都江堰市五里坡高位滑坡-碎屑流成因机制分析

2013年7月10日发生的四川省都江堰市中兴镇三溪村五里坡滑坡-碎屑流，属于典型的降雨型高位斜向层状岩质滑坡-碎屑流灾害。在前人研究成果梳理和进一步野外调查的基础上，分析总结了五里坡滑坡-碎屑流的成因及演化模式，并对五里坡高位滑坡在降雨作用下的后缘裂隙扩展判据和滑坡启动判据进行了定量计算。研究表明，五里坡滑坡的演化模式为后缘拉张裂隙形成→降雨作用下裂缝开始扩展→动、静水压力联合作用下斜坡沿泥质软弱层滑动→后缘拉裂槽形成→“7?10”强降雨诱发滑坡复活→滑体前缘临空崩落、加速→崩滑体沿沟谷铲刮、运移→堆积停止。从力学角度推导了前期降雨作用下滑体后缘裂缝自动扩展的最小深度、滑坡失稳的临界水头高度和临界降雨强度的计算公式，得出充满水的后缘裂缝在静水压力作用下开始自行扩展的临界深度为11.3 m；后缘裂隙贯通至滑带后，当五里坡斜坡体在后缘裂缝水头高度达到9.8 m时滑坡处于启动的临界状态。

Formation mechanism analysis of Wulipo landslide-debris flow in Dujiangyan city

On July 10, 2013, a high-position landslide-debris flow was triggered by the heavy rainfall at Wulipo Sanxi village, Dujiangyan city, Sichuan province. The landslide-debris flow caused serious damages to Sanxi village. On the basis of further field investigation and previous research results, the formation mechanism and evolution process of the Wulipo landslide-debris flow are analyzed. Considering the actual mechanical behavior of the Wulipo landslide, the crack extending criterion under hydrostatic pressure and landslide start-up criterion under rainfall are calculated. The results show that the evolution process of the Wulipo landslide-debris flow includes following steps: formation of unloading crack, crack extending under hydrostatic pressure, slope sliding along the potential sliding surface under the effects of both hydrostatic and hydrodynamic pressures, rift trough forming, landslide reactivation due to heavy rain, rock blocks falling and accelerating, shoveling and moving along the valley, stacking and stop moving. By deducing minimum depth of water in the crack leading to crack automatically developing, critical water height in back crack and critical rainfall intensity causing slope instability, it is concluded that the crack could automatically develop when the depth of water in the crack reached 11.3 m; and the slope would lose its stability once the height of the water level in back crack reached 9.8 m.