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首先基于工程实测,研究了大面积宽基坑土方开挖前群井预降水对支护墙变形的影响,实测到基坑开挖前降水引起的最大支护墙侧移达到15 mm,约为该基坑变形报警值的47.6%;并发现对于排桩支护墙,在支护侧布置降水井,可以起到减小坑内降水引起支护墙侧移的作用;然后开展了35个常见工况的三维流固耦合有限元数值计算,研究了基坑宽度对支护墙变形的影响规律及其机理。结果表明,宽度较大基坑在同一预降水时间和深度条件下将发生更大幅度支护墙侧移,而在通常的预降水深度(0~20 m)条件下,对于宽度为20~40 m的地铁基坑,降水引起的支护墙最大变形及其增量均对基坑宽度的变化十分敏感,而对于宽度大于40 m的基坑,在同一降水深度条件下,支护墙最大侧移仅有较小的差别。而引起上述规律的机理可用降水过程中基坑中轴两侧土体侧移的叠加效应强弱来解释,基坑宽度越小,降水过程中坑内土体侧移叠加效应越明显,最大支护墙侧移就越小。
First of all, based on engineering practice, the influence of pre-dewatering by group well pre-dewatering on the deformation of retaining wall before excavation of large-area wide-area foundation pit was studied. When the maximum supporting wall displacement caused by pre-excavation excavation reached 15 mm, The deformation value of the foundation pit is 47.6% of the alarm value. It is also found that for the piled retaining wall, the dewatering wells are arranged on the support side, which can reduce the lateral migration of the support wall due to the precipitation in the pit. Then, Dimensional fluid-solid coupling finite element numerical calculation, the effect of the width of the foundation pit on the deformation of the retaining wall and its mechanism were studied. The results show that the larger width of retaining wall will move sideways under the condition of the same pre-precipitation time and depth, while the width of the foundation pit with width of 20 ~ 40 m, the maximum deformation of the retaining wall caused by precipitation and its increment are all very sensitive to the change of the width of foundation pit, while for the foundation pit whose width is more than 40 m, under the same precipitation depth, Move only minor differences. The mechanism of the above-mentioned regularity can be explained by the superposition effect of soil lateral displacement on both sides of the central axis of the pit during the precipitation process. The smaller the width of the foundation pit is, the more obvious the side migration and accumulation effect of soil in the pit during the precipitation is. The smaller the wall displacement.