Engineers Australia

Cyclic Response of Railway Subgrade Prone to Mud Pumping

Mandeep Singh, Buddhima Indraratna, Cholachat Rujikiatkamjorn and Richard Kelly

Abstract

Given the fast pace of growth in today’s world, the need for a cost-effective and sustainable mode of transportation is indispensable. Railways provide a mode of mass transportation which facilitates travel between two places. Rails are often laid on subgrade soils with difficult conditions such as low bearing capacity, and high groundwater tables, etc., so when trains pass over these challenging ground conditions, the subgrade softens into a slurry and starts pumping the fines into the upper ballast layers. In Australia, this phenomenon is commonly known as mud pumping or mud holes. This paper investigates the cyclic response of subgrade prone to mud pumping. It is observed that the cyclic stress ratio (CSR) has a threshold value beyond which the cyclic axial strains and mean excess pore pressures rapidly accumulate. An empirical model is proposed to capture the generation of mean excess pore pressure in relation to the applied CSR. Further, numerical simulations have been carried out using PLAXIS2D to model vertical drain inclusions in the railway subsoil. The results indicate that vertical drains not only reduce the accumulation of excess pore pressure but also assist in their dissipation under cyclic loading, thereby providing a viable alternative to mitigate the effects of mud pumping.