某软土地铁车站基坑纵向滑坡事故分析

Analyses of the Longitudinal Slip Failure during Excavation of a Subway Station in Soft Strata

狭长形地铁车站基坑在分层开挖过程中会形成临时纵向多级边坡。当挖方边坡位于软弱地层时,如果设计或施工不当将会面临基坑纵向失稳风险。针对某软土地铁深基坑纵向滑坡事故案例,在考虑参数变异性的基础上利用极限平衡法对坑内临时边坡展开调查分析,并从工程角度对土坡发生深层滑移破坏的原因进行探讨。调查结果表明:第1级边坡的坡度是影响整体稳定性的关键因素,1∶1.75(V∶H)的施工坡度不能满足下卧软弱淤泥质土条件下该局部边坡的稳定性(失稳概率高达88.92%),只有当坡度缓于1∶3时才能保证安全。为防止此类临时挖方边坡失稳,最后给出考虑土体强度参数变异性的最优边坡坡度。

During excavation of long and narrow subway station, temporary multi-stage earthen slope may appear along the longitudinal excavation side. The temporary earthen slope is at high risk of slip failure when it is designed with inappropriate side slope or it is not properly constructed, especially in soft strata. The study aims at a longitudinal slip failure case for a subway station in soft ground and analyzes the comprehensive numerical slope stability with the limit equilibrium method. It turns out that the gradient of Grade I side slope is the major factor to the global stability. The construction slope gradient of 1∶1.75(V∶H)cannot meet the stability requirement of the local slope in soft muddy substrata, the failure probability is at 88.92%. To ensure stability of the slope in soft strata,a slope gradient of 1∶3(V:H) or flatter is necessary. In order to prevent the slope instability during temporary excavation, based on the variability of soil strength parameters, the optimal slope gradient is proposed.