Threshold stress and deformation characteristics of clay subgrade for railway tracks

Clay subgrade beneath railway track experiences stress of cyclic nature that can result in progressive shear failure at a stress level lower than the clay monotonic strength. This paper described the effective stress analysis of threshold stress and the deformation characteristics from a series of cyclic undrained triaxial tests carried out on reconstituted kaolin clay, which simulates the behavior of clay subgrade under cyclic loading conditions due to the loading of passing trains/vehicles. Cyclic loading frequency typical to that experienced by railway track foundations near subgrade surface was employed. In addition, a critical state model is proposed for predicting threshold stress of saturated clay under undrained cyclic compression without resorting to lengthy laboratory testing. Validated by observed tests data, the model provides a lower-bound solution of the threshold stress of clay subgrade for rail tracks, from the measured values of fundamental soil properties, based on consolidation history and current state of stress