Research On Time Characteristic Of Construction Deformation And Security Of Deep Excavation In Soft Clay Area

The problem of soft soil creep will not only influence the deformation control of deep excavation, but also is very important to the safety characteristics, which is quite serious in those excavation with high deformation control requirement. The deformation pattern of the soil mass and supporting system is quite complex due to diversity of the surrounding environment. Starting from the mechanism of creep and taking the influence of time into account, this paper developed an elastic-viscose-plastic constitutive model and performed detail study and discussion on the deformation safety and time characteristic using numerical analysis. It mainly involves the following parts:1. Brief review and conclusion of the study status of soft clay rheological characteristics, including the methodology employed, the knowledge acquired, etc. Meanwhile, on the basis of elastic-plastic constitutive model, the paper developed an elastic-viscose-plastic constructive model which could explain the creep characteristic of soft clay by introducing a hysteretic deformation item which decomposes the non-elastic strain into instantaneous plastic strain and hysteretic plastic strain.2. With the help of the secondary development program interface provided by FLAC^3D, numerical analysis of the elastic-viscose-plastic constructive model was implemented, and was compared with the result calculated by modified Cambridge model inhered in FLAC^3D, which verified the feasibility and validity of the developed model.3. Practical formula of the rebound of excavation was suggested aiming at the construction condition of adjacent subway station deep excavation. A numerical method was employed to investigate the deformation regularity of the surrounding soil mass and the deformation pattern of the station structures, and compared with the deformation regularity under Greenfield condition.4. The deformation expressions were given with/without surrounding overload condition. Simplified method for the deformation of the soil caused by deep excavation was given. Three-dimensional numerical analysis was carried out towards the station; the deformation pattern under surrounding overload was studied and compared to that under non-overload condition.5. To study the normal excavation, timly supporting and overbreak in the course of deep excavation construction, allowable deformation of wall was used as safety index. The change regulation of the security time characteristics of deep excavation was quantitively studied, and the safe standing time of two situations was obtained. Last, the susceptivity analysis of influence factors of the surrounding overload was carried out, including construction deformation and security of deep excavation under the influence of the different overload magnitude, distance, depth and width.