Dynamic resilient modulus of heavy-haul subgrade silt subjected to freeze-thaw cycles: Experimental investigation and evolution analysis

To investigate dynamic resilient modulus (MR) of heavy-haul subgrade silt, especially in seasonal frozen regions, a series of dynamic triaxial tests were performed after various freeze-thaw (FT) cycles. The specifically designed loading sequence was proposed for determining MR, which reflected the stress characteristics of subgrade induced by heavy-haul traffic load. Furthermore, the effects of numbers of FT cycles, initial moisture content, freezing temperature, deviator stress and confining stress were comprehensively considered as state variables. The results revealed that MR showed a decreasing trend with increase of numbers of FT cycles, where the attenuation stages for dynamic resilient modulus were divided into three stages, namely, rapid attenuation, slow attenuation and gradual cessation of attenuation. Then, the increase of initial moisture content and decrease of freezing temperature led to a decrease in MR, where the higher initial moisture content was, the more obvious deterioration effect was. Meanwhile, when the freezing temperature decreased to-15 degrees C, the appearance of the freeze shrinkage effect inhibited the damage to the soil skeleton, and the attenuation trend of MR was alleviated. The ensuing discoveries were that confining stress and deviator stress had hardening and softening effects on the thawed silt, respectively, leading to the increase and decrease in MR. In particular, when the initial water content was higher, the softening effect caused by deviator stress was more significant. To enhance the practicability, the predicted model for determining MR was proposed that included the coupled effects of the above variables. Furthermore, the fatigue life of typical asphalt pavement structures was calculated considering the damaged dynamic resilient modulus of silt subgrade duo to the freeze-thaw cycles. The outcomes illustrated that fatigue life of pavement structures with semi-rigid and flexible base reduced by 17.5% and 22.5%, respectively, via adopting the dynamic resilient modulus values under maximum attenuation state. This study could supply meaningful reference for safe and sustainable design of heavy-haul subgrade and asphalt pavement in seasonal frozen regions.