强降雨条件下含软弱夹层粘性土坡稳定性分析

Stability analysis of cohesive soil slope with weak interlayer under heavy rainfall

为了分析含软弱夹层粘性土坡在强降雨条件下的稳定性,结合某失稳边坡工程现场实际调研资料,基于饱和非饱和渗流与非饱和抗剪强度理论,提出了一种新的含软弱夹层粘性土坡稳定性分析方法,并利用该方法分析了强降雨条件下边坡的渗流特性及安全系数变化规律。分析结果表明:降雨入渗先在边坡软弱夹层内形成暂态饱和区,且当坡顶入渗的雨水未渗流至软弱夹层时,夹层内暂态饱和区中的雨水会沿夹层上表面向着坡顶方向渗流;降雨入渗过程中,边坡基质吸力与铅直有效应力之间存在严格的正相关变化关系;随着降雨历时的增加,塑性区首先在软弱夹层内部贯通,然后向坡顶扩展,边坡安全系数逐渐降低;降雨停止一段时间后,由于坡顶入渗雨水的补给,软弱夹层内局部将仍存在暂态饱和区,此时,塑性区面积会由坡顶向软弱夹层内部减小,再由夹层内部至坡面逐渐缩减,但边坡安全系数并未明显上升;根据数值计算结果可将粘性土坡失稳过程分为夹层软化、夹层挤压、拉伸裂缝、坡顶沉降和断裂滑移等5个阶段。因此,为了降低强降雨对边坡稳定性的影响,在含软弱夹层粘性土坡支护设计时应着重考虑边坡排水系统的合理布设。

For the stability analysis of cohesive soil slope with weak interlayer under condition of heavy rainfall,a new method is proposed based on the slope investigation data and the fleory of unsaturated seepage and shear strength to analysis the seepage characteristics and variation of safety coefficient for soil slopes containing weak interlayers.Analysis results indicate：due to rainfall infiltration,the transient saturated zone is formed in the weak interlayer of slope;Under rainfall infiltration process,there is positive correlation between the suction and the vertical effective stress;With increase of rainfall duration,theplastic zone extended from the inside interlayer to the top of slope,as a result of which the slope safety coefficient decreases;After rain,weak interlayer will still exist in local transient saturated zone,causing less significant decrease of the slope safety coefficient.According to the numerical results,the instability process of cohesive soil slopes can be divided into 5 stages：interlayer softening,interlayer extrusion,tensile crack,slope crest settlement and fault slip.Consequently,to minimize the influence of heavy rainfall on the slope stability,reasonable drainage system should be emphasized in the design of cohesive soil slope with weak interlayer.