Triaxial compression experiment and damage constitutive model of microbially modified strongly weathered phyllite

Microbial improvement of strongly weathered phyllite roadbed can effectively solve the problems of insufficient filling and waste soil in roadbed construction while protecting the environment and considering economic benefits. This paper uses microbially induced carbonate precipitation (MICP) technology to improve the strongly weathered phyllite in the Nanchang area and conducts the porosity and triaxial compression tests on the samples before and after the improvement. According to the strain strength theory of rock and the Druker-Prager yield criterion, the damage constitutive model of the improved sample is established considering the effects of the initial porosity and cementation degradation coefficient on the sample's mechanical properties. The results show that the strengths of the samples improved by MICP technology are increased by more than 35%, and the po-rosities are reduced by 15%, which meets the requirements of roadbed filling. The stress-strain curves of the modified samples under triaxial compression can be divided into three stages: elastic stage, elastic-plastic stage and ductile flow stage. The triaxial compression test results of the improved samples show that the damage constitutive model established can describe the stress-strain relationship of the samples well, which verifies the rationality of the model. This model provides a theoretical basis for studying damage softening and mechanical properties of microbially modified strongly weathered phyllite samples.