Experimental study on mechanical and frost heave behaviors of silty clay improved by polyvinyl alcohol and polypropylene fiber

Silty clay is widely used as subgrade filler in cold regions, which suffer from frost heave in winter and mud pumping in spring. In this study, polyvinyl alcohol (PVA) and polypropylene (PP) fiber were used to improve the mechanical and frost heave behavior of silty clay in cold regions, and the direct shear test and one-dimensional frost heave test were employed in studying improvement effects. Moreover, improvement mechanisms of PVA and PP fiber were analyzed based on test results. The main findings are as follows. (1) Both PP and PVA can heighten the strength of silty clay and suppress frost heave, but the PVA solution has a more decisive influence on improving mechanical properties than PP fiber. (2) The improvement mechanism of the PVA solution is cementing. The improvement effect of 2% PVA solution is the best, which can increase the shear strength by approximately 40%–60% at different stress levels and decrease the frost heave ratio from 0.89% to 0.16% at optimal water content. (3) For 2% PVA improved samples, 0.25% PP fiber can further increase soil cohesion by approximately 20–30 kPa at different stress levels and further decrease the frost heave ratio from 0.16% to 0.07% at optimal water content. The improvement effect is neglectable when the PP fiber content exceeds 0.25%. Overall, 2% PVA with 0.25% PP fiber is the optimum combination to improve silty clay in cold regions.