Failure investigation of a geosynthetic-reinforced soil slope subjected to rainfall

This paper presents a comprehensive failure investigation of a geosynthetic-reinforced soil (GRS) slope subjected to rainfall. The investigated slope is a 26-m high, four-tier, geogrid-reinforced structure backfilled with low plasticity silty clay that contains more than 60% of fines. The GRS slope first exhibited excessive deformation after typhoons and heavy rainfall from 2010 to 2012. The slope collapsed in 2013 due to two sequential typhoon events with a total accumulated rainfall of more than 600 mm. The slope failed in a compound failure mode in which the failure surface partially cut through the reinforced zone and partially passed along the interface between the weathered sandstone and intact shale. By using the recorded rainfall, site geology, and measured soil and reinforcement parameters, a series of coupled hydro-mechanical finite element analyses were performed on the basis of the unsaturated soil mechanics to examine the failure mechanism and factors triggering the slope failure. The numerical results indicated that the slope failure occurred due to the development of positive porewater pressure within the reinforced zone and retained weather sandstone layer. Observations and lessons learned from this case history are discussed and remedial measures to improve the overall slope stability are proposed and evaluated.