Laboratory investigation of suction distribution in a modified capillary barrier system

Abstract

This paper investigated the effect of transport layer in the diversion capacity of natural capillary barrier system using laboratory slope model. The slope model was constructed with stainless steel and 5 mm thick acrylic sheets. Grade VI and grade V soils classified as sandy silt of very high plasticity (MVS) and silty gravel of high plasticity (MHG), respectively were arranged in the slope model with sand and gravel transport layers sandwiched at their interface. The model was subjected to different rainfall intensities using rainfall simulator to determine the behaviour of water flow and suction distribution in the slope model. The results obtained show a modification in the suction distribution behaviour and the natural capillary barrier effect was sustained. It was also observed that a transport layer formed with gravel material was more effective in diverting the infiltrating water compared to that of gravelly sand. This occurred because the upper grade VI layer possessed capillary forces due to its finer pore structures and relatively large air entry value, thus, it retained the infiltrating water, and the gravel transport layer possessed relatively larger pore structures compared to the grade VI layer and hence it possessed higher hydraulic conductivity values and small water entry value. This arrangement, provide a capillary break and allowed the infiltrating water to flow above the interface. Therefore, the inclusion of transport layer provides a definite path through which the infiltrating water flows and diverted laterally. Thus, improving the performance of natural capillary barrier effect.