The Analysis Of Soil Behavior Under Layered Dewatering And Excavation Inside A Super-deep Foundation Pit

Dewatering and excavation are layered and alternated during deep-pit excavation, this process can cause changes in effective stress and the deformation of the soil in the foundation pit . Therefore the soil behavior will be changed considering the differences between dewatering and excavation. At present there are few studies about this subject. The research works in this paper are based on Tianjin transfer junction station and also considered the construction sequences, some productions were worked out in the research of the soil behavior on layered dewatering and excavation inside a super-deep foundation pit .The major achievements are as follows:(1)A series of triaxial stress path test were performed on the Tianjin soft silty clay and silty soil considering the effect of preconsolidation pressure by dewatering on the soil in the deep foundation , in order to simulate the layered process of dewatering and excavation inside a super-deep pit . The tests' results show that the process of dewatering can reduce the resilience deformation of soft soil during excavation. In each step of the excavation, the soil resilience considering the role of dewatering (ignore compaction effect) is larger than which only considering the excavation, in its ratio of between 2.0-2.5. The soil effective stress increases, leading to consider the process of dewatering .And at the each step of excavation the resilience deformation considering the process of dewatering was significantly larger than only considering the role of the excavation. In addition, the deformation time rebound effect can not be ignored in soft land area.(2) Triaxial stress path test through a combination of seepage test simulation were carried out to study the seepage of soil behavior through the process of dewatering and excavation. Excavation simple comparision, considered the impact on dewatering after the seepage coefficient reduced by 12 percent, so that the pressure of dewatering for the effects of soil permeability or have a certain impact.(3)The deformation of soil inside the pit was analyzed by FLAC3D program to consider the process of dewatering whether or not in the excavation of a foundation pit. And three main effective factors such as depth of excavation, soil properties and even the wall to the depth were taken into account.(4)Taking into account the behavior of deformation in super-deep excavation induced by the soil anisotropic characteristics , with triaxial tests and consolidation tests, analyzed the initial anisotropy of soft soil in Tianjin.Samples were cut with different inclination to the sediment plane and its maximum principal shear stress and poor initial tangent modulus in undrained triaxial shear test are different.(5)Based on the monitored data from Tianjin transfer junction station ,some analysis of results were summed up. The behavior of foundation deformation (including pile settlement inside the pit, the settlement of the wall and the surrounding buildings) considered the construction steps. In particular, the the focus of the study is the effects of soil deformation induced by the layered process of dewatering and excavation inside a super-deep foundation pit.