(1. Research Center of Coastal and Urban Geotechnical Engineering，Zhejiang University，Hangzhou，Zhejiang 310058，China；2. College of Resources and Environmental Engineering，Shandong University of Science and Technology，Qingdao，Shandong 266590，China；3. School of Civil Engineering and Architecture，Zhejiang Sci-Tech University，Hangzhou，Zhejiang 310018，China；4. Geotechnical and Structural Engineering Research Center，Shandong University，Jinan，Shandong 250061，China)
Abstract：Further excavation beneath the basement of an existing building is likely to change the loading stiffness of the virgin pile-soil system，thus affecting the post-excavation pile behavior. In this study，Mindlin?s solution for additional stress allowing for the variation of vertical effective stresses induced by excavation around a single pile was used. The ultimate shaft and base resistances of a pile before and after excavation were calculated according to the stress solutions. A case study was carried out on the basis of the load transfer functions of hyperbola-type along the pile shaft and below the pile base. The study involved the variation of the system stiffness and the load-displacement curves for pile-head due to excavation. Discussion was focused on the variation of reduction factors of bearing capacity with the control values of settlement，and the variation of reduction factors of the initial rigidity and the ultimate resistance with excavated depth and unloading ratio. Results show that the initial rigidity and the ultimate resistance decreased with the increasing of excavated depth，varies inversely with the unloading ratio and are smaller for weaker soils. For a given excavation depth，the decreases of the initial rigidity and the ultimate resistance are more prominent along the pile shaft than beneath the pile base，particularly for the initial rigidity. The reduction factors for bearing capacity increase with the increasing of control values of settlement until a constant value is reached.
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