FAILURE MODES AND EVALUATION METHODS OF RAINSTORM-INDUCED LANDSILDES IN NORTHWESTERN HUBEI PROVINCE

In June 2003, a continuous rainstorm triggered many landslides along the main road between Yunxi to Manchuanguan in northwestern Hubei province. According to rock constituents and structures of slopes, storm-induced landslides are categorized as five typical failure models. They are (a) slip of shallow colluvial soil, (b) bedding slip along weak surfaces, (c) water split of cutting-bedding slopes, (d) failure along arc track of cataclastic rock and (e) wedge slip of block fracture slopes. The evaluation methods are proposed correspondingly in accordance with the failure modes and its effect. The shallow landslides are found to occur at ease when the water content of colluvial soil reached 85%-100% of liquid limit. Their stabilities are calculated with the infinite-slope-analysis method. The limit equilibrium method of rigid body is adopted to calculate the stability of bedding slips along weak surfaces and wedge slips of block fracture slopes. High-angle cracks of cutting-bedding slopes experienced the process from unloading, expending, water splitting to run-through failure. The split criterion of I type cracks is used for the stability analysis of cutting-bedding slopes. The stability of cataclastic rock slopes with failure trace of similar arc is calculated through Bishop's method.