软弱地层深大基坑富水特性及组合支护控制

为研究深大基坑地层富水特性以及组合支护方案下基坑控制效果,以在建连云港—镇江高速铁路线淮安东站站前广场基坑为工程背景,开展含水层抽水试验,明确地层富水特性以及水力联系,为基坑施工提供依据;设计地连墙、TRD两种支护以及分层开挖方案,并开展了基坑控制效果现场监测分析。结果表明：(1)影响含水层渗透性因素较多,应采用多种方法比对分析,获取较为合理的水文参数;本工程含水层潜水静水位标高+6.60～+6.80m,第Ⅰ承压含水层静水位标高+3.73m~+3.75m,潜水和承压水之间有较厚的弱透水隔水层,两者之间没有明显的水力联系。(2)地连墙和TRD连接处深层水平位移最大,需要加强重点防控;地连墙侧位移分布近似均匀,TRD墙侧呈现上、中部大,下部小的“刀把”形,地连墙侧水平位移以及地表沉降控制效果均优于TRD墙侧。(3)桩顶和立柱隆沉具有明显的三阶段变化特征,支护方案对桩顶和立柱隆沉的影响差异较小;混凝土撑轴力和基坑外水位变化具有明显的四阶段变化特征;支护方案对第1道混凝土支撑即次支撑轴力的影响较大,最大轴力差异为18.8%;对第2道混凝土支撑即主支撑轴力的影响基本忽略,差异为0.7%。

Research on water rich characteristics and combined support control of deep and large foundation pit in soft stratum

In order to study the water rich characteristics of deep and large foundation pit and the control effect of foundation pit under the combined support scheme, the foundation pit of Huaian East Station Square is taken as the engineering background. The aquifer pumping test is carried out to clarify the water rich characteristics and hydraulic connection of the stratum, so as to provide the basis for the foundation pit construction; two kinds of support schemes of diaphragm wall, TRD and layered excavation are designed, and the field monitoring and analysis of foundation pit control effect is carried out. The results show that: (1) There are many factors affecting the permeability of aquifer, so a variety of methods should be used for comparative analysis to obtain more reasonable hydrological parameters; in this project, the static water level elevation of aquifer is + 6.60 ~ + 6.80m, and that of the first confined aquifer is + 3.73m ~ + 3.75m. There is a thick weakly permeable aquiclude between phreatic water and confined water, and there is no obvious hydraulic connection between them. (2) The horizontal displacement of the deep layer at the joint of diaphragm wall and TRD is the largest, which needs to be strengthened; the displacement distribution of the diaphragm wall is approximately uniform, and the TRD wall side presents a "knife handle" shape with large upper and middle parts and small lower part. The horizontal displacement and surface settlement control effect of the diaphragm wall side are better than those of the TRD wall side. (3) The uplift and settlement of pile top and column have obvious three stage variation characteristics, and the influence of support scheme on pile top and column settlement is small; the axial force of concrete bracing and the water level outside the foundation pit have obvious four stage variation characteristics, and the maximum difference of axial force is 18.8%; the influence on the axial force of the second concrete support, that is, the main support, is ignored, and the difference is 0.7%.