Deformation Characteristics Of Subway Deep Excavation In Area With Thick Soft Soil Layer

In recent decades, on one hand, contradiction between fast urbanization ofdeveloped coastal cities and lack of land quickly increases the demand forutilization of underground space, which leads to more deep excavations in theseareas; On the other hand, however, due to complex geological conditions in coastalareas as well as the concerns of protection for the existing surroundingstructures/facilities, deep excavations in these areas are required to face challengesof controlling the potential large amount of lateral wall deflections and groundsurface settlements for the purpose of avoiding damage to adjacentstructures/facilities. For these reasons, carrying out deformation analysis of deepexcavations in coastal areas plays a significant role in theory research and practicalapplications. This study focuses on three interrelated aspects. First, based on thereview and statistical analysis of database in soft soil areas, typical deformationcharacteristics of deep excavation in thick and soft soil areas are summarized. Thenfinite element software ABAQUS is applied to model a braced excavation casehaving a thick and soft soil layer. Finally, influence of position of each strut,thickness and depth of soft soil on deformation characteristics is studied respectively.A database of case histories of wall lateral deflection and ground-surfacesettlement due to braced excavation in thick and soft soil layer are collected andanalyzed. Values of the maximum lateral deflection of diaphragm wall range from0.18%He~0.64%He, with an average value of0.38%He, where Heis the excavationdepth. Values of the maximum ground-surface settlement range from0.28%He~0.82%He, with an average of0.52%He. The lower and upper bound valuesof the ratio between the maximum ground-surface settlements and the maximumlateral deflection of diaphragm wall are0.93and1.81, respectively, with an averagevalue of1.41. Two deep excavation cases are chosen as the example to illustrate thedeformation characteristics discussed above.Detailed procedure for modeling a2D hydraulic-mechanical coupled analysis indeep excavation is presented. Then finite element software ABAQUS is applied toconduct the analysis of deformation characteristics of a deep excavation case having thick soft soil. Based on the verified model, the lateral deflection of diaphragm wall,ground-surface settlement, porous pressure and stress path are analyzed.A2D standard analysis model is applied to study the influence of thickness anddepth of soft soil on deformation characteristics. Maximum lateral deflection ofdiaphragm wall increases much with thickness and depth of soft soil; while theinfluence of thickness and depth on maximum lateral deflection is limited.Maximum ground-surface settlement also increases much with thickness and depthof soft soil, but the position of maximum ground-surface settlement changes littlewith thickness and depth of soft soil.