白鹤滩水库初次蓄水对双河段岸坡稳定性的影响预测分析

Prediction and Analysis of Influence of the First Impoundment of Baihetan Reservoir on the Bank Slope Stability of Shuanghe River Section

以白鹤滩库区巧家县双河左岸土质岸坡为研究对象,通过野外详细调查、现场钻孔剪切试验以及SEEP&SLOPE模块耦合分析,针对该岸坡在未来蓄水后的稳定性问题进行预测分析。研究发现:双河左岸土质岸坡主要由残坡积角砾土组成,其对水敏感性较强,饱水后角砾土内聚力降低60.65%,内摩擦角降低40.0%,内聚力受影响程度大于内摩擦角。当水位由当前状态先升至765 m,再升至825 m时,渗流场反应明显,坡体稳定性系数由1.238降至1.098,再降至1.010,降幅先大后小,坡体由稳定状态过渡欠稳定状态后处于失稳临界状态。岸坡土体在库水作用下发生的结构损伤、强度衰减是岸坡稳定性恶化的主要原因,其变形趋势将由蠕滑变形向整体失稳破坏发展;在此过程中,库水的反压作用对于岸坡水下部分具有有利作用,促使岸坡受影响,高程段缩减。

The stability of the left-side soil bank of the Shuanghe River in Qiaojia County in Yunnan,SW China after impoundment of the under-construction Baihetan reservoir was simulated and predicted via detailed field investigation,field drilling shear test,and the Seep&Slope module coupling analysis.The soil bank slope is mainly composed of residual deluvial breccia soil that is highly sensitive to water.After water saturation,the cohesion of breccia soil would be decreased by 60.65%,the internal friction angle decreased by 40.0%,and the degree of influence of cohesion would be greater than that of internal friction angle.Results show that when water level rises to 765 m and then 825 m from the current level,the slope stability coefficient will decrease from 1.238 to 1.098 and then to 1.010,the decline amplitude increase first and then decrease,and the slope will be in a critical state of instability after the transition from stable state to unstable state,showing very obvious changes of the seepage field.The structural damage and strength attenuation of the bank slope soil under the action of reservoir impoundment will be the main reasons for the deterioration of the bank slope stability,and the deformation trend will develop from creep deformation to the overall instability,during which the backpressure of reservoir water will have a favorable effect on the underwater part of the bank slope,and thus reduce the affected elevation section of the bank slope.