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中文摘要：
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。
英文摘要：
Field observation is carried out in a large-scale excavation to obtain the wall deflection induced by pre-excavation multiple well dewatering, and the maximum deflection of 15 mm, reaching 47.6% of the allowable wall deflection for the project, is observed. As for the contiguous pile wall, making dewatering wells installed at the retained side of the wall can reduce the wall deflection during dewatering. Then, a three-dimensional soil-fluid coupled finite element model is established, and 35 numerical calculations are carried out to study the effect of excavation width on wall deflection. The results indicate that the wider excavations exhibit larger wall deflections under the same dewatering time and dewatering depth. As to the metro excavation with the excavation width of 20-40 m, the dewatering-induced maximum wall deflection is sensitive to the variation of excavation width. However, with the increasing excavation width, being greater than 40 m, the maximum wall deflection has less difference among excavations with different widths. The overlying effect of soil deflection emerging at both sides of excavation axis can account for the above-mentioned wall deflection difference among different excavations. The narrower excavation will exhibit more apparent overlying effect, and then give rise to smaller wall deflection.
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