Finite Element Numerical Calculation Of Seepage And The Application In Foundation Excavations

The calculation of water inflow in foundation pit is the key to rational design of dewatering scheme,and determining the radius of influence of precipitation is the key to calculate the water inflow of foundation pit.In specification,the influence radius of precipitation is calculated according to the empirical formula which sometimes makes big calculation result error.In the case of hydrogeological conditions,the seepage field of foundation pit can be simplified to the solution of Laplace equation.The finite element method can accurately calculate the seepage field of foundation pit,However,due to the overflow boundary unknown,cannot be defined before calculation,the calculation precision is affected.Therefore,to solve the overflow boundary is the premise to calculate the parameters of the seepage field of the foundation pit.In this paper,the problem of the seepage field and influence radius of precipitation is studied,the main results are as follows:(1)From the view of energy,a method to determine the overflow point based on the maximum of energy loss rate is proposed.The overflow point which makes the horizontal energy loss rate of seepage field reach the maximum value is identified as the true overflow point.Compared to the previous calculation method,the advantage of this paper include that the physical meaning of this method is clear,no iteration is required,convergence is easy.(2)A finite element calculation Fortran program for calculating the steady flow problem is established.Two-dimensional and three-dimensional model with test solution and analytic solution is calculated by this program,the relative error between the calculated overflow point and the real position is only 1.29%,1.67%,0.98%.Contrast with the overflow point position solved by other methods,the relative error of this algorithm is smaller,this algorithm has higher accuracy.(3)According to the relation between influence radius of dewatering and seepage overflow point,the calculation program of this method can be applied to the calculation of the influence radius of dewatering of foundation excavations.In this paper,the finite element numerical calculation of two foundation excavations examples has been carried out to calculate the influence radius of dewatering.The results of this paper are 37.23 m,10.16 m.And the influence radius of dewatering calculated by empirical formula are44.72 m,32.17 m.The relative errors were 16.72% and 68.42%,the difference of the two relative errors is large.Through analyzing the problems existing in the empirical formula for the influence radius of dewatering theoretically,proposes use the method of this paper to calculate the influence radius of dewatering as the parameter in the calculation of water inflow.