HCA Study of Permanent Deformation of Sand Under Train-Induced Stress Path Considering Variable Confining Pressure

In this paper, a typical stress path experienced by subsoil in a railway foundation is used in a dynamic hollow cylinder apparatus (HCA) to obtain cyclic responses of soils subjected to moving trainloads. This is achieved through varying axial force, torque, inner and outer confining pressures independently during each load cycle. A multistage test using the specific stress path is conducted on Leighton Buzzard sand considering various magnitudes of the trainloads. Comparative studies using constant confining pressures are also carried out. It is found that in both cases with constant or variable confining pressures, the long-term deformation mechanism of the sand tends to change from shakedown to incremental collapse as the load level is increased. It was noticed that the increase rates of vertical permanent strain of the two cases are close if they have similar maximum ratios of deviator stress to mean effective stress (q/p)_max and ratios of peak deviator stress to average mean effective stress q_max/p_avg.