基于两相流运移规律的深基坑工程漏水漏砂引发城市路面塌陷机理研究

With the large-scale development of underground space, the accident of urban road collapse induced by leakage of groundwater and sand in deep excavation engineering occurs frequently, which increases public nuisance greatly. The process from the appearance of ground cavity induced by leakage of groundwater and sand to the road collapse involve rich scientific connotation. However, the previous studies are mostly qualitative analysis, and the quantitative research based on the disaster mechanism is relatively lack. The flow of groundwater and sand during the disaster is a typically two-phase flow, which could not be correctly described by the traditional seepage-consolidation theory. The movement characteristics of the two-phase flow should be considered to investigate the disaster phenomenon deeply..Firstly, visual model tests which reflect the fluid-soil-retaining structure interaction would be conducted. Based on the test results，multi-field and multiphase coupling numerical simulation, such as FPC-CFD, would be used to research the ground movement pattern during the leakage of groundwater and sand. Besides, according to the ground movement pattern, the influence of ground loss on the security of the supporting system could be researched. The developing and collapse pattern of the ground cavity would be revealed. On the basis of the above study, a comprehensive evaluation criterion considering the ground movement pattern and the supporting system safety would be proposed. This project aims to provide the theoretical basis for the prevention, control and evaluation of this kind of engineering hazard, and it would be meaningful on promoting the security of the deep excavation.

随着我国城市地下空间的大规模开发，出现了大量由于基坑漏水漏砂引发路面塌陷的工程事故，造成了严重的社会影响。围护结构漏水漏砂形成地层空洞从而导致路面塌陷的灾害发展过程具有丰富的科学内涵，然而，以往研究多为定性分析，缺乏从灾害机理出发的定量研究。灾害过程中的水砂流动为典型的固液两相流，采用传统的渗流-固结理论难以对其进行准确描述，需考虑两相流的运移特点进行深入分析。.本课题拟进行可反映流体-土体-围护结构相互作用的可视化模型试验，并基于试验结果利用PFC-CFD等多场多相耦合方法进行数值模拟分析，得到漏水漏砂后地层运移的基本规律。在此基础上，探究漏水漏砂对基坑支护体系安全性的影响；揭示地层空洞孕育、发展及坍塌的条件。最后，提出基于地层运移规律及基坑支护体系安全性的漏水漏砂综合评价指标。本课题的研究可为此类灾害事故的针对性预防、治理及评价提供理论基础，对提高深基坑工程安全性具有重要意义。

伴随着基坑工程向“深、大、长”方向发展，其引发的重大安全事故也越来越多，大多数基坑工程灾害的发生均直接或间接与地下水有关。近年来，出现了大量深基坑工程围护结构漏水漏砂引发路面塌陷的工程事故，造成严重社会影响。然而目前相关研究大多为定性分析，缺乏从灾害机理出发的定量研究。. 本课题采用案例搜集分析、中比尺漏水漏砂可视化模型试验、离散元-计算流体力学耦合数值模拟、理论分析等多种方法开展研究。首先分析了高水压及颗粒胶结作用下水砂两相流的基本运移规律以及土体-结构动态作用机理；在此基础上，针对富水砂层中的基坑围护结构缺陷引发的水土流失问题开展研究，揭示了土体变形演化规律、水土流失量变化规律以及地下水作用机理；针对富水砂层上覆黏性土地层，再现了地层空洞孕育、发展、坍塌过程，并分析了含空洞地层的极限荷载以及地应力重分布规律；最后提出了地层损失率、漏水量突增时间因子、基坑内支撑支护体系抗扰动刚度等系列评价指标，提出了地层水土流失的评价方法。研究表明，对于富水砂层，漏水漏砂后基坑外部地表形成沉降槽，且存在着相对稳定的非影响区；地下水一方面加速土体的流失，另一方面使地层发生朝向漏点的集中运动；对于富水砂层上覆黏土地层,根据漏水漏砂后的地层应力状态可将地层分为空洞区、松动区、主拉应力区以及复杂应力区。课题研究成果对于实现基坑工程漏水漏砂灾害的科学评价、预防、治理，提高城市地下工程安全性具有较为重要的理论与实践意义。