Mechanical Properties of Microbially Mineralized Soils under Freezing and Thawing Cycles

To investigate the stabilization effectiveness of microbially induced calcium carbonate precipitation on frost damage in subgrades within seasonally frozen regions, this study used subgrade soils from the Xige section of the Qinghai Tibet Railway around Qinghai Lake. Under varying numbers of grouting rounds, we examined the permeability characteristics, the thermal characteristics, and soil deformation under freezing and thawing cycles. The results show that, relative to the untreated specimens, the permeability coefficient of the specimens after 9 grouting rounds decreased by 2 orders of magnitude, and the thermal conductivity increased by 347.22%. After 7 freezing and thawing cycles, frost heave displacement decreased by 60.84% and the frost heave ratio decreased by 60.32%. The calcium carbonate content after 9 rounds increased by 245.4% compared with 1 round. Based on these results, microbially induced calcium carbonate precipitation can effectively enhance the engineering performance of the seasonally frozen subgrade around Qinghai Lake and provides a new approach for subgrade reinforcement in seasonally frozen regions.