Study On The Seepage And The Stability Of Rock Bank Slope With Three-dimensional Fracture Newtwork Under Fluctuating Water Level Of Reservoir

In general,the following reasons such as operation of reservoir,the peak of reservoir water in rainy season,the swell causes by a landslide and dam break have become the major factors that affect the water level fluctuation of reservoir.Under the influence of water level fluctuation of reservoir,the bank slope will produce dynamic and static water pressure,the stress state of the bank slope will change,and the strength of rock mass of bank slope will be reduced too.Eventually the bank slope failures.At present,there is no accepted way to consider the hydrodynamic and hydrostatic pressure field caused by the water level fluctuation of reservoir in the evaluation of bank slope stability.The premise of ascertaining the influence law and characteristics of water level on bank slope is to study the seepage characteristics of reservoir water under the condition of the water level change.However,there is still a lack of practical means and tools for calculating the seepage model of three-dimensional fracture network.Therefore,the effect of fissure water seepage in the evaluation method for bank slope stability is difficult to take into account.The purpose of this paper is to establish a numerical model of discontinuous medium with three-dimensional,which can be used in engineering practice to analyze seepage field and stability of fractured rock bank slope under water level fluctuating.Firstly,only the seepage law of rough undulating single fracture is taking into account to modify the cubic formula,the equivalent width of rough fracture is obtained.And it is a basic parameter for calculating seepage flow in three-dimensional fracture network.Then a geometric model of three-dimensional fracture is established by Monte Carlo method,and the model is reasonably simplified in order to achieve rapid mesh generation.Afterwards,the steady flow numerical solution and the unsteady flow numerical solution of the three-dimensional fracture network seepage model are obtained by using the finite difference method and the finite volume method.Then,the seepage field of rock bank slope with fractured network is calculated by this method under the condition of water level fluctuation,and the saturation line equation is established to derive the hydrodynamic and hydrostatic pressure field generated by seepage process.Finally,the hydrodynamic pressure and hydrostatic pressure fields are superimposed into the mechanical calculation to obtain the deformation and stress fields of the bank slope.Basic on the above achievements,the angle line of the stable bank slope is modified,and a set of easy-to-use rock bank slope stability evaluation method is established under the condition of water level fluctuation.The main contents and achievements of this paper are as follows:(1)The computational fluid dynamics(CFD)method was used to study the flow law of rough undulating single fracture water with different roughness,fracture width,hydraulic gradient and fracture length.According to the principle of equal flow and cubic formula,the mathematical expression of equivalent gap width is established as follows:a_e=0.28a-0.12JRC-6.4I+2.3This formula provides basic parameter for calculating seepage flow in three-dimensional fracture network.(2)The results of water-rock interaction test show that the roughness of limestone surface changes little under the action of water-rock interaction and the strength of fissure wall decreases gradually with the increase of wet and dry cycles,and finally tends to be stable.In terms of Barton's formula,a formula for predicting the attenuation value of the comprehensive internal friction angle of fissure wall under the condition of long-term fluctuation of reservoir water level is cstablished as follows:??=-lg(?)JRCThe water and rock tests show that the reduction of the comprehensive internal friction angle of limestone fissure wall is 1.3 degree under 150 fluctuations of reservoir water level(3)In order to solve the problem that there is no mature numerical calculation method for seepage flow in three-dimensional fracture network,a numerical simulation method is developed independently in this paper.Firstly,a stochastic three-dimensional fracture network seepage model is established.Then,the finite difference method and the finite volume method are used to solve the seepage problem.Finally,a set of practical calculation methods are established for the planar steady seepage and unsteady seepage in the three-dimensional fracture network.(4)Based on the numerical calculation model of steady and unsteady seepage flow in three-dimensional fracture network,more than 150 Rock Bank seepage flows in three-dimensional fracture network are established under the conditions of fracture width,fracture occurrence,fluctuation range of reservoir water level,fluctuation velocity of reservoir water level,slope angle,spacing of structural planes and permeability of structural planes.Based on the model,the effects of different factors on the seepage field and the characteristics of the saturation line of rock bank slope under the fluctuation of reservoir water level are obtained.Then,a variety of correlation analysis methods are using to analyze the influencing factors of saturation line of rock bank slope under water level fluctuation.The fluctuation velocity and fluctuation range of reservoir water level,fissure width are the main factors and the dip angle of rock strata,the spacing of structural planes are the secondary influencing factors affecting the saturation line of rock bank slope under the condition of water level fluctuation.Based on the above five factors,the mathematical expression of bank slope saturation line is established under the condition of water level fluctuation.(5)Based on the saturation line of bank slope under the condition of water level fluctuation,the formulas for calculating hydrodynamic and hydrostatic pressures under the action of groundwater seepage are derived,and the mathematical expressions of tangential forces on rough undulating fissure walls are obtained based on the theory of computational fluid dynamics as follows:?_e=0.0074b+0.0142JRC+60.4486I-0.1859(6)Through the research of this paper,a method to determine the slope angle of bank slope stability based on the seepage principle of three-dimensional fissure network under the dynamic and static water pressure caused by the water level fluctuation is established.Based on stress condition,the mathematical expression of slope stability angle reduction under seepage action is obtained as follows:??=6.884h_k-0.0485?+8.0953I+0.8At the same time,based on deformation condition,the mathematical expression of width(B)of instability zone of bank slope is obtained as follows:B=-0.004?~2+0.222?+0.017?+0.054F+3.466I-0.441L-1.1The method established by this paper is successfully applied to the stability evaluation of the bank slope of the Daning River Bridge on Zhengzhou-Wanzhou Railway.And the results show that the relevant calculation and analysis method provided by this paper is feasible and practical.