Characterizing the dynamic resilient modulus of subgrade soil treated by BT-SAP subjected to freeze-thaw cycles

Abstract

Freeze-thaw (FT) cycles are regarded as a damage effect to the dynamic resilient modulus (MR) of subgrade soil in seasonal frozen regions and improving the resistance on freeze-thaw cycles must be concerned urgently. For this purpose, the bentonite superabsorbent polymer (BT-SAP) was developed as an available admixture to relieve the attenuation of MR of subgrade soil under FT cycles. In order to evaluate the improvement of resistance on FT cycles, a series of dynamic triaxial tests were conducted after various FT cycles. The main influences on MR were investigated including the numbers of freeze-thaw cycles, BT-SAP contents, deviator stress and confining stress. The experimental results indicate that the BT-SAP can delay the attenuation trend of MR that means the resistance on freeze-thaw cycles have been promoted. The ensuing discoveries are that with the increment of BT-SAP content, the sensitivity of the subgrade soil to FT cycles is gradually reduced. Nevertheless, results reveal that a proper content of BT-SAP is recommended as 0.5%, where if the BT-SAP content exceeds 0.5%, the improvement effect of resistance on FT cycles decreases. Moreover, the improved effect caused by BT-SAP can produce a coupling enhancement combining with confining stress, and it also can offset the softening effect due to the deviator stress. For better application and practicability, the high-accuracy empirical model for predicting MR is established and validated. Finally, based on the soil freezing temperature, unfrozen moisture content and moisture distribution characteristics, the mechanism of BT-SAP reducing the freeze-thaw cycle sensitivity is analyzed. The conclusions mentioned above show that employing BT-SAP material is acceptable and significant to improve resistance on freeze-thaw of subgrade soil.