鄂西北山区降雨型边坡失稳模式和评价方法

2003年6月的一次连续降雨诱发了鄂西北山区郧漫公路沿线多处边坡失稳。根据边坡岩土体的组成和结构特征，总结出了5种典型的暴雨型边坡失稳模式：浅层堆积体滑移、含软弱面顺层滑移、切层边坡水压劈裂破坏、碎裂岩似弧形追踪破坏和块裂岩楔体滑移。根据边坡破坏特点和降雨作用形式提出了相应的评价方法，认为浅层堆积体在暴雨下含水量，即85%~100%液限含水量时易发生滑移，通过平面无限斜坡评价法计算边坡稳定性；含软弱面顺层边坡及块裂楔形体均为剪切滑移失稳，采用简化的刚体极限平衡法计算其稳定性；切层边坡中陡倾裂缝经历了卸荷张开－水压开裂－贯通破坏的过程，通过Ⅰ型裂缝扩展判据评价边坡稳定性；碎裂岩边坡发生类似弧形滑移的追踪破坏，采用连续介质圆弧法计算边坡稳定性。

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.