Numerical Analysis Of Excavation Characters In Top-down Construction And Bottom Upheaval For Deep Excavation

Since its lots of advantage, top-down construction method (TDCM) has widely been used in underground engineering and municipal engineering. The research on the technology of top-down excavation will prompt the development of pit engineering.In this paper, the construction process was simulated with FEM numerical method, and some specialty and law in TDCM are analyzed, such as diaphragm walls'horizontal displacement, the settlement and discrepancy settlement between diaphragm walls and pillars or project piles, the bottom upheaval and the force characteristics of piles; the result of TDCM and traditional construction method has been contrasted and analyzed; and then the two important design parameter(the depth into the earth and the thickness of wall)of the diaphragm walls were optimized and adjusted with reiterant calculation and analysis. The main results as follows:(1). Based on the soft soil in Tianjin, this paper is conducted the multi-storey soil upheaval testing, and analysis of the relationship between the rebound rate, resilient ratio and resilient modulus, which used in analysis of the calculation of Rebound parameters.(2). Excavation for the Uplift-pile using TDCM were analyzed, and the side friction of Uplift-pile in TDCM , relative displacement of the relationship between the soil and the pile, differential equations of side friction can be used as the Uplift-pile reference design .(3). The horizontal displacement of diaphragm walls with within the excavation pit to unload is gradually increased, but because of the strong level of support floor, making follow-up support from the floor in the status of the location of displacement of almost no increase, and the displacement of walls below the support values have different levels of increase.(4). The results of this paper is that the actual design and construction process of the diaphragm walls'thickness and embedment ratioλshould be limited to a certain scope of the right, embedment ratioλin the 0.5 to 0.8, the walls'thickness at 800 ~ 1000 mm are reasonable, can meet the design requirements of the project.