Experimental Study of Influence of Freeze–Thaw Cycles on the Dynamic Properties of Weathered Sand-Amended Expansive Soils

Expanded soils are widely distributed in Xinjiang, China, so roadbeds will inevitably pass through the areas of the expansive soil during road construction. While Xinjiang belongs to the seasonal frozen region, subjected to a freeze–thaw cycle, mud pumping is likely to occur in the subgrade under dynamical load. To study the dynamic properties of expansive soil for a range of freezing–thawing cycles and weathered sand contents, a series of dynamic triaxial tests were performed using a medium-scale true triaxial apparatus equipped with the cyclic loading device. And the maximum dynamic elastic modulus (Edmax) and ultimate dynamic stress amplitude (σdmax) were quantitatively analyzed by the modified Hardin–Drnevich three-parameter model, on which the expression of the damage degree under the joint action of both was established. The results indicate that the dynamic performance of expansive soil is greatly affected by freezing–thawing. Under the same weathered sand content, the maximum dynamic elastic modulus and the maximum dynamic stress amplitude of soil are inversely related to the number of freezing–thawing cycles. And, those two parameters tend to be stable after the sixth freeze–thaw cycle. Under the same number of freeze–thaw cycles, the maximum dynamic elastic modulus and the maximum dynamic stress amplitude firstly decrease and then increase with the increase in the weathered sand content. The critical dosage of weathered sand is 10%, and the strength of the improved soil reached the minimum value under this context. The damage degree model that integrates the effects of freeze–thaw cycles and the weathered sand can better predict the damage degree of soil.