| Water is the key factor to cause slope instability.Although there are abundant theoretical research results considering the stability of unsaturated soil slope under rainfall or irrigation conditions,there are few relevant calculation software or programs.At the same time,the influence of change of unit weight above water level on stability is not considered in the calculation of slope stability under the condition of rainfall or irrigation.Therefore,there are still some problems in the calculation process of slope stability coefficient under transient seepage.In this paper,combining the theory of unsaturated seepage and relevant finite element theories,the Smith & Griffiths slope finite element program(S&G program)is modified,and the finite element program of loess slope under transient seepage conditions is compiled,and it can consider suction?changes of unsaturated unit weight and strength changes caused by changes in soil moisture content on slope stability,and the slope stability coefficient calculation function under rainfall or irrigation condition is realized.The main research results of this article are as follows.(1)The finite element program of seepage flow under rainfall or irrigation is written in Fortran language.The parameters needed for calculation are input in the finite element program of seepage flow,and the grid division,soil parameter assignment,initial conditions and boundary conditions will be set automatically.After the calculation,the finite element program of seepage flow outputs the pore water pressure value and the Gauss point pore water pressure correction value at the specified time of each node in the slope;(2)The S&G program is modified to consider the slope stability under the action of unsaturated seepage.Based on the shear strength formula of Vanapalli unsaturated soil,the Gauss point pore water pressure correction term output by the finite element program of seepage flow is superimposed on the normal stress of S&G program,which solves the problem that the original S&G program can't consider the suction in unsaturated region;(3)The influence of the change of soil unit weight on slope stability in unsaturated area is considered.After obtaining the volume moisture content of each Gauss point at the specified time in the finite element program of seepage flow,the unit weight value of each Gauss point can be solved by the unit weight calculation formula.The modified S&G program is used to convert the Gauss point gravity load to the element node,so as to consider the influence of the unit weight change of unsaturated region on the slope stability due to the change of water content;(4)The SEEP/W module and SLOPE/W module of Geostudio software are used to check and calculate the finite element program of loess slope.The results show that the pore water pressure field calculated by SEEP/W module is basically the same as that of the program output,and the stability coefficient calculation results of SLOPE/W module and program are not different,which proves the reliability of the finite element program of loess slope;(5)The influence of difference form,element form and change of unit weight on the finite element program of loess slope is studied.The results show that the middle difference method or backward difference method has no effect on the calculation results of the program;The eight node quadrilateral element is not necessarily more accurate than the four node quadrilateral element,but it will make the convergence difficulty and calculation time longer for the finite element program of seepage flow in this paper;Considering the change of unit weight in the unsaturated region will make the calculation result of the stability coefficient more consistent with the actual situation.Therefore,it is necessary to consider the change of unit weight in the finite element program of loess slope. |
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