Establishment of Criteria for Traffic Regulations Along the National Road Based on Numerical Simulations During Torrential Rainfall

In this study, the risks for slope failure were evaluated by numerical simulations and the new criteria for announcing traffic regulation during rainfall were established. Firstly, the saturated-unsaturated flow analysis was performed by 2-D Finite Element Method (FEM) and the flow simulation results were used for the circular arc sliding computation for slope stability. The criteria for announcement of traffic regulation for a certain slope along the national road were established using the relation between rainfall in short time (hourly rainfall and/or rainfall every 10 min) and accumulated rainfall, when the safety factors calculated from circular arc sliding computation become lower than 1.0. The risk of the slope failure was assessed by drawing snake curves (plotting rainfall in short term against the accumulated rainfall) using previous torrential rainfall data. In the simulations, the effect of different rain intensity based on the rainfall every 10 min and/or 1 h recorded by Japan Meteorological Agency on the rainwater infiltration into the slope as well as slope stability were also investigated.