Dewatering induced subsidence during excavation in a Shanghai soft deposit |
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| Authors: | Ye-Shuang Xu Huai-Na Wu Bruce Zhi-Feng Wang Tian-Liang Yang |
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| Institution: | 1.Key Laboratory of Land Subsidence Monitoring and Prevention,Ministry of Land and Resources,Shanghai,China;2.Shanghai Engineering Research Center of Land Subsidence,Shanghai,China;3.School of Naval Architecture, Ocean, and Civil Engineering,Shanghai Jiao Tong University,Shanghai,China;4.Department of Geotechnical and Tunnelling Engineering, School of Highway,Chang’an University,Xi’an,China |
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| Abstract: | Foundation dewatering has become a major cause of land subsidence in Shanghai. The burial depth of foundations in relation to geotechnical construction works is less than 75 m, and the corresponding groundwater includes phreatic, low-pressure artesian, and the first confined aquifers. Based on the geological and hydrogeological conditions beneath Shanghai, methods of dewatering may be divided into three modes and further five patterns according to the insertion depth of the dewatering-retaining system. The most common dewatering mode aims to reduce the water pressure in the confined aquifer by setting the dewatering wells inside the pit, whilst the retaining walls are buried in the confined aquifer and partially cut off the confined aquifer layer. To predict the settlement due to foundation dewatering, numerical models are generally adopted, which are similar to those used to predict land subsidence induced by regional groundwater withdrawal; however, since foundation dewatering is conducted along with the setting of retaining walls and foundation pit excavation, which differs from regional groundwater withdrawal, interactions between the retaining wall-dewatering well, the dewatering-excavation, and dewatering-recharge are important factors affecting the analytical model. Since the grading of the shallow soil layers is different, stratified settlement characteristics of the shallow soil strata and seepage erosion, which results in additional deformation, need to be given particular consideration. |
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