Simulation Method Of Drainage Hole Curtain And Numerical Calculation Of Seepage Field In Underground Cavern

At present,with the increasing scale of hydropower stations and the increasing complexity of geological conditions,new challenges have been placed on the construction of underground caverns.The statistical results show that the surrounding rock stability,slope deformation and large flow of water in the foundation pit of underground cavern are directly related to the leakage of the engineering area.The drainage hole is the most common seepage control and drainage measure in the underground cavern.How to simulate the drainage hole curtain is extremely critical for accurately evaluating the seepage control effect of the dam foundation and surrounding rock of underground powerhouse.The one dimensional(1D)finite-element method(FEM)line element is proposed to simulate the drainage hole curtain,and the seepage field of the underground cavern with different drainage hole aperture and spacing is compared and analyzed.The influence radius of the underground cavern is obtained using the calculation formula of the influence radius of the foundation pit so as to determine the numerical model range of underground cavern seepage analysis,which provides a new method for the determination of model range.The above method is applied to the three-dimensional seepage numerical model of Ludila Hydropower Station to evaluate the performance of its seepage control and drainage system.The main results are as follows:(1)The accuracy and effectiveness of the 1D FEM line element method for simulating the drainage hole curtain was verified by the well flow formula.A homogeneous three-dimensional model is used as a case with the simplified simulation method for drainage hole,and the seepage flow of the drainage hole is calculated,with the error of 0.16%compared with the result of the well flow formula.The result meets the engineering requirements.Applying the 1D FEM line element method for simulating the drainage hole curtain to practical engineering has both certain accuracy and improved modeling and computational efficiency.(2)An ideal three-dimensional isotropic rock mass is taken as an example to study the effects of different drainage hole apertures and spacings on the seepage field.When the drainage hole aperture is constant,the larger the spacing between the drainage holes,the greater the error between the numerical calculation of the seepage flow and the calculation formula of the well flow formula.When the spacing between the drainage holes is constant,the larger the drainage aperture,the error between the numerical calculation of the seepage flow and the well flow formula is also larger,and the error is all less than 10%.This method can be used when the the drainage hole spacing is 3 m to 6 m and the aperture is 50 to 110 mm of the underground powerhouse,the main transformer hole and the main auxiliary caverns.(3)According to the calculation formula of the influence radius of the foundation pit,the calculation method of the influence radius of the underground cavern under different boundary conditions is established.The three-dimensional finite element model of the homogeneous rock mass is established and the corresponding boundary is applied.The corresponding influence radius calculation formula is selected according to the boundary conditions for verification.The large well method is used to approximate the underground cavern and the surrounding drainage hole curtain as a large well centered on the underground cavern,and the influence radius is calculated.The calculation result is basically consistent with the numerical calculation result.At this time,the seepage flow is less affected by the model range,and the calculation of the seepage is more reasonable.(4)The three-dimensional seepage finite element model of the Ludila hydropower station is established,and the reason for the excessive seepage flow in the dam foundation of the Ludila hydropower station is analyzed.Through the comparison between the actual seepage flow of the dam foundation and the calculated seepage flow under various working conditions,it is found that the main reason for the excessive seepage flow in the gallery of Section 13,the left part below Section 0+103.25 and the left barricade of bucket is the failure of upstream left-bank impervious curtains.In addition,the failure of the upstream riverbed impervious curtain also has an influence on the seepage flow of the dam foundation.The above analysis provides a direction for the improvement of dam foundation seepage control and drainage measures.