Three-dimensional Numerical Analysis Of Zhoushan Coastal Soft Soil Deep Foundation Pit And The Research Of Constitutive Model Selection

Soft soil is widely distributed in the coastal area, high void ratio, high compressibility is its characteristics. Big deformation of retaining structure, big surface subsidence around the pit and big uplift at the bottom of the pit can be easily caused in the foundation pit engineering, especially in the large-scale deep foundation pit engineering. Offshore soft soil is very different because of different area and different reasons for the formation of soft soil, its physical and mechanical properties has obvious regional characteristics. This paper start from the theory of constitutive model of soil, contrast and analysis calculated values and measured values of the foundation pit displacement with the Midas GTS under the background of Zhejiang Zhoushan immersed tube tunnel south and north bank foundation pit engineering, the results shows that Modified Cambridge constitutive model is more superior in the numerical simulation of offshore soft soil deep foundation pit construction. The model parameters value range is analyzed combining with the measured value and calculated value. The main work and conclusions in this paper are as follows:1, according to introduce of a handful of the constitutive relation of soil model, such as elastic model in the linear elastic model, the Mohr-Coulomb (MC) model in the bomb-ideal plastic class model, the modified Cambridge (MCC) model in the strain hardening model, etc, which are widely used in current commercial geotechnical software, compared their applicability in the deformation of the soil of soft soil foundation pit construction.2, Contrast and analyse the Mohr～Coulomb (MC) model simulation results, the modified Cambridge (MCC) model simulation results with the measured results of the north shore excavation engineering east1in Zhoushan immersed tube tunnel engineering, the results show that modified Cambridge model can predict soil displacement of foundation pit better.3, The reasonable range of three parameters, normal consolidation line slope (lambda), over consolidation line slope (kappa) and the critical state line slope(M) in the modified Cambridge (MCC) model are researched depending on the north shore excavation engineering east1in Zhoushan immersed tube tunnel engineering. Contrast and analyse the simulation results of horizontal displacement of the pit, surface subsidence around the pit and uplift at the bottom of the pit with the measured results, reach conclusion shows that the reasonable range of normal consolidation line slope (lambda) is0.0561～0.0881, the reasonable range of over consolidation line slope (kappa) is0.01395～0.01705, the reasonable range of critical state line slope(M) is0.67572～0.82588. 4, Analysis and calculation of Zhoushan immersed tube tunnel south coast soft soil deep foundation pit engineering is done with three dimensional numerical simulation. The soft soil constitutive model use modified cam-clay model, the corresponding parameters are choosed from the reasonable range which are put forward in this paper. The displacement characteristics of soil is analyzed Combining with the displacement contours. The simulation results of horizontal displacement of the pit, surface subsidence around the pit and uplift at the bottom of the pit are in good agreement with the measured results, the applicability of the modified Cambridge (MCC) model in coastal soft soil deep foundation pit’s deformation numerical simulation is further validated, the results verify the range of the three parameters in modified Cambridge (MCC) model which are put forward in this paper are reasonable at the same time.