复杂地层中基坑降水引发的水位及沉降分析与控制对策

Strategy and analysis of the settlement and deformation caused by dewatering under complicated geological condition

在深大基坑工程中,若止水帷幕设置不合理,基坑内外水力联系将不能被完全截断,这样基坑内降水不但会引起坑外土体沉降,还会引发围护结构变形。在天津地铁5号线某车站基坑工程中,由于场地地层较为复杂,含水层不连续且存在大量透镜体,因此在开挖前进行了预降水试验,判断基坑内外水力联系。文章通过对预降水试验进行数据分析得出,该基坑内外承压含水层连通,且各含水层存在水力联系,原设计的落底式止水帷幕未能彻底截断承压含水层,造成了较大的围护结构变形与显著的建筑物沉降。因此,当场地承压含水层构造较为复杂时,应当在勘察阶段进行场地抽水试验,或者在基坑开挖前进行预降水试验,以全面掌握场地水文地质情况及基坑内外含水层水力联系。同时预降水前应在坑外合理设置回灌井,避免降水引发坑外沉降,并提前施工基坑第一道水平支撑,增加围护结构抗侧移刚度,减小降水引发的围护结构变形。

If the arrangement of the curtain is unreasonable in deep foundation,the hydraulic connection of both side of the foundation will still exist,which lead to the ground settlement and the deformation of the diaphragm wall.In an engineering of Tianjin 5 th metro station,the condition is complicated and many lens are discovered in the discontinuous aquifer.Pre-dewatering test was carried out before the excavation to judge the foundation hydraulic connection.This paper made an observation about the pre-dewatering test.After analyzing,it can be included that there’s hydraulic connection in both side of the diaphragm wall.The different confined aquifer has hydraulic connection,either.The confined aquifer can’t be truncated by the curtain,which caused ground settlement and clear deformation of the diaphragm wall.Therefore,in the complicated condition,pre-dewatering test before the excavation and pumping during the geological survey should be carried out to judge the connection of the aquifer and the geological condition.To decrease the ground settlement,recharge well should be built before pumping.Building the first lateral support construction can improve the lateral stiffness and reduce the deformation of the diaphragm wall caused by dewatering effectively.