泥石流堆积体边坡失稳机理的试验与稳定性分析

泥石流堆积体边坡失稳现象由于其组成物质、形成年代和堆积部位等方面的特点,与其他岩土边坡失稳有不同的表现。根据泥石流堆积体的形态特点与沉积特征,利用条块侧向推力正弦变化的Spencert条分法进行泥石流边坡稳定性的分析,对山地工程减灾分析有意义。利用Spreadsheet自嵌Visual Basic Application编译器编写了描述沿深度变化土体物理参数的稳定性分析程式。程序从确定性分析开始计算边坡稳定性系数,并利用Spreadsheet的约束优化功能寻找可能的圆弧滑动面,在此基础上计算最可能的非圆弧滑面,最后与实际观测滑面稳定性分析进行对比现场试验人工降雨造成超渗产流,实时测得的数据表明,在距表层土体50 cm以下含水量变化很小,边坡并没有产生明显的后缘张裂隙,在集中降雨导致超渗产流的情况下,泥石流堆积体边坡失稳主要是表层50 cm深度以内土体含水量变幅大的土层中发生,而在50 cm以下深度范围内土体基本保持稳定。程序分析表明,随着给定的滑动土层厚度的增加,安全系数逐步降低,只有平均土层深度为2.4 m才有完全满足约束条件的最优非圆弧滑面。研究结果表明,条分法已经不能适用于强降雨条件下泥石流堆积体边坡失稳机理的研究。

EXPERIMENT ON MECHANISM OF SLOPE FAILURE OF DEBRIS FLOW FAN AND STABILITY ANALYSIS

Failure of debris flow fan is distinct from the common rock and soil slope failure due to the unique geotechnical features of debris flow sediment.Unfortunately,this type of failure was not comprehensively and systematically studied in the past.In our recent research,according to the unique characters of debris flow fan the Spencert slicing method with varying side force inclination is used to search for the noncircular critical slip surface.This is done using Spreadsheet-automated constrained optimization.The results are then compared with the in-situ slip surface.A practical subroutine is developed to interpret the stability of slope with varying physical parameters along the depth by using Visual Basic Application embedded in Microsoft Excel.The in-situ experiment shows that the water content hardly change 50 cm beneath the slope surface and no obvious tension cracks are observed behind the slope.However in the soil layer where the actual sliding occurred,great alteration of water content under concentrated artificial rainfall happened,which is in consistent with the results of numerical simulation.With the increase in height of the soil layer,the calculated safety factor gradually decreases and an optimized noncircular slip surface with an average height of 2.4 m is obtained satisfying all the constrains and assumptions.It can be inferred that the slope failure of the debris flow fan is attributed to the dynamic seepage force caused by hydraulic gradient;and the slicing method is not suitable for the research of the mechanism of failure of debris flow fan.