岩质高边坡弯曲倾倒变形分析和破坏机理研究

弯曲倾倒常发生在反倾层状岩质边坡中，岩体表现出类似于“叠合悬臂梁”的破坏特征，呈此类破坏模式的边坡有可能会演化成为大型滑坡。以厄瓜多尔德尔西水电站左岸边坡为例，详细介绍了其地质、地貌特征，分析了施工过程中的相关监测数据。典型的反向陡倾岩体结构和特殊的岩性组成（薄层片麻岩）是该边坡发生弯曲倾倒的先决条件，而工程开挖、强降雨等外界因素触发并加剧了岩层的变形。基于离散元的数值模拟结果显示，边坡1493 m高程以下的岩体开挖会导致整个边坡发生深层的弯曲倾倒失稳。岩层变形表现出较为明显的柔性特征，倾倒体内部会发育出反向屈曲的二次折断面。边坡内塑性区的演化能够反映岩体破损区域的发展过程，最大剪应变和拉应力分布均显示倾倒破坏面呈倾角为21°的近似直线型。最后，控制边坡底部高程的开挖高度和角度能够有效降低倾倒变形的程度。

Deformation analysis and failure mechanism of flexural toppling of high rock slopes

Flexural toppling often occurs in anti-dip layered rock slopes, where rock mass shows failure behaviors similar to those of superimposed cantilever beams. Slopes in this failure mode may evolve into large landslides. Taking the left bank slope at the Ecuador’s Delsitanisagua hydropower station as an example, this paper describes its geological and geomorphological characteristics and examines the field data monitored during construction. Generally, typical rock structure (anti-dip and steep-dip) and special lithologic composition (thin-layered gneiss) are prerequisites for flexural toppling, while external factors such as excavation and heavy rainfall trigger and aggravate the deformation of rock layers. Numerical simulation using discrete elements shows that rock mass excavation below elevation 1493 m causes a deep-seated toppling failure of the entire slope; deformation of rock layers is featured with an obvious ductility, and a secondary fracture of reverse buckling develops inside the toppling mass. And in the slope mass, evolution of plastic zones reflects the propagation of rock mass rupture, and a fracture of straight failure with an inclination angle of 21° can be determined from the maximum shear strain and tensile stress distribution. Finally, control over the excavation height and angle at the slope bottom proves an effective way to reduce toppling deformation.