Abstract: The excess pore water pressure in silty sand ground is difficult to dissipate and may easily lead to soil liquefaction under wave and seismic loadings. Microbially induced carbonate precipitation (MICP) is an emerging technique for anti-liquefaction soil reinforcement. In this study, a series of undrained hollow cylinder torsional shear tests was carried out. The development of dynamic pore water pressure in saturated MICP-treated silty sand under axial-torsional coupled cyclic shear loads was investigated, considering various influencing factors. Results indicate that the development patterns of dynamic pore water pressure in MICP-reinforced silty sand can be categorized into types A, B, and C. These patterns transition from type A to type C with increasing MICP reinforcement cycles, cyclic resistance stress ratio, and relative density. Based on the experimental test data, a modified model for predicting the dynamic pore water pressure in MICP-reinforced silty sand is proposed. This model is then verified using the test results from this study and also existing literatures. A good agreement between test data and predicted values is obtained, demonstrating the accuracy and applicability of the model. This study provides a reference for the dynamic stability analysis of MICP-reinforced soil and the formulation and optimization of anti-liquefaction soil reinforcement schemes.

Key words: microbially induced carbonate precipitation (MICP), silty sand, undrained cyclic torsional shear test, cyclic resistance ratio, modified dynamic pore water pressure model