岩溶地下工程施工抽水诱发黏土层地面塌陷机理及临界条件探讨

岩溶地下工程施工抽水容易诱发地面塌陷工程事故，目前关于此问题的研究，主要针对砂性土层，较少涉及黏土层，但大量的抽水致塌事例发生在黏土层。本文分析施工抽水对界面上黏土性质、地下水动力条件的影响，并划分出Ⅰ、Ⅱ、Ⅲ三个影响区。依据“土-水”耦合作用，在Ⅰ、Ⅱ区建立非饱和黏土地面塌陷崩解作用模式及其判据，在Ⅲ区建立饱和黏土地面塌陷潜蚀作用模式及其判据。为了应用于施工抽水实践，推导出潜水非完整孔和承压水非完整孔抽水诱发地面塌陷的临界抽水流量表达式，并计算出南宁地铁工程场地地面塌陷的临界抽水量为17.97 m3?d-1。在场地内进行的现场抽水验证性试验的结果表明此临界抽水量具有一定的工程应用性及参考借鉴意义。 

Discussion on the mechanism and critical condition of ground collapse of clay layer induced by karst groundwater pumping in underground engineering construction

In the process of underground engineering construction in karst area, pumping groundwater can easily induce ground collapse and thus leads to engineering accidents. Many researches on the issue are mainly focused on sandy soil, with limited on clay layer which usually has low permeability for groundwater flow. However, a large number of cases show that some serious collapse events are caused by pumping occurred in the clay layer. This paper discusses the mechanism and critical conditions of the collapse caused by groundwater pumping in the clay layer. Firstly, we analyses the influence of construction dewatering on the clay properties and groundwater dynamic conditions on the interface, and the affected area are divided into three areas of I, II and III. Secondly, based on the coupling effect of soil-water interaction, the mechanism of ground collapse induced by pumping water is established. In I and II area, the mechanism is disintegration, and its criterion parameter is soil water content. In area III, the mechanism is the potential erosion, and its criterion parameter is the velocity of groundwater. Thirdly, in order to establish the relationship between pumping volume and criterion parameters, the paper derives the formulas of pumping volume under two conditions, pumping phreatic water and confined water in partially penetration well, Q_cr=(V_cr lr_0)/0.16 and Q_cr=(2.33V_cr lr_0)/(0.16(arsh l/r_0 -arsh l/(3.33r_0 ))). Then, taking Nanning karst foundation pit as an example, it is calculated that the critical pumping volume of ground collapse at the site is 17.97 m3?d-1. Furthermore, the field pumping verification test was carried out in the site to verify the correctness of the value. The results show that the theoretically calculated critical pumping volume has certain engineering application and reference significance in this paper. However, more engineering examples and research are still needed to continuously improve the calculation method.