| In the underground engineering of hydropower station,groundwater seepage is inevitable,and it is often in dynamic change under various conditions.The traditional steady seepage simulation method is not suitable for this situation,so it is necessary to use unsteady seepage method to simulate the dynamic process of groundwater.Based on the Signorini variational inequality method of unsteady seepage,the equivalent continuum model is used to program,and various problems related to unsteady seepage in underground engineering are discussed in this paper,such as the selection of initial water level boundary conditions of unsteady seepage,the application method of unsteady seepage load,and the unsteady seepage effect of seepage control measures.Finally,the Rumei underground powerhouse is taken as an example By using the above method,the seepage stability in the whole process of construction and operation is analyzed,which provides a certain reference for engineering practice.This paper mainly includes the following aspects:(1)Based on the PVI formulation of unsteady seepage,an improved variable bandwidth iterative method was proposed to solve the variational inequality problem,and a finite element program for unsteady seepage was compiled.Two examples were given to verify the advantages of the improved iterative method and the correctness of the program for unsteady seepage.(2)Based on the standard particle swarm optimization algorithm,the initial seepage water level of groundwater was obtained through inversion analysis,so as to reduce the calculation error of subsequent unsteady seepage.At the same time,a simulation method was proposed when the seepage boundary conditions change during the excavation of underground caverns.The rationality of the results obtained by this method was verified by an example.Based on the above method,the variation law of groundwater during the excavation of tunnels in practical engineering was discussed.(3)According to the deficiency of the existing method of applying seepage load by volume force and buoyancy force,the unstable seepage load in underground engineering was applied to the surrounding rock by considering the initial strain,and its influence on the stability of the surrounding rock around the main cavern during the construction period was discussed.In addition,based on the implicit composite element method of drainage hole simulation,the method was introduced into the calculation of unsteady seepage,and the unsteady seepage parameters of composite element with drainage hole were taken as equivalent values.And a simulation method for the plugging failure process of drainage holes during operation was proposed.Considering the variation of seepage field under different failure degrees of drainage measures,combined with the unsteady seepage program,the rationality of the proposed method was verified by two examples,and the time for the seepage field to reach the most dangerous state after the failure of drainage measures was calculated and predicted.(4)Based on the above method,the whole process of seepage field numerical simulation was carried out on the seepage field of the underground caverns of Rumei Hydropower Station during the excavation and operation period after the anti-seepage measures took effect,and the distribution of the seepage field after the failure of drainage measures to different degrees was analyzed.The stability of the surrounding rock of the cavern was analyzed by threedimensional elastoplastic damage finite element,and the changes in the surrounding rock failure area and displacement of the underground cavern under the unsteady seepage load of excavation with and without drainage measures were considered to analyze the influence of seepage load and seepage control measures on the stability of cavern surrounding rock. |
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