Full-Scale Experimental Study on the Degradation of Pile-Supported Embankment due to Water Infiltration

Stress transfer within pile-supported embankments is influenced by soil arching, and this phenomenon is assumed to be water uptake-dependent. In this study, a full-scale model of high-speed railway pile-supported embankment was constructed to investigate the effects of water level fluctuation and long-term loading on pile efficacy (the proportion of load carried by the pile caps). The results showed that the pile efficacy decreased rapidly during the water level rising until the height of soil arching due to the stress redistribution with the pore water pressure change and the decrease of soil strength by matric suction decrease. The effective pile efficacy was expressed using the effective stress to analyze the performance of the saturated embankment below the water table. As a result of the weakening of the mechanical properties of the embankment, the critical speed was found to be 250 km/h and the effective pile efficacy decreased during cyclic loading at high water level. The effect of the matric suction on the shear strength exhibited a peak. For unsaturated sand, soil arching was enhanced with increasing suction before the peak. Accordingly, further suction resulted in minimum soil arching after the peak. As the apparent cohesion decreased with the decrease of matric suction, some degradation of the pile efficacy occurred. In practice, it is essential to consider suction effects.