Dynamic parameters of subgrade soils prone to mud pumping considering the influence of kaolin content and the cyclic stress ratio

Abstract

Rail transport industry often desires to increase the freight capacities for heavy-haul trains to transport more goods. However, this requires an increase in the axle loads, which results in the railway foundation being subjected to higher cyclic stress ratio (CSR), causing significant subgrade distress. Recent laboratory investigations indicate that addition of kaolin to low-to-medium plasticity soils can avert early softening and fluidization of the soil under increasing CSR, how the dynamic parameters such as the shear modulus (G) and the damping ratio (Dp) of soils may change consequentially to this modification needs appropriate quantification. Furthermore, while there are plenty of studies correlating shear strain and plasticity index (PI) with the dynamic properties of the soil, the role of loading parameters such as the CSR and number of cycles (N) has not been thoroughly investigated. Therefore, efforts have been made to characterise the dynamic parameters of moderately plastic silty-clay soils with varying kaolin content (cK) and loading parameters. The results indicate that as CSR exceeds a critical level, G decreases rapidly whereas Dp was found to increase abruptly in few loading cycles. The paper also shows that when G diminishes about 20% from its initial value, any further loss in shear modulus would cause soil to turn into an unstable stage where the excess pore water pressure and shear strain begins to increase rapidly. Although varying the kaolin content does not alter the PI significantly, it causes a considerable effect on the dynamic parameters of the soil. Based on the current experimental findings, empirical models are proposed to estimate dynamic parameters of subgrade soils prone to mud pumping considering loading condition under heavy haul railways.