A Research On Evaluation Of Rock Mass Quality And Surface Selection On The Dam Foundation Of The Right Bank Of Rumei Hydro-power Station

In recent years,with the development of our society and economy and the increasing attention of environmental protection,hydro-power resources in Southwest China have been vigorously exploited and utilized.The proposed Rumei hydro-power station is one of the highest Earth-rockfill dams in China and even in the world,which is up to 315m.Moreover,the discontinuities of the dam site of the Rumei hydro-power station is very developed and the rock mass structure is very complex.Therefore,it is necessary to find out the structural features of the rock mass of the dam foundation,establishing the classification system of rock mass structure and discontinuities.In addition,it is needed to find out the characteristics of the azimuth and shape of different types of rock mass of the dam foundation,so that we can rationally divide the grade of rock mass quality and correctly extract the physical and mechanical parameters of rock mass and discontinuities,providing geological basis for the selection of dam foundation and the stability evaluation of high slope.On the basis of finding out the engineering-geological conditions of the dam site,a quantitative index for the classification of the zone of weathering and unloading of rock mass of the dam site is established.Meanwhile,a new index named weathering-rebound index?RHI?is put forward to zone the rock mass according to the weathering characteristics.Based on that,the rock mass is divided into 4 types,the strong weathering,weak-positive weathering,weak-negative weathering,and fresh rock mass.Similarly,According to the unloading characteristics of rock mass,which is divided into 4 main types,strong unloading,weak-positive unloading,weak-negative unloading,without unloading.The development characteristics of the 3 and 4-grade discontinuities of the right bank were analyzed.For the former,which is divided into 4 groups according to the orientation.The first group is group NNW,which is the most developed,about 31%of the total;the second group is group SN,accounting for 15%of the total;the third group was NNE,accounting for 23%of the total,and the fourth group is NWW,accounting for the total number.28%.For the later,which is divided into 4 groups according to orientation.The first group is group NW-NWW,which is the most developed,accounting for 69.8%of the total;The second group is group NNE,accounting for4.7%of the total;The third group is group NEE,accounting for 7.9%of the total;and the fourth group is group NWW,accounting for about 17.5%of the total.By using RQD,RBI and RSI,the rock mass structure of the dam site is divided mainly into broken-inlay structure,inlay structure,layered structure and sub-block structure,and the secondarily is clastic loosen structure.The rock mass structure of the dam site is complex so as to the different types of rock mass structures often appear alternately in space.In addition,the rock mass in the strong unloading zone is mainly clastic loosen or broken-inlay structure;for the weak unloading zone is mainly broken-inlay,inlay and thinly embedded structure;for the no unloading zone,which is mainly composed of embedded and block structure.By contrasting them with each other,it is found that the RSI index can better characterize the rock mass structure of different parts of the dam base,and the corresponding relationship between the rock mass structure type and the above indexes is obtained.The uniaxial compression,three-axis and three-axis unloading experiments of granite and Angan rock were carried out,which obtained the deformation parameters and strength parameters of the rock under different experimental schemes.In order to simulate the response of rock in the process of excavation and back-filling,the variation of deformation parameters of rock in the elastic stage,unloading stage and reloading stage is analyzed and compared by unloading experiments.According to the comprehensive classification results of rock mass,combined with the results of the in-situ test and the values of the rock mechanics parameters of the dam foundation in the standard,the proposed values of the shear?breaking?strength parameters of the rock mass at all levels of the dam site are given.The span of IV2-grade rock mass?rock/rock?:f'=0.55⁰.65/c'=0.2⁰.5MPa;The span of IV1-grade rock mass?rock/rock?:f'=0.65⁰.8/c'=0.5⁰.7;III2-grade rock mass is divided into two types according to the different weathering and unloading state,weak-positive unloading rock mass as III_2A,which its span?rock/rock?is f'=0.8¹.05/c'=0.7¹.1MPa;weak-negative unloading rock mass as III_2B,which its span?rock/rock?is f'=1.05¹.15/c'=1.1¹.3MPa.And the III1-grade rock mass mainly corresponds to the fresh,and its span?rock/rock?is f'=1.15¹.25/c'=1.3¹.5 MPa.The quality of rock mass is evaluated by the methods of qualitative classification,BQ classification,RMR classification,HC classification,RMY classification and corresponding improvement and correction methods,and the quality grade of rock mass in different parts of the dam foundation is obtained.After comprehensive classification,it is found that the quality of rock mass classified by the original RMR method is the best,the result is the most optimistic,the two classification results of HC method are the second,and the RMR original method is the most conservative.After comparing the comprehensive classification results with the weathering-unloading characteristics of the rock mass,it is found that the IV-grade rock is mainly located in the strong unloading zone,weak-positive unloading zone,fissures densely developed zone and the extrusion-dislocation belt.The III-grade rock mass is mainly located in the weak-negative weathering and unloading zone,the weak-positive weathering and without unloading zone,the fresh rock mass besides.By summarizing and analyzing the principle and basis of the surface selection of earth-rockfill dam and according to the availability of the rock mass of dam foundation,dividing the rock mass into five types,such as the select rock mass?II-grade?,the medium rock mass?III1,III2-grade?,the poor rock mass?IV1-grade?,the weak rock mass?IV2-grade?,and the inferior rock?V-grade?.So the inferior rock mass should be excavated and removed;the poor and the weak rock mass should not generally be used as the foundation of the dam;the mediums should not commonly be used as the foundation of the high dam and should be treated specially if it is used;the select rock mass can be used directly.Based on the comprehensive classification results of rock mass quality,The proposed value of the available range of the rock masses on the right bank axis is given.On the basis of the above work,combining the requirements of the high earth-rockfill dam to the rock mass,the evaluation of the availability of the rock mass is carried out,and the selection of foundation surface of right bank of the middle dam site is proposed.