Study On Engineering Geological Characteristics Of The Altered-rock And Stability Of The Abutment Slope On The Right Bank Of Banda Hydropower Station's Middle Site

The stability of the abutment slope is the key to ensure the long-term stability of the dam.The development of the altered rock mass in the abutment slope often constitutes the engineering geological problem of large hydropower projects.A number of altered rock masses that control the stability of the slope have been developed on the right bank abutment slope of the middle dam site of Banda Hydropower Station.The geological defects of such hydropower engineering rock mass can also have a great impact on the stability of the abutment slope after excavation disturbance.The altered rock mass developed in the right bank abutment slope of the middle dam site of Banda Hydropower Station has the characteristics of hole development and water softening.The engineering geological characteristics and spatial distribution characteristics of the altered rock mass in different environments will cause different degrees of deterioration of the stability of the abutment slope and threaten the long-term stability of the dam.Aiming at the engineering geological characteristics of the rock on the right bank abutment slope of the middle dam site of the Minjiang Banda Hydropower Station and its impact on the stability of the slope,this paper has carried out systematic and in-depth research and achieved the following results:(1)From the detailed field investigation and indoor data compilation,the spatial distribution characteristics,macroscopic development characteristics,rock mass structure characteristics and structural surface development characteristics of the abutment slope slope are recognized.The conventional test system analyzes the deformation,strength characteristics and microscopic development characteristics of the altered rock.Based on the above analysis results,the overall model of the study area is generalized for numerical simulation calculation under natural and excavation conditions,and the influence of the altered rock mass on the stability of the abutment slope in two states is compared and analyzed.The long-term stability of the slope was evaluated.The results of the thesis can provide a basis for the long-term stability evaluation of the right bank abutment slope of the middle dam site of Banda Hydropower Station.(2)The study area is located in the highland stress area of Tibet.It belongs to the alpine gorge landform.The valley is deep and the weathering unloading depth is large.It is affected by physicochemical and alteration,the rock mass is broken,the weathering rust is serious,and the overall rock mass quality of the dam shoulder slope Poor,mostly iv grade and iii grade rock mass,and the water in some sections is serious.Due to the strong weathering unloading effect,the slope rock mass structure is poor,mainly developing iii,iv and v-level structural planes,of which iii,iv-level structural planes are relatively developed,and are mostly filled with gravel or secondary mud to form weak structures.The surface constitutes the boundary of the secondary stress field and mainly affects or controls the engineering rock mass.(3)Three alteration zones are developed on the abutment slope of the right bank of the middle site.The altered SB2 is the largest,and the entire right bank abutment slope is cut along the ductile shear zone,which plays a major role in controlling the stability of the abutment slope.The altered SB3 is the smallest,although it develops in the ductile shear zone.Medium,but has little effect on the stability of the slope;the altered body SB4 develops in the ductile shear zone 1 near the valley,although the scale between the SB2 and SB3,but due to the proximity of the river valley,the immersion of water in the normal water storage season,The degree of alteration is relatively large,and the engineering properties of rock mass are poor,which has a certain degree of influence on the stability of slope.(4)According to a number of basic tests,a comprehensive understanding of the engineering geological characteristics of altered rocks has been made.The altered rock is a rock with low water absorption and weak expansion.With the increase of alteration and weathering,the compressive strength and modulus of deformation gradually decrease,and the Poisson's ratio and peak strain gradually increase.The deterioration of the engineering properties of the rock mass is mainly manifested by the decrease of cohesive force.At the same time,the water-rock action of the altered rock is mainly manifested by the decrease of cohesive force and the enhancement of the degree of alteration.(5)Through the analysis and research on the development characteristics,deformation and failure characteristics and instability failure modes of the right abutment slope of the right bank of the dam site,the stability coefficient of the abutment slope under different working conditions is calculated.Overall,the overall stability of the slope is better under natural conditions.Under severe conditions such as heavy rain and earthquakes,localized instability and failure may occur in the fractured loose rock mass at the slope.(6)The stability analysis of the slope under natural and excavation conditions by three-dimensional numerical simulation.The results show that the stability of the slope under natural conditions is better than other conditions.However,in the case of excavation disturbance,the shear failure of the excavation slope and the toe of slope is intensified,and the damage zone is penetrated along the strong unloading interface and the first-level excavation platform.Near the excavation platform is a shearing exit,and the bottom of the excavation is the instability of the potential sliding surface.