Geosynthetic-encased stone columns (GESCs) represent an efficient and cost-effective solution for enhancing weak soil foundations. The deformation and load-bearing mechanisms of GESC-improved foundations under traffic flow are complicated due to substantial particle movements and soil disruption. A three-dimensional discrete-continuum coupled numerical model was proposed in this study to investigate the cyclic behavior of GESC-improved soft soil. The reliability and accuracy of proposed model was validated through experimental data. The effect of cyclic loads, bearing stratum, and geogrid encasement was investigated. Microscopic investigation of particle movement, contact force distribution, and stress transfer mechanism was performed. The vertical loads transferred from the column to the surrounding soil with the interaction effect between the aggregates and the soil. The stress concentration ratio decreased with the increase in depth. The geogrid encasement facilitated the load transfer process by effectively confining the particles and enhancing the column stiffness. The particles in the low segment of floating column exhibited large downward displacements and punching deformation. The geogrid encasement and cyclic loads contributed to enhanced compaction and coordination number of the aggregates.

Seepage plays a crucial role in the mechanical behavior and damage modes of geotechnical materials. In this work, based on the unsteady seepage equation, a hydraulic coupling numerical simulation algorithm combining interpolation finite difference method (FDM) and discrete element method (DEM) is proposed to explore the intrinsic mechanism of the interaction between geotechnical materials and the seepage process. The method involves constructing an irregular fluid calculation grid around each particle and deriving the two-dimensional unsteady seepage governing equation and its stability conditions using interpolation and the FDM. The efficiency of the seepage calculation was investigated by numerically varying the parameters of the difference format. The method was applied to simulate the generation of gushing soil in a sinking area of a sunk shaft under hydraulic drive conditions. The results indicate that the improved FDM can effectively simulate the two-dimensional seepage of soil with high calculation efficiency. The hydraulic conductivity and time step positively correlate with the calculation efficiency of the difference format, whereas the spatial step has a negative correlation. The proposed method also accurately reflects the process of gushing soil damage. These results provide a solid theoretical basis to study the geotechnical seepage field and its associated damage mechanisms.

In this paper, a recently developed unified critical state model (CASM-S), which is applicable to predict the mechanical behaviours of sand and overconsolidated clay, is numerically implemented into the Fast Lagrangian Analysis of Continua, i.e. the FLAC(3D), for engineering applications. The implicit integration algorithm incorporated with the line search method is employed to implement CASM-S model. The additional parameter u is calibrated by genetic algorithm, whilst the rest of the material parameters are determined following the literature upon applicable. Validation of CASM-S model and its numerical implementation has been well demonstrated by a series of drained and undrained triaxial compression tests conducted on clay and sand. In terms of stress-strain relations, volumetric versus axial strain, and negative pore pressure versus axial strain, the model predictions agree well with the experimental results. Then, a case study is performed to demonstrate the applicability of the CASM-S model to analyse geotechnical problems, e.g. the foundation pits excavated from Berlin sand within the FLAC(3D), where lateral deflections of the diaphragm wall and vertical displacements in a designated are evaluated. Conclusions can be drawn that the predictions of CASM-S model are almost identical to the field data, demonstrating a good performance in engineering applications.

The paper presents a refined implicit two-phase coupled Material Point Method (MPM) designed to model poromechanics problems under static and dynamic conditions with stability and robustness. The key variables considered are the displacement and pore water pressure. To improve computational efficiency, we incorporate the Finite Difference Method (FDM) to solve pore pressure, stored at the center of the background grid where the material points reside. The proposed hydromechanical MPM cannot only effectively addresses pore pressure oscillation, particularly evident in nearly incompressible fluids-a common challenge with Galerkin interpolation, but also decreases the degrees of freedom of the system equations during the iteration process. Validation against analytical solutions and various numerical methods, encompassing 1D and 2D plane-strain poromechanical problems involving elastic and elastoplastic mechanical behavior, underscores the method's resilience and precision. The proposed MPM approach proves adept at simulating both quasi-static and dynamic saturated porous media with significant deformation.

