High-strength salt-tolerant mineralisation strain and microbial reinforcement mechanism of saline soil

Soil reinforcement and improvement based on microbial-induced calcium carbonate precipitation (MICP) technology in highly saline–alkaline environments has emerged as a new research focus in geotechnical engineering. However, the effectiveness of MICP is often limited by issues such as soil porosity, microbial cell size, weak compatibility between calcium carbonate crystals and soil particles, and the low environmental tolerance of conventional urea-hydrolysing bacteria. These factors represent critical bottlenecks in applying MICP to fine-grained and highly saline–alkaline soils. In this study, a high-yield urease strain, designated ZN1#, was isolated, and its potential application in MICP for saline soil was investigated. The mineralisation products, growth characteristics, urease activity, solidification effect, unconfined compressive strength (UCS), shear strength, calcium carbonate content, and soluble salt content of the solidified soil were evaluated. Results indicated that ZN1# strains exhibited a broader environmental tolerance than traditionally mineralised strains under chloride, sulfate, and chloride-sulfate mixed salt conditions. Saline soil columns treated with ZN1# achieved superior compressive and shear strengths, with UCS increasing by 16.23 times, cohesion by 13.48 times, and the internal friction angle by 1.92 times compared to untreated saline soil. Furthermore, comparing the curing strength under different soil particle groups, it was found that the ZN1# enhanced performance in finer soils, particularly in silty clay, where curing strength reached 4.397 MPa. Additionally, the total soluble salt content in saline soil reinforced by ZN1# decreased by 13.14%. This study demonstrates that ZN1# holds significant potential for application prospects in microbial reinforcement of saline soils, soil improvement, and fine-grained soil reinforcement. By overcoming the limitations associated with the environmental tolerance of traditional mineralised strains, this research provides a novel and sustainable strain for MICP technology. It introduces a new paradigm for its application in fine-grained soil.