Study On Early Waring System For Rain-induced Slope Failure In Residual Soils In Southeast Coastal Region Of China

Mountains and hills account for about 75% of the total area of southeastern coastal region in China. Because of the humid climate and rich rainfall, rock is strongly weathered and the slopes are covered by residual soil of which the structure is loose and porous. Geological hazards are triggered easily by rainfall, most of which are shallow soil landslides(account for 80% of all landslides). According to statistics, approximate 90% of soil landslides are happened during rainy season which is lasted from May to September, especially typhoon rainstorm. Because landslides triggered by rainfall lead to great loss of people life and property every year, building a waring and forecast system for landslides based on rainfall data is reqiured and valuable for practice.This article relies on Key Projects in the National Science & Technology Pillar Program during the Eleventh Five-year Plan Period:Geological Hazards in Villages Located at Mountain Area and Development of Engineering Control Techniques(ID: 2006BAJ06B02). Numerical simulation, site invetigation and data collection are used to study the issue. The main research works and conclusions are as follow:(1)According to data from site investigation, the model of the shallow soil landslide and parameters of soil are get. Then mechanism of shallow landslide is analysised by software Seep/W and Slope/W. The results show that:the potential slip surface is located at the interface between residual soil and weathered rock where the perched water will occur during rainfall; Factor of safty is related closely to pressure at the potential slip surface.(2) Intensity-Duration Curve is used commonly by previous researches to predict the landslide caused by rainfall. A theoretical method is proposed to determine Intensity-Duration Curve. Then finite element software (GEO—STUDIO) is used to study the effect of the initial moisture condition, shear strength, saturated permeability, slope angle, thickness of top residual soil layer, rain intensity and rain pattern on Intensity-Duration Curve. Results from the parametric analyses show that:Slope angle and thickness of top residual soil layer have a significant influence on the Intensity-Duration Curve. When rainfall intensity is larger than saturated permeability of the top layer, the influence of initial moisture condition and rainfall intensity is relatively insignificant. Then a risk assessment for the landslide triggered by rainfall is done with slope angle and thickness of residual soil as the factors. For each risk level, Intensity-Duration Curve is estabilished. The research findings can provide a basis on the use of Intensity-Duration Curve for predicting rain-induced landslides in residual soil slope in Southeastern coastal areas of China.(3) Based on recession law and linear reservoir model, a fomula of effective rainfall is deduced. On the assumption that the effect of different rainfall events on drainage in soil is independent, antecedent precipitation model is constructed.(4)According to antecedent precipitation model and soil moisture balance theory, Landslide Warning Index(LWI) is proposed. Then the warning system with LWI as evaluationg indicator for shallow landslide with different geological factors triggered by rainfall of is built by combining the I-D Curve and the antecedent precipitation model together.(5)A slope with hidden trouble at Wenzhou is choosen as a experimental site. The warning system for shallow landslide triggered by rainfall is applied at the site during May to Oct,2004 and Mar to Oct,2010. By analyzing and discussing the probational results, the warning system is feasible and practical to be used for forecast landslides triggered by rainfall in southeastern coastal area of China.