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A modeling method for the particle-based flexible membrane boundary for the drained/undrained triaxial test is proposed herein. First, the particle placement manner to construct a cylindrical membrane is described. Second, the vertical and radial stiffnesses/moduli of the entire membrane are derived and related to the interparticle contact stiffness, thereby enabling the calibration of the interparticle stiffness and correcting the confining pressure acting on the sample. Third, the application strategy of confining pressure is presented for the drained test, and a two-stage loading strategy is proposed to explore the excess pore pressure incrementally for the undrained tests. Using this membrane boundary, triaxial compression tests under the drained/undrained condition by discrete element method (DEM) were conducted on the samples with different initial void ratios and membrane stiffnesses. Simulations reproduced the behavioral transition by increasing the initial void ratio, the influence of membrane stiffness and the characteristics of shear banding, demonstrating the effectiveness of the proposed method. Differences from the referencing results with the rigid wall boundary were observed and attributed to the additional confining pressure from the membrane radial modulus, the persistence of the shear band allowed by the membrane flexibility, and the membrane penetration. © 2022 Elsevier Ltd

A modeling method for the particle-based flexible membrane boundary for the drained/undrained triaxial test is proposed herein. First, the particle placement manner to construct a cylindrical membrane is described. Second, the vertical and radial stiffnesses/moduli of the entire membrane are derived and related to the interparticle contact stiffness, thereby enabling the calibration of the interparticle stiffness and correcting the confining pressure acting on the sample. Third, the application strategy of confining pressure is presented for the drained test, and a two-stage loading strategy is proposed to explore the excess pore pressure incrementally for the undrained tests. Using this membrane boundary, triaxial compression tests under the drained/undrained condition by discrete element method (DEM) were conducted on the samples with different initial void ratios and membrane stiffnesses. Simulations reproduced the behavioral transition by increasing the initial void ratio, the influence of membrane stiffness and the characteristics of shear banding, demonstrating the effectiveness of the proposed method. Differences from the referencing results with the rigid wall boundary were observed and attributed to the additional confining pressure from the membrane radial modulus, the persistence of the shear band allowed by the membrane flexibility, and the membrane penetration. © 2022 Elsevier Ltd

This paper presents the results of a series of undrained and drained isotropic consolidated triaxial extension, tension and compression laboratory tests on lime-cement-improved very soft clay. The main objective of these tests was to investigate the material strength and stiffness properties for stress conditions similar to those expected on the passive side of excavations where a retaining structure is supported by Deep Mixing columns. The different stress paths to failure were obtained by varying the directions of the major and minor principal stresses in a conventional triaxial test cell. The undrained tests conducted at low consolidation stresses, corresponding to depths of approximately 0–10 m below the ground surface, revealed significant differences in undrained strength depending on the directions of the major and minor principal stresses, indicating anisotropic material behavior. Based on the undrained triaxial test results, the relationship among the undrained strength, the effective consolidation stress and the over-consolidation ratio (OCR) is presented for different stress paths to failure. The experimental data from the drained tests show that a failure surface comprised of a shear failure function based on the Mohr-Coulomb failure criterion and a tensile failure function based on the tensile strength and the confining stress can be applied for lime-cement-stabilized clay., QC 20191106