Study On Statistical Methods Of Random Structural Surface Of Rock Mass In The Dam Area Of The Maji Hydropower Station Situated In The Quickly Uplifting Nu River

The proposed double-curved arch dam site of Nujiang Maji Hydropower Station is located in Maji Township,Fugong County,Yunnan Province.It is designed 300 meter high.The station of installed capacity is 4,200 MW and average annual generating capacity is 18.97 ×105 kW,h.The whole area of the dam area is mainly uplift,In the background of quickly uplifting of Qinghai-Xizang Plateau,along with the fast undercutting of river and the transformation of the shallow surface,the rock mass on both sides of the valley is produced deformation failure damage.At the same time,the transformation of stress field also leads to the potential threat of collapse,slip and flow geological disasters,which are closely related to the structural characteristics of rock mass.This paper studies the structural characteristics of the rock mass under the special geological background of the Qinghai-Xizang Plateau,and analyzes the relationship between the rock mass structure and the engineering properties of the rock mass,which is of great significance and scientific value to evaluate the stability of structural rock mass,prevent and control geological disasters.In this paper,the Nujiang Maji hydropower station in Yunnan Province as a item foundation.Under the guidance of "rock mass structure cybernetics ",the structural characteristics of the rock mass in the dam site are analyzed and studied in this paper.Mainly obtained the following conclusions:1.Research on the geological characteristics of discontinuities in rock mass based on field measurement,which is located in Maji hydropower station dam site area,the following conclusions are obtained:(1)The left and right bank discontinuities are characterized by heterogeneous development and uneven distribution.Among them,discontinuities with the middle-shallow dip angles in the left bank are dominant,and the proportion is 60-70%,while the steep dip angles inclination is stable,but less.The right bank is mainly developed discontinuous of two steep dip angles and two middle-shallow dip angles,discontinuous of steep dip angle obvious dominant.(2)In the dam area,steep discontinuities principally trend NE-NEE,however moderate dip principally trend NNE、NE-NEE and uncovered in the left and right bank have a different dip direction;The size of the dip angles of the tilt with the high elevation to the bottom of the reduction,in the profile showed inverted "eight" word graphics;(3)The feature of discontinuities aperture in the dam area is dominated by tightness,accounting for more than 90%,followed by open,medium open,and alone precious few in the >10 mm.(4)Trace length on both sides of discontinuities are 1-3m low continuity dominant,accounting for 70%,followed by <1m,3-10 m,while10-20 m,>20m almost no development;(5)The roughness of discontinuity in the dam area develop with similar distribution: left and right banks of the discontinuities are rough wavy dominant,followed by thicker wavy,straight and straight thicker rough,other grades are not developed;(6)There are similar distribution characteristics of the discontinuous groundwater in the dam site,the proportion of dry and wet is relatively large,followed by the wetting and immersion,the dripping condition is relatively small,occasionally the phenomenon of linear water flow and femoral flow;(7)The discontinuities in the dam area are mainly filled with no fouling,accounting for more than 55%,followed by muddy and brecciated debris,rock veins filling less;(8)Discontinuities with slight fade dominant,moderate fading and high degree of fading followed,on the whole,the right bank of the rock weathered degree and slightly stronger than the left bank rock;2.Based on a large number of discontinuities with middle-shallow dip angles in the dam site investigation.This paper discusses the geological causes of the development of t discontinuities with middle-shallow dip angles in the dam area under the background of the uplift of the Qinghai-Xizang Plateau.It is believed that it is mainly due to the effect of the surface reconstruction.Under the tectonic geological background of the Qinghai-Xizang Plateau,Nu River valley has undergone the superseding process of “fast undercutting-basically stable-fast undercutting-basically stable”.It makes the discontinuities in the slope appear relatively dense and relatively sparse.3.During the three-dimensional discontinuities network modeling,we should first determine the statistical homogeneous area,in order to characterize the geological model discontinuities.In this paper,a method to classify the statistical homogeneous region of rock mass structure is proposed for the first time by using the method of K-S test.The method is not limited by the size of the sample,which solves the problem of small sample in practical engineering.Based on wilcoxon rank sum test,a new method was introduced to establish a evaluation model for division of statistical homogeneity of rock mass structure which consider discontinuity orientation and trace length is proposed.By this method avoids the influence of the direction and size of the discontinuities on the homogeneous region.4.In this paper,we study the problem about the discontinuities of classification.The fuzzy C-means(FCM)method based on density algorithm is proposed to improve the traditional FCM method.This study solves the problem that the traditional fuzzy C algorithm is localized into the optimal solution and the initial clustering center sensitive problem in the process of classifying the discontinuities,Consider other parameters that affect discontinuities to the new method.Compared with this method,the grouping result is more ideal and the convergence rate is faster.5.Based on the idea of probability theory and mathematical statistics,a three-dimensional network model of rock mass discontinuities is constructed.To solve traditional 3D network modeling process problems,respectively,the new algorithm is introduced to the model,the division of homogeneity method,classify the discontinuities method,method of trace length estimation,fitting the disc diameter are correspondingly improved.Compared with the traditional modeling,the new model is more practical,which provides a new way to solve the discontinuity of rock mass engineering.6.Based on the developmental characteristics of the discontinuities in the homogeneous region,a three-dimensional network model is constructed,and the three-dimensional connectivity rate of discontinuities is solved by projection method.Finally,we get the spatial development characteristics of the connectivity rate of the discontinuities with middle-shallow dip angles:(1)In different horizontal depth,the connectivity of discontinuities indicates a trend“the incline surface is large and incline internal value is small”.(2)In adit depth,the dip angle of the ideal cross section of the discontinuous indicates a trend “the incline surface mainly develops gentle dip and incline mainly develops internal steep dip”.