Instrumented failure of hillslope models with soil-pipes

Abstract

Soil-pipes (porous pipes inside a hillslope) are often detected in collapsed slopes indicating their influence on slope failure processes. Only limited studies can be found regarding the impacts of soil-pipes on landslide mechanisms. Hillslope models prepared in a flume are experimented with different soil-pipe configurations: a) no pipe, b) closed pipe and c) open pipe. Pore-water pressures were measured at six different locations along a slope. Discharges at the outlet of soil-pipe and groundwater seepage were also recorded. For the above mentioned pipe configurations two types of experiments were conducted: a) rainfall-induced failure and b) seepage-induced failure.Experimental results show that a closed pipe accumulates water around its lower end and continuously increases pore-water pressure till a failure. An open pipe works as a means of hillslope drainage and reduces the pore-water pressure of an entire slope. However, if open pipe is blocked, pore-water pressure close to its lower end rises rapidly, leading to immediate soil mass movement. For both seepage and rainfall-induced failure experiments, the maximum pressure before the failure was larger at a slope with an open pipe (once it is closed) than a slope with a pipe closed from the beginning or that without a soil-pipe. This indicates that the blockage of soil-pipes makes a slope more susceptible to failure.Displacement vectors show that soil movement velocity close to the surface was highest at slopes with open pipes after closure and lowest at slopes without pipes because of a higher degree of saturation and pore-water pressure at the time of failure of the former. Before a large failure, small fluctuations in pore-water pressure were also observed which can be an indicator of impending failure.