Cyclic loading response and associated yield criteria for soft railway subgrade – Theoretical and experimental perspectives

Abstract

Heavy haul rail transport certainly demands a more robust and stable railway foundation as the subgrade soils are prone to instability at higher axle loads. The current paper presents a series of cyclic triaxial tests to investigate the response of different subgrade soils with varying cyclic stress ratio (CSR). Theoretical models based on the Modified Cam Clay (MCC) model are extended to predict the experimental results. Two different hypotheses are proposed and discussed in this paper, namely, Model A: yield surface changes its size, and Model B: yield surface changes its shape, during cyclic loading. The results indicate that when CSR exceeds a critical threshold (CSRc), the excess pore water pressure (EPWP) and axial strain (εac) increase rapidly as the number of cycles (N) reaches a certain critical level (Nc,i). This causes soil instability and leads to specimen failure. At the same level of CSR, the faster the cyclic load is applied (i.e., at higher frequencies), the greater is the number of cycles required to trigger soil instability. The proposed models predict the inception of soil instability under cyclic rail loading with reasonable accuracy for Australian heavy haul track conditions.