Abstract: The underground rail transit has become an important infrastructure project type to solve the urban congestion and to form one of the major urban contexts. The deep excavation process often induces soil stratum deformation, which in turn might adversely affect the surrounding environment. This paper presents the case history of the Baidang South Station of Suzhou Metro deep excavation response supported by Soil Mixing Wall (SMW) columns. A typical section was selected to conduct that real-time monitoring data analysis on the axial force of the inner support, the vertical/horizontal displacement of the top of the retaining wall, the horizontal displacement of the retaining wall, the groundwater level and the ground surface subsidence. The results indicate that: 1) The supporting axial force in the supporting structure showed an overall increasing trend during the excavation process, and the supporting force would gradually transfer to the lower portion of the structure; 2) The top of the retaining wall showed a trend of horizontal displacement towards to direction of excavation, and with the deep excavation was becoming more and more pronounced. With the deeper excavation, the stress state inside and outside the excavated area changes, and the soil at the bottom of the excavation heaves, causing the retaining wall to show an overall uplift trend; 3) During the deeper excavation, the retaining wall shows a swelled belly shape, and with the excavation, the position of the maximum horizontal displacement of the retaining wall gradually moved down to the vicinity of the excavated bottom; 4) The surface settlement values of the most measuring points continue to accumulate, and gradually become flat after the completion of the excavation, and the maximum surface settlement is about 0.16% of the depth of the excavation, indicating that the SMW method column has a good applicability in deep excavation supporting in the thick silty clay soils.

Key words: Deep Excavation, SMW Method Column, Silty Clay, Monitoring