Field Tests at Tunnel Location on Problematic Soils

High speed trains running in tunnels laid on erosive soil deposits experience mud pumping as one of the major problems among others. The pore water pressure generated due to cyclic loading induced by running trains causes seepage flow. The seeping water carries loosened soil particles from beneath the railway track to the surface via invert weep holes. This causes uneven deformations and cracks in the concrete railway track which requires costly and difficult maintenance, time and again. From the knowledge gained from laboratory experiments on newly developed experimental set-up simulating the erosive soil subjected to cyclic loading beneath railway tracks, it is observed that mud pumping problem can be avoided in the field if the invert weep holes are relocated at some distance away from the point of application of cyclic load. Elaborate instrumentation and monitoring during the full scale model tests carried out near the tunnel construction site in the town of Kamitome in the Kagoshima province, Japan, established that a permissible 1.5 m elevation of the weep holes on the tunnel walls is sufficient to stop the mud pumping problem.