonlocal strain regularisation, can be developed for constitutive models which have multiple state variables in their hardening/softening rule. The algorithm is derived for the unified hardening (UH) model as an example of such models, which was developed to account for the constitutive characteristics of both clays and sands. The capability of the nonlocal UH model is then verified through analyses of boundary value problems involving dense sands, demonstrating a very good performance in eliminating the problem of mesh dependency while maintaining a stable solution process. Recommendations are also provided on how to determine the values of nonlocal parameters for the analysis of full-scale engineering problems using the proposed nonlocal algorithm.
NETL
NSTL
Elsevier