雨水软化下路基土质边坡失稳模式及判别阈值

Failure modes and discriminating thresholds of soil subgrade slopes due to rain softening

为了提高雨水软化条件下路基土质边坡稳定性分析的准确性,开展路基土质边坡失稳模式及其判别准则分析,提出边坡失稳随软化深度wz增加依次呈现单位土条式、组合式及整体式3种模式;采用滑体长度L与软化深度z_w的比值λ作为表征参数,确立界定3种失稳模式的2个阈值λ_（cr）和λ_f;基于刚体极限平衡条件,构建以组合式失稳模式为基础且涵盖3种失稳模式的边坡稳定安全系数统一表达式。研究表明：单位土条式与组合式失稳模式转化阈值λ_（cr）和组合式与整体式失稳模式转化阈值λ_f受坡体强度参数及几何参数影响并不显著,范围分别为15.2~20.0和3.0~6.3;λ〈λ_（cr）时采用单位土条式顺坡平面失稳模式忽略滑体上下缘滑体力学作用会得到偏于保守的结果,λ〉λ_f时采用以圆弧滑面为代表的整体式曲面失稳模式则偏于危险,而λ≤λ_f时采用对数螺旋形和圆弧形的整体式曲面滑动模式差异不大。

In order to improve the accuracy of stability analysis of slopes under the condition of rain softening,the modes and criterion of failure of soil slopes of road subgrade were analyzed. For the different rain softened depths,three types of failure modes occurred including soil slice type of unit width,composite type,and integral type. The ratio l of the length of slip body to the softened depth was taken as the characterization parameter of deep and shallow slope failure category,and the thresholds λ_（cr） and λ_f of three modes were presented. According to the limit equilibrium condition of rigid body,a unified formula of stability safety factor based on the composite type failure mode was established. The results show that threshold lcr of unit width soil slice type and composite type and threshold λ_f of composite type and integral type are not significantly affected by the strength and geometric parameters of the slope,and are between 15.2–20.0 and 3.0–6.3 respectively. If λ was less than λ_（cr）,applying the parallel slope-plane mode produced the conservative results due to the ignoring of the mechanical effect of the upper and lower edge. If λ was more than λ_f,applying the integral curve represented by circular slip surface yielded larger safety factor. But if λ was less than λ_f,applying the logarithmic spiral or circular arc sliding mode yielded no significant difference.