(1. Key Laboratory of Geological Hazards on Three Gorges Reservoir Area，Ministry of Education，China Three Gorges University，Yichang，Hubei 443002，China；2. College of Civil Engineering and Architecture，China Three Gorges University，Yichang，Hubei 443002，China；3. State Key Laboratory of Disaster Prevention and Mitigation of Explosion and Impact，
Army Engineering University of PLA，Nanjing，Jiangsu 210007，China)
Abstract：The application of Microbially Induced Calcite Precipitation (MICP) technology to improve geomaterials has become a significant research focus. However，studies on the resistance of treated soils to wet-dry cycles and the analysis of their deterioration mechanisms are still limited. Therefore，this study focuses on granite residual soil treated with microbial improvement and designs wet-dry cycle tests under typical environmental conditions. Comprehensive mechanical tests and microstructural analysis were conducted to systematically analyze the changes in mechanical properties and deterioration mechanisms of the microbially improved granite residual soil under wet-dry cycling. The results indicate that：(1) Under the influence of wet-dry cycles，the compressive strength and shear strength of the treated soil exhibit a deterioration trend that is initially rapid but gradually slows down. After 30 cycles，the compressive strength，cohesion，and internal friction angle decrease by 56.73%，38.73%，and 24.66%，respectively. The deterioration is faster during the first 12 cycles，while it significantly slows and stabilizes thereafter；(2) The porosity，density，and P-wave velocity of the treated soil exhibit a change pattern consistent with the mechanical parameters due to the dissolution of calcium carbonate cement and feldspar minerals under wet-dry cycles；(3) Microstructural analysis reveals significant improvements in the pore structure of the treated granite residual soil，with increased compaction and a marked reduction in interconnected pores. During wet-dry cycles，the dissolution of calcium carbonate cement and feldspar minerals in some interconnected pores leads to a slight increase in porosity. However，the calcium carbonate within enclosed pores remains intact，and the kaolinite produced from feldspar dissolution reacts with calcium ions to form aluminosilicate precipitates that fill and block pore channels. Consequently，the microstructural changes and the deterioration of the physical and mechanical properties of the treated soil under wet-dry cycling tend to stabilize. These research findings and insights provide valuable references for the application of MICP technology in improving granite residual soils.
