Investigating frozen strength characteristics and their relationship with microscopic pore structure of chloride silty clay improved by cement

Cement improvement often serves to enhance the soil strength and reduce the occurrence of projecting mud soil and water gushing during the construction of tunnel. However, strata after cement improvement are still vulnerable to seawater leakage issues caused by high pore-water pressure and this leakage possesses a huge threat to the tunnel safety. Artificial ground freezing (AGF) technology is effective in reducing the strata permeability. This article evaluates the mechanical behaviour of the chloride silty clay improved by cement by the unconfined compressive (UC) test. The relationship between the strength and micropores of chloride silty clay was investigated by using mercury intrusion porosimetry (MIP) test. Test results revealed that soil stress–strain relationship can be well characterised by the Duncan-Chang and strain-softening models. It was found that when chloride silty clay improved by cement undergoes freezing, the strength decreases by up to 60% as the salt content increases from 0% to 3%. A three-way ANOVA revealed that the influence of temperature on the unconfined compressive strength was the most significant. For every 0.1% increase in soil porosity, the UCS decreased by 1.058 MPa. At different cement ratios, the soil strength showed an exponential trend of decline with an increase in porosity.