(1. Research Center of Coastal and Urban Geotechnical Engineering，Zhejiang University，Hangzhou，Zhejiang 310058，China；2. Engineering Research Center of Urban Underground Development of Zhejiang Province，Hangzhou，Zhejiang 310058，China；3. China Railway 11th Bureau Group Co.，Ltd.，Wuhan，Hubei 430061，China；4. Institute of Geotechnical Engineering Science，Hohai University，Nanjing，Jiangsu 210098，China； 5. Zhejiang Province Architectural Design and Research Institute，Hangzhou，Zhejiang 310058，China； 6. Hangzhou Metro Group Limited Company Co.，Ltd.， Hangzhou，Zhejiang 310020，China；7. Zhongtian Construction Group Co.，Ltd.，Hangzhou，Zhejiang 310020，China)
Abstract：Taking a 30.2m deep and large basement excavation in Hangzhou soft clay as the research object，the excavation performances，including the stress of diaphragm walls，the displacements of columns，the axial force，earth pressure，the settlements of ground surface and utility pipelines，are thoroughly investigated based on the collected 16 excavation cases in Hangzhou and the data published in literature about similar excavation in Shanghai. Following conclusions are obtained：(i) The location of the maximum wall deflection is between Hm = He-5 and Hm = He-+ 2.5. Benefit from the excellent integrity of the retaining systems，the maximum wall deflection is well controlled with average value 0.28%He. (ii) Due to the“corner effect”，the deflection of the walls located at the excavation center is 3.5 times of that located at corner，suggesting that the“corner effect”is significant to restrict deflection for the excavation without adopting the zoned excavation technique. (iii) The diaphragm walls and ground surface produce the maximum displacement increment in stage 6 due to the“creep effect”of Hangzhou soft clay and the “depth effect” of deep excavation. The excavation of soil buried in deep can release more stress and induce greater displacements than the excavation in shallow. (iv) The horizontal struts mainly carry the load due to the removal of the soil nearby in the proximity，and the excavation has a slight influence on the distant struts. The transferring of the excavation -induced loads to the struts are completed in 1–2 months after strut casting. (v) Different from trapezoid or AEP triangle envelope distribution mode，the horizontal earth pressure behind the diaphragm wall of the considered project is linearly distributed along with the depth. The ground adjacent to the excavation surface is more likely in an active state and generates smaller horizontal earth pressure. (vi) Based on the 30.2 m deep excavation and the collected 16 similar excavation cases in Hangzhou，an empirical relation between the excavation area and the maximum wall deflection is proposed.
