堰塞坝水力驱动溃滑过程模拟方法研究

Simulation Method of Hydraulically Driven Breaking-sliding Process for Landslide Dam

为评估堰塞坝安全,需要分析其受水力驱动溃滑导致的溃决变化过程。传统的分析方法或没有运用极限平衡法,或认为溃滑过程中其滑裂面倾斜角度不变,或没有考虑孔隙水压力。实际中,堰塞坝水力驱动溃滑过程是一个需要由极限平衡理论解决的问题。通过采用岩土工程中圆弧形式的边坡稳定分析方法,考虑孔隙水压力影响,运用总应力法和有效应力法模拟堰塞坝不断溃滑的过程(包含溃口横向的不断扩展过程及其垂直下切过程);开发DBS-IWHR的电子表格分析堰塞坝溃滑过程,该电子表格已被耦合到溃决洪水分析电子表格DB-IWHR,用于分析其受水动力驱动溃滑导致的溃决洪水变化过程。结果表明:1)DBS IWHR提出确定堰塞坝水力驱动溃滑过程的模拟步骤:确定特定圆弧滑面的安全系数FS;在各种可能的滑裂面中,确定与最小安全系数Fm相关的临界滑裂面;确定与Fm=1相关的坡脚失稳的临界深度;连续溃滑过程的模拟。以上过程只需手动4步即可进行溃滑过程模拟,基于VBA编制的程序具有良好的交互性,利于读者和使用者进行矫正和二次开发。2)选取唐家山案例,分析了水动力驱动溃滑过程及溃决洪峰流量过程,其洪峰为6 500 m^3/s,溃口宽度为150 m;预测的溃决洪峰流量为7 610 m^3/s,溃口宽度为139.6 m。预测值与实测值的误差在允许范围内,验证了改进的水力驱动溃滑过程模拟方法的可靠性。

Valuating breach flood of landslide dam is usually through analyzing the breach process caused by hydraulically driven breaking-sliding process.The traditional analytical method does not use the limit equilibrium method,or the slope angle of the slip surface is not changed during the collapse process,or the pore water pressure is not considered.In fact,the hydraulically driven breaking-sliding process is a problem that needs to be solved by the limit equilibrium.An approach to determine the critical slip surface by analytical method with circular slip surfaces,the effective and total stress methods dealing with different dam materials,and a procedure to model the stepped failures of the breaking-sliding process due to continuous toe cutting were proposed.A spreadsheet entitled DBS–IWHR was developed to the breaking-sliding process analysis.This spreadsheet was incorporated into another spreadsheet entitled DB–IWHR for the calculation of flood hydrograph caused by hydraulically driven breaking-sliding.Research indicated that DBS–IWHR proposed a simulation step to determine the hydraulically driven breaking-sliding process of the dam,which included finding the factor of safety for a specific circular slip surface FS;among a variety of possible slip surfaces,determining the critical one associated with the minimum factor of safety Fm;determining the critical depth of toe cutting associated with Fm=1;modeling the stepped breaking-sliding process.The simulation of the collapse process could be performed in four steps manually.The spreadsheets are transparent and self-explanatory,easy for practitioners to understand and check for secondary development through the web.The de veloped approach was tested by back analysis of the Tangjiashan landslide dam breached in 2008 with a flood peak of 6 500 m^3/s,breach width of 150 m.The predicted flood peak is 7 610 m^3/s and the breach width is 139.6 m.The calculated results of the final breach base level and the peak discharge were in good agreement with the field data.Further,the results were shown to verify the reliability of the improved hydraulically driven breaking-sliding process simulation method.