The interaction of closely-spaced footings on soils is of concern for recent decades. The inherent variability of soil makes the topic more challenging. This study investigates the behaviour of twin strip foundations on both unreinforced and geogrid-reinforced spatially random sands. The Random Finite Difference is performed by coupling Matlab and FLAC2D in each Monte Carlo simulation. Two types of sands, dense and loose, are assumed as the spatially correlated log-normal random fields and the friction angle is considered a random parameter. This study discusses how much the bearing capacity of twin footings is impressed by the heterogeneity of random sands. The unreinforced soil results show that when the uncertainty of phi is high, the homogeneous soil assumption could overestimate the interference effect by about 18% and 9% in the dense and loose sands, respectively. While soil reinforcement reduces the difference between results obtained from probabilistic analysis with those calculated with deterministic analysis. Moreover, the isotropic random fields with rapid fluctuation of phi yield the greatest interference influence in the unreinforced and reinforced dense sands. The combined impact of interference and reinforcement is greater in loose sand than in dense sand, regardless of whether the soil is heterogeneous or homogeneous.HIGHLIGHTRandom heterogeneous variability of phi on the interaction of the twin foundations on both unreinforced and geogrid-reinforced sand was investigated.For twin footings on unreinforced dense sand, Scr/B changes from 1.25 to somewhere between 1.25 and 1.5 by increasing COV phi, while on the unreinforced loose sand, Scr/B = 1 remains constant, irrespective of COV phi values.For high variability of phi, the assumption of soil without variability results in overestimation of twin footings interference effect by about 18% and 9%, which means the risk acceptance yields irrevocable damages.Increasing the number of geogrid layers, N, declines the risk of estimating the analysis with homogeneous soil, especially for high variability of phi. By all means, the footing interference and geogrid effects become lower when N is added.The interference effect is usually higher for twin footings on unreinforced sand than on the same reinforced sand. Overall, the integrated influence of interference and reinforcement in loose sand is more than that in dense sandThe combined influence of interference and the first geogrid layer is the most in the isotropic random field (theta x = theta y = 1 m) for both sand since the rapid variation of phi in both directions increases the influence and reinforcement effects.The deterministic analysis underestimates the interaction of twin foundations on the reinforced loose sand compared to the anisotropic random fields.

Particle morphology plays a crucial role in determining the mechanical behavior of granular materials. This paper focused on investigating the effects of boundary conditions on the triaxial mechanical properties of soil samples, with particular consideration given to the influence of particle shape. To achieve this, a numerical model was proposed, which couples the finite difference method (FDM) and the discrete element method (DEM) to simulate the behavior of a rubber membrane and soil particles, respectively. The particle morphology was accurately reconstructed using spherical harmonics (SH) analysis, and the shell cells in the FDM were utilized to construct the boundary modeling. Through a series of simulations, the macroscopic and microscopic mechanical responses of soil particles, both within and outside the shear band, were investigated. The obtained simulation results were then compared with those derived from the DEM simulation using a particle-based membrane. The research findings pertaining to the influence of boundary conditions and particle shape provide significant contributions to our understanding of granular material behavior. These findings offer valuable insights that can be applied in the design and analysis of geotechnical structures.

The implementation of stone columns is a widely accepted method for improving the stability of liquefiable soil. A comprehensive understanding of the behavior of the composite ground is crucial for accurate design and calculation in practical applications. Several existing mathematical models were established to assess characteristics of the stone column-improved ground by typically ignoring the vertical seepage within liquefiable soil. This negligence will inevitably lead to significant calculation errors, particularly when the vertical permeability of liquefiable sites is high or the installation spacing of stone columns is large. In this context, a new mathematical model which accounts for coupled radial-vertical seepage within liquefiable soil is proposed to determine the reinforcement performance of stone columns. The equal strain assumption and new boundary conditions are incorporated to obtain numerical solutions with the finite difference method. Then the present solution is degenerated to the conventional calculation model to verify the reasonability of the proposed model. Finally, a parametric analysis is conducted to investigate the impacts of crucial parameters on the performance of stone columns for excess pore water pressure variation during soil liquefaction. The results reveal that the peak value of the maximum excess pore water pressure ratio increases with the increment of both the column spacing and cyclic stress ratio. Moreover, the increasing radial and vertical consolidation parameters Tb and Th will accelerate the dissipation rate of the excess pore water pressure of liquefiable sites. Furthermore, the conventional model neglecting the vertical seepage will underestimate the variation rate of the excess pore water pressure, and the calculation error will become larger with the increase of Th.