Recently, the biostimulation has received attention due to its sustained mineralization, environmental adaptability and lower cost. In the current study, a series of isotropic consolidated undrained triaxial shear (CU) tests were performed on biocemented soil treated through biostimulation approach to examine the effect of cementation levels on the undrained shear behaviors. The test results demonstrate that the biocementation generated by the biostimulation approach can improve the shear behaviors remarkably, with the observed changes in stress-strain relationship, pore water pressure, stress path, stiffness development, and strength parameters. The variations of the strength parameters, i.e., effective cohesion and effective critical state friction angle, with increasing cementation treatment cycles can be well fitted by an exponential function and a linear function, respectively, while the variation of the effective peak-state friction angle is relatively small. The increased shear strength, stiffness, effective cohesion, and strain softening phenomenon of biocemented soils are related to the densification, increased particle surface roughness, and raised interparticle bonding caused by biostimulation approach. The liquefaction index decreases with the increase in cementation treatment cycles, especially at lower initial mean effective stress (100 and 200 kPa), indicating that the biostimulation approach may be a viable method for anti-liquefaction of soil.

Typical soil solidifiers, such as ordinary Portland cement, have a limited solidification effect when used as solidifiers, and they can cause significant environmental pollution during the manufacturing phase. Therefore, a relatively green and environmentally friendly solution based on magnesium sulfate cement (BMSC) is explored as a solidifying agent for solidifying the soil. The present paper undergoes a systematic compaction experiment, an unconfined compressive strength test, and an unconsolidated undrained triaxial shear parameters test of BMSC solidified soil with different magnesium oxide (MgO) contents when BMSC was used as the soil stabiliser and the physical properties of BMSC solidified soil were analysed by the techniques ofX-ray diffraction (XRD), scanning electron microscopy-energy spectrometry (SEM-EDS), XAn analysis was conducted on the mechanical properties and microstructure of BMSC solidified loess. When the molar ratio is determined, the maximum dry density increases with the increasing magnesium oxide doping. The results indicate that the compressive strength of BMSC solidified loess increases with the increase in the MgO content. Specifically, the compressive strength of the 6 % BMSC solidified loess specimen increased by 528 % compared with that of the pure loess specimen. Moreover, the maximum deviation stress increased by 236.54 %, while the cohesion and internal friction angle increased by 221.89 % and 44.27 %, respectively. The XRD and-ray computed tomography (X-CT), and mercury intrusion porosimetry (MIP). SEM/EDS analyses revealed a great number of 517 (5Mg(OH)2-MgSO4-7H2O) whiskers crisscrossing between the soil particles, which made the microstructure of the BMSC solidified loess specimen denser. The MIP results showed that the macropores and porosity reduction decreased from 43.30 % of the pure loess to 37.01 % in the 6 % BMSC solidified soil specimen. Similarly, the X-CT results revealed a higher pore density and larger porosity in pure loess.

Conventional CFD (Computational Fluid Dynamics)-DEM (Discrete Element Method) coupling methods encounter apparent difficulties in addressing the large deformation exhibited by soils with arbitrarily shaped fluid domains for undrained triaxial shear tests with flexible membranes. Herein, a novel CFD-DEM coupling method is proposed to address the main challenges of dynamically reproducing complex external boundaries and mapping for fluid fields. The workflow of surface mesh construction, mesh coarsening, and internal volume division is proposed to generate required meshes. The mapping of fluid information between updated and original meshes is implemented by a distance-weighted interpolation strategy. The coupling method is subsequently applied to investigate the effect of flexible membranes with and without clamped ends on undrained triaxial shear characteristics of soils after its comparison to the constant volume method for validation. The flexible membranes without clamped ends are proven to delay the shear dilation and weaken the inter-particle contact force. Moreover, they enable the free development of the shear band and induce significant octahedral shear strain at both ends of the band. The fluid pressure distributions of both boundary types are uniform and a vortex-shaped velocity field for the fluid is obtained due to the effect of the particle-fluid interaction.