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Abstract It is difficult to choose an appropriate calculation method to determine the effective enclosure system in foundation pits design. This case study deals with the excavation of Jiangbei shield working shaft of Weisan road over-river tunnel in Nanjing，which is a typical deep working pit in soft soil strata. The spatial foundation plate method was used to analyze the deformation and stress condition of the structure of the shield working pit under dewatering outside the foundation pits. The m values of strata are obtained through back analysis；and the active and passive areas were judged by the DLOAD subroutine. The calculation results are consistent with the measured results；so the spatial foundation plate method with m values from back analysis can effectively predict the deformation and stress behavior of the enclosure structure. In order to further optimize the structure，three factors，i.e. thickness of diaphragm wall，size of supporting section and m value of soils within 5 m below the floor，are selected for orthogonal array experiment；and the main influencing factors of horizontal displacement of diaphragm wall and axial forces of bracings are obtained. The calculation method and the relevant results can provide references for similar engineering.
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Received: 17 September 2012
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2013, Vol. 32 
