Numeric Simulation And Analysis Of The Influence Of Pit's Surrounding Environment Induced By Dewatering

At present, it is usually effective and economical in excavation in silt-sand soil layer that draining ground water or reducing the difference of water head by light pumping wells or other equipments in order to increase the stability of the pit. However, the lowering of water table will cause harmful subsequent settlement and influence the building and municipal facilities which are near the pit. This problem has caused the attention of many technicians and scholars, but it has not been deeply studied or successfully attacked. Therefore, it is necessary to systemically study the mechanics of the influence induced by dewatering. In this paper, some aspects of this problem were studied as followed.Based on the two-dimensional unsteady seepage flow theory, a finite element equation was present, then the Initial Flow Method which is very beneficial for the coupled analysis problem was introduced for the computation of the phreatic surface because the same FEM grid had been used for stress and seepage calculation.By the law of conservation of mass, the principle of effective stress and the Darcy's law as well as the equilibrium differential equations, a coupled mathematic model that included the terms of source and sink, and its corresponding direct coupled FEA model, for the analysis of groundwater seepage and stress were developed. The coupled characteristics of the pit's environment induced by dewatering were analyzed by the software ABAQUS.By the two-dimensional FEA, the law of the fall head curve, the radius of the influence and the settlement were thought to be related with the Young's module, permeability and the depth of dewatering, etc. then the characteristics of the fall head curve, the radius of the influence and the settlement were analyzed in sequence. By the FEA model that the recharge effect had been taken into account, the surface settlement and the surface differential settlement of the ground surface which was out of the recharge position could be greatly reduced, the recharge effect at far foundation pit wasmuch more apparent than at the near position. By the FEA model that the water-seal effect had been taken into account, the surface settlement and surface differential settlement of the ground surface could be largely reduced; the reduction of the total settlement and the differential settlement increased as the length of water-seal wall grew.The two-dimensional FEA model was applied to the computation of a case project. The measured results compared favorably with the numerical results that verified the feasibility of the coupled model.