坑外降水条件下软土地层深大盾构工作井稳定性研究

采用合适的计算方法确定有效的围护方案是基坑设计中的难点。以南京纬三路过江隧道江北盾构工作始发井为依托，采用空间地基板法反演分析得到各地层m值，通过编制DLOAD子程序实现主动区与被动区的判别和相应荷载的施加，得到坑外降水条件下软土地层深大盾构工作井围护体系的受力与变形特征。计算结果与现场实测值较为吻合，从而证明采用空间地基板法配合反演得到的地层m值可有效预测工作井围护体系的变形与受力特征。为进一步优化设计方案，选定连续墙厚度、支撑截面尺寸及底板以下5 m范围内土体m值3个参数，通过正交试验进行参数分析，得到影响连续墙水平位移及支撑轴力的主要因素。计算方法及相关计算结果可为同类工程设计提供参考。

STUDY OF STABILITY OF DEEP SHIELD WORKING SHAFT IN SOFT SOIL STRATA UNDER CONDITION OF DEWATERING OUTSIDE SHAFT

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.