特殊地质环境条件研究在超大基坑支护设计中的意义——复杂地质环境下超大异形基坑支护设计优化分析

Geological Conditions Study Playing Significant Role in the Supporting Design of Super Large Foundation Pit——Optimization of the Supporting Design for a Super Large and Special Shaped Foundation Pit in Complicated Geological and Environmental Conditions

近年来,在长江下游地区地下工程建设日益增多,其基坑呈现开挖深、规模大、形状复杂等特点,由于这一地区地质环境非常复杂,其支护结构设计和施工难度非常大。本文以南京江边某特大型地下交通枢纽工程为例,探讨地质环境条件研究在深基坑支护结构设计的重要作用。该地下交通工程为地下三层结构,最下层连接过江隧道,上部两层连接附近场馆和多条地面道路,基坑开挖深、深度变化大、形态异常复杂。该工程位于南京青奥中心西侧,靠近长江岸堤。这一地区广泛分布第四系松散沉积物,近地表主要为新近沉积的软土,且厚度较大,下部为河床相砂性土,地下水丰富,且多为承压水,工程地质条件非常复杂。这里主要针对这一特大型基坑工程的核心区,分析其工程地质条件,提出可能出现的工程地质问题,结合基坑功能及形态对其基坑范围内土层从平面及剖面上进行分区和分层,以此进行基坑支护结构设计优化分析,提出采用放坡开挖(上部)和地下连续墙(下部)相结合的支护设计方案,有效解决大型异形基坑群施工技术难题,而且施工速度快、建设成本低。这一研究成果对于长江下游地区类似特大型异形超深基坑的支护及施工设计具有积极借鉴意义。

Objectives： In recent years, along with the increasing of underground engineering constructions, which presents deep excavation pit, large scale, complex shape and other characteristics. The geological environment is very complicated in the lower reaches of the Yangtze River, as a result, the supporting structure design and construction is very difficult. Taking a large underground transportation hub project along the Yangtze River in Nanjing as an example, the paper discusses the important role of the research of geological environment on the design of the supporting structure of deep foundation pit. The structure of the project has three layers. The bottom layer would connect river bottom tunnel, and the upper two layers would connect nearby venues and a plurality of ground road. The foundation pit excavation is very deep, the excavation depths are very different and the shape of foundation pit is very irregular. The project is located on the west side of Nanjing Youth Olympic Center, the place that is near the Yangtze River embankment. The Quaternary loose sediments are widely distributed in this area. Methods： This paper aims at the core area of the super large foundation pit engineering, analyzes its engineering geological conditions and raises the possible engineering geological problems. According to the function and shape of the foundation pit, the soil layer of the foundation pit is partitioned and layered from the plane and section and the supporting structure design has been optimized. The scheme of foundation pits supporting was a combination method of open cut excavation in the upper part and the diaphragm wall in the lower part. The successful completing and deformation monitoring of foundation pit has illustrated the rationality of the design scheme. Results： It solves the problem of large irregular foundation pit construction technology, improves the construction speed and reduces the construction cost. Conclusions： This result can be applied for the design of support scheme and deformation control of some super large foundation pit engineering in the area of the Yangtze River.