Composition of the liquid culture medium.

Coarse-grained saline soils in cold regions, characterized by poor stability and low bearing capacity, pose serious risks to road and bridge infrastructure. Microbially Induced Calcium Carbonate Precipitation (MICP) is a sustainable geotechnical technique with potential for saline soil improvement, but its efficacy is compromised by high salinity and freeze-thaw cycling. In this study, sulfate coarse-grained saline soils with varying salt contents were reinforced via MICP and subjected to multiple freeze-thaw conditioning regimes. Mechanical properties and microstructural changes of the saline soils were characterized to elucidate the degradation of MICP-treated saline soils under coupled salinity and freeze-thaw effects. Results indicate that increasing salinity exerts both inhibitory and competitive effects on MICP, reducing calcium carbonate production by 80.97%. Increased numbers of freeze-thaw cycles exacerbated damage to the cementation network. Saline soils with Na2SO4 ≥ 6% exhibited markedly reduced resistance to degradation: porosity-reduction magnitude fell to 12.27% and cohesion decreased to 0.057 MPa. Furthermore, the coupled effects of salinity and freeze-thaw accelerated the loss of MICP’s ameliorative efficacy in saline soil.

寒冷地区的粗粒盐渍土稳定性差、承载能力低下，对道路与桥梁基础设施构成严重威胁。微生物诱导碳酸钙沉淀（Microbially Induced Calcium Carbonate Precipitation，MICP）是一种可持续的岩土工程技术，具备改良盐渍土的应用潜力，但高盐度与冻融循环会削弱其改良效果。本研究针对不同盐含量的硫酸盐类粗粒盐渍土开展MICP加固处理，并设置多组冻融循环工况。通过表征盐渍土的力学特性与微观结构变化，阐明盐度与冻融耦合作用下经MICP加固的盐渍土的劣化机制。研究结果表明，盐度升高对MICP过程同时存在抑制与竞争作用，可使碳酸钙生成量降低80.97%。冻融循环次数的增加会加剧对胶结网络的破坏。当盐渍土中硫酸钠（Na₂SO₄）含量≥6%时，其抗劣化性能显著下降：孔隙率降低幅度降至12.27%，黏聚力降至0.057 MPa。此外，盐度与冻融的耦合作用会加速MICP对盐渍土的改良效果衰减。