International Journal for Numerical and Analytical Methods in Geomechanics最新文献

The dynamic pile-soil interaction significantly affects the accuracy of pile vibration response analysis. However, currently, there is no well-established method for simulating pile toe soil under high-strain dynamic loading (HSDL), which presents a major challenge for pile driving analysis. This paper proposes a fictitious soil pile model to simulate reactions and stress wave propagation in the base soil under HSDL. The pile toe soil was regarded as a fictitious soil pile extending downward to the bedrock at a certain cone angle, considering the non-linear soil stiffness, radiation damping, and hysteretic damping. The solution of the soil responses was given by differential iterative method combined with MTLAB programming. The model's accuracy was validated against a three-dimensional (3D) finite element model and the Smith model. Sensitivity analysis was performed on parameters such as discreteness, time interval, cone angle, and non-linear stiffness. The model shows advantages in simulating stress wave propagation in pile toe soil under HSDL, with attenuation rates decreasing with depth and wave speeds stabilizing after an initial decrease. The soil elastic modulus, pile diameter, cone angle, and impact loads influence the attenuation rate, while only the elastic modulus significantly affects wave speed. The results could be helpful for the simulation of the pile toe soil under HSDL and the study of the attenuation of stress waves in the soil.

The numerical investigation in this study focuses on the propagation of hydraulically driven fractures in deformable porous media containing two fluid phases. The fully coupled hydro-mechanical governing equations are discretized and solved using the extended element-free Galerkin method. The wetting fluid is injected into the initial crack. The pores are filled with both wetting and non-wetting fluid phases. Essential boundary conditions are enforced using the penalty method. To model the discontinuities in field variables, the extrinsic enrichment strategy is employed. Ridge and Heaviside enrichment functions are utilized to introduce weak and strong discontinuities, respectively. The nonlinear behavior in front of the crack tip is defined by means of a cohesive crack model. Continuity equations for wetting and non-wetting fluids through the fracture domain are expressed using Darcy's law and cubic law. The coupling terms of fluids are considered in accordance with their mass transfer among the crack and the surrounding domain, simulating the fluid leak-off phenomenon and the fluid lag zone. The results demonstrate the success of the proposed numerical framework in simulating the intricate aspects of the hydraulic fracturing process. Sensitivity analysis is performed with varying domain permeabilities and wetting fluid viscosities to elucidate their effects on different aspects of hydraulic fracture.

During the process of treating soft soil foundations with prefabricated drainage drains (PVD), “soil columns” form around the PVD, and a “weak zone” forms outside the range of the “soil columns.” The difference in properties between the two forms a distinct interface, leading to a gradual decrease in drainage efficiency and obstruction of vertical drainage channels, which in turn causes cracks and lateral displacement in the soil during consolidation. The interfaces between adjacent soil layers are incomplete contact, and the water within the interstices impedes the transfer of heat, manifesting a thermal resistance effect. To address this phenomenon, a synchronous measurement system for the thermal gradient and the heat flux density between the soil interfaces has been developed. Applying Fourier's law of heat conduction, the thermal resistance coefficient has been determined. Based on the theory of thermo-hydro-mechanical coupling, a multi-zone axisymmetric model for saturated soils that considers thermal resistance effect has been proposed. Semi-analytical solutions were derived and validated through comparison with the custom FEM model and field experiments. The thermal consolidation characteristics of the multi-zone soils under various thermal contact models have also been discussed, with a comprehensive analysis of the influence of different parameters. Outcomes show that: the generalized incomplete thermal contact model provides a better description of the thermal resistance phenomenon between multi-zone soils interfaces; ignoring the thermal resistance effect leads to an overestimation of the deformation during the thermal consolidation, and, the thermal resistance effect decreases the influence of the thermo-osmosis effect on the consolidation characteristics.

