天津某地铁车站深基坑突涌事故分析

Analysis on deep foundation pit water inrush accident of a subway station in Tianjin

基坑施工过程中渗漏、突涌水灾害时有发生,地下水处理不当是引发基坑事故的重要影响因素之一。突涌事故往往发生于土方开挖等施工阶段,具有突发性、难以可视化的特点。基于分析天津市某地铁车站基坑工程的突涌水事故的现场实测数据、处理措施等内容,回溯事故发生原因,主要是开挖基底下的承压层减压降水效果不明显,通过围堰反压、注浆、混凝土封堵等措施,配合启动基坑外承压层降水井进行减压降水,有效控制了突涌水事故。基坑开挖施工期间,须严格监测基坑内外水位,发现异常须及时排查原因解决,现场人员须加倍重视。当基坑采用悬挂式止水帷幕且坑内没有条件进行减压井施工时,可利用基坑外观测井进行降水减压,但应避免引发周边环境的地层大范围沉降、土层不均匀沉降等,必要时采取相应措施加以保护。

The water leakage and inrush disasters occur from time to time during construction of foundation pit engineering,and improper treatment of groundwater is one of the important factors causing foundation pit accidents.The water inrush accidents often occur in the construction stage such as earth excavation,which is sudden and difficult to visualize.Based on the analysis of on⁃site measured data and the treatment measures for water inrush accident of a subway station foundation pit engineering in Tianjin,the causes of this accident were reviewed.The main reason is that the effect of pressure relief dewatering in confined aquifer under the base of foundation pit were not obvious.Through the measures of cofferdam reverse pressure,grouting,concrete sealing and so on,and in cooperation with initiating the dewatering well of the confined aquifer outside the foundation pit,the water inrush accident was effectively controlled.During the excavation of foundation pit,the water level inside and outside the foundation pit must be strictly monitored,the causes of abnormalities must be investigated and solved in time,and the field staff must pay more attention.When suspended impervious curtain is adopted for foundation pit and there is no condition for relief well construction in the pit,the observation well outside the pit can be used for pressure relief dewatering,but the large⁃scale settlement and differential settlement of soil layer in the surrounding environment should be avoided.If necessary,corresponding measures should be taken for protection.