The Stress Performance Analysis And Three-dimensional FEM Simulation Of Double Large-diameter Ring Beam Support System

Ring beam support system is a new support structural type developed infoundation pit excavation engineering, and it has been used in the eastern regionwidely in recent years. Compared with the other supporting systems, ring beamsupporting system has many advantages such as proper distribution of stress, effectiveutilization of underground space, smaller quantities, few requirements on geometricalform of pit and widespread use. So it can be applied to foundation pit excavation insoft soil area. Double large-diameter ring beam support structural system wasemployed in deep excavation of pit in Tianjin Cause Bay Plaza constructionengineering and this kind of support system's stress and its deformation are socomplex. By construction monitoring in excavation, data about internal force ofsupporting system and soil horizontal displacement are obtained. This thesis analyzesthese data and also discusses the characteristic of internal force change in ring beamand influence on environment in the course of excavation. By these analyses, we canacquire the law of horizontal displacement in ambient soil, and the measuresconsidering the construction factors can be adopted for the ring beam support systemdesign and its popularization. Although computation theory of deep foundation pit has already made rapidprogress, the sophisticated computation theory was not established in double ringbeam support system. Three-dimensional FEM analysis has been widely used infoundation pit excavation engineering. In this thesis, ANSYS was adopted to simulatethe ring beam support system in Cause Bay Plaza foundation pit excavationengineering. In the analysis, soils, fender piles and horizontal double ring beambracing structure were considered as a whole body and elastic-plastic D-P model wasadopted and the interaction between soils and bracing structure was taken into accountalso. The comparation between construction monitoring data with the computingresult of many kinds of construction conditions illuminates 3-D nonlinear FEM is aneffective approach to simulate foundation pit engineering when the factors concernedwere chosen properly. This thesis also analyzes influence of soil modulus andexcavation sequence on the internal force change and deformation and put forward theappropriate excavation plan, and, based on which, more feasible and economicmeasures can be adopted for the design and construction of foundation pit.