Laboratory modelling on sand erosion caused by tunnel leakage in water-rich sandy strata

When deep underground tunnels are built in water-rich sandy strata, seepage erosion induced by unexpected leakage frequently occurs and can progress to severe ground subsidence or ground collapse. Observations from most accidents indicate that erosion does not lead to severe ground subsidence in uniform sandy strata if emergency actions are taken in a timely and proper manner; however, several catastrophic accidents reveal that the sand erosion rate is significantly accelerated when the leakage point is initiated in composite sandy strata near the interface between fine and coarse sand layers. Unfortunately, very limited research has been conducted to compare the sand erosion caused by tunnel leakage in various sandy strata. In this study, a laboratory testing apparatus is designed to analyse the evolution of seepage erosion due to leakage in various water-rich sandy strata. The flow paths of the eroded particles are carefully investigated, and observations of the sand behaviours are recorded throughout testing. The laboratory test and observation results reveal the development of cavity shape and indicate that the evolution of erosion is influenced by the particle diameter, sand distribution, leakage location, and hydraulic head.