Soil–rock mixture (SRM) slopes consist of soils and rocks and are widely distributed globally. In addition to heterogeneity and discontinuity within SRM slopes, the inherent spatial variability can be observed in soil and rock properties. However, spatial variability in rock and soil properties and layouts has not been well considered in the stability analysis of SRM slopes. Additionally, SRM slopes commonly show a rotated anisotropic fabric pattern, while such fabric has rarely been accounted for in SRM slope stability analysis. In this study, a two-phase rotated anisotropy random field simulation method is proposed to model these spatial variations simultaneously. The proposed approach is then integrated with the finite element method (FEM) to study the impacts of soil volume fraction and bedding dip angle (i.e., rotated anisotropy) on the probability of failure (p_f) and failure mode of SRM slopes. It is found that considering only spatially varying layouts can underestimate p_f by up to 97% compared to considering both spatially variable properties and layouts. The increase in soil volume fraction significantly improves p_f and the likelihood of deep failure. The bedding dip angle greatly influences p_f, yet deep failure remains dominant across different bedding dip angles. Furthermore, the failure mode of SRM slopes is more sensitive to the changes in soil volume fraction than to bedding dip angle.

Static liquefaction-induced failure in tailings dams can result in extensive economic and environmental damage. In practice, the use of constitutive models capable of capturing this phenomenon and assessing structures susceptible to liquefaction is increasing. Numerous constitutive models exist and have been applied to model static liquefaction of tailings materials, but the extent of the influence exerted by the choice of constitutive model on analysis outcomes remains to be determined. This study addresses this uncertainty by employing the Clay and Sand Model (CASM) and NorSand models to analyze the well-documented case of the B1 dam failure in Brazil. Initially, a back analysis of the failure was conducted, and further analyses were carried out by simulating hypothetical triggers: crest loading and increased gravity. The influence of the adopted constitutive model on results was analyzed through the failure mechanisms generated, stress paths, and levels of disturbances necessary to trigger liquefaction. Both models produced compatible failure mechanisms, with slight differences observed in the level of disturbance required to trigger liquefaction. The results obtained from the B1 case indicate that the most important aspect related to the constitutive model in assessing structures susceptible to static liquefaction lies in the constitutive model's capacity to represent the sudden strength loss due to pore pressure generation, while the particular formulations employed in each method tend to be a secondary consideration in the analysis.

Permeable pipe pile, a novel pile foundation integrating drainage and bearing functions, improves the bearing capacity of the pile foundation by accelerating the consolidation of the soil around the pile. In this study, a mathematical model is established to simulate the consolidation of surrounding clayey soils and the pile–soil interaction, where the rheological properties of the soils are described with the fractional derivative-based Merchant model, and the impeded drainage boundary is used to simulate the pile–soil interfacial drainage boundary. Corresponding solutions for pile–soil relative displacement, skin friction, and axial force on the pile shaft are derived by means of semi-analytical methods, and they are validated by comparing with experimental results and numerical simulation results. Based on the proposed semi-analytical model, a series of parametric analyses are conducted to investigate the influences of fractional orders, viscosity coefficients, pile–soil interface parameters, and pile-head loads on the pile–soil interaction characteristics. It is observed that during the transition stage, the axial force increases linearly with depth in the plastic segment, and then increases nonlinearly in the elastic segment until it decreases after reaching the neutral plane. In the elastic segment, the axial force on the pile shaft for a given time increases with the increases in the fractional order or the pile–soil interface parameter, but decreases with the increase of viscosity coefficient.

The behavior of soft soils distributed in coastal areas usually exhibits obvious time-dependent behavior after loading. To reasonably describe the stress-strain relationship of soft soils, this paper establishes a viscoelastic-viscoplastic small-strain constitutive model based on the component model and the hardening soil model with small-strain stiffness (HSS model). First, the Perzyna's viscoplastic flow rule and the modified Hardin–Drnevich model are introduced to derive a one-dimensional incremental Nishihara constitutive equation. Next, the flexibility coefficient matrix is utilized to extend the one-dimensional model to three-dimensional conditions. Then, by combining the HSS elastoplastic theory with the component model, the viscoelastic-viscoplastic small-strain constitutive model is subsequently established. To implement the proposed model for numerical analysis, the corresponding UMAT subroutine is developed using Fortran. After comparing the results of numerical simulations with those of existing literature, the reliability of the constitutive model and the program written in this paper is verified. Finally, numerical examples are designed to further analyze the effects of small-strain parameters and viscoelastic-viscoplastic parameters on the time-dependent behavior of soft soils.