| As a hotspot in the field of geotechnical engineering,slope stability has been widely concerned by scholars at home and abroad.Studies have shown that there are many factors affecting the stability of slopes.The change of groundwater seepage field caused by water storage is an important factor leading to the instability and damage of the slope of water conservancy and hydropower engineering.Banda Hydropower Station is the fourth-level power station for hydropower planning in the upper reaches of the Lancang River(river section in Tibet).It is located on the southeastern edge of the Qinghai-Tibet Plateau and is an alpine valley landform with steep slopes.After the dam is built,the water level will rise by about 160 m,and the groundwater seepage field on the slope will change,which will affect the stability of the slope.Based on the on-site geological survey,combined with the engineering geological conditions of the dam site area,the structural characteristics of the rock mass on the right bank slope of the upper dam site are analyzed in depth.The numerical simulation method is used to study the groundwater seepage in the slope during the impounding process.The variation of the field,and further the use of rigid body limit equilibrium method combined with three-dimensional numerical simulation calculation and analysis of the impact of water storage on slope stability,the specific content and results are as follows:(1)Through the detailed investigation of the flat surface of the study area and the surface structure of the slope surface,the structural surface of the study area is divided into four categories: Class II,Class III,Class IV and Class V.Further analyzing its developmental characteristics,and obtaining the dominant occurrence of various structural planes.(2)According to the results of the footrill earthquake wave test in the study area,the rock mass is divided into weakly weathered upper zone,weakly weathered lower zone and micro-new rock mass according to the degree of weathering;at the same time,statistics on the development of unloading and fissures of the flat and slope are calculated.The rock mass in the study area is divided into strong unloading zone,weak unloading zone and unloading zone;based on the classification of weathering unloading zone,the seismic wave test results are used to calculate the integrity coefficients of rock masses at different depths,and then the rock mass is divided into five categories according to the completeness: complete,relatively complete,relatively broken,broken and extremely broken.(3)According to the exposed conditions of various structural planes in the footrill,the average connection rate of the rock mass structural plane is calculated by window method is 35.8%.It has certain reference value for the calculation of the rock mass strength parameters of the right bank slope on the upper dam site.(4)Through the investigation of the flat and slope structure planes and footrill in the dam site area,the structural characteristics of the rock mass on the right bank slope of the upper dam site are analyzed.And the rock mass structure of the study area is divided into four types: block-integral structure,mosaic-block structure,fragmentation structure and granular structure.(5)According to the rock mass quality classification standard,the bq method is used to evaluate the rock mass quality of the right bank slope of the upper dam site,and the rock mass in the study area is divided into four grades according to the quality grade: Class II,Class III,Class IV and Class V.(6)Based on the borehole water pressure test,the permeability characteristics of the rock mass in the study area were studied.The rock mass on the right bank slope of the upper dam site was classified into micro-permeable,weakly permeable and moderately permeable according to the permeability grade.The distribution law is further analyzed.(7)The numerical simulation method was used to study the variation of seepage field during the water storage process of the slope.The variation of groundwater saturation line and the distribution of pore water pressure under different water storage speeds and different water storage levels were obtained.(8)Based on the analysis of the structural characteristics of the slope rock mass,the possible failure modes of the slope are analyzed,and the potential sliding surfaces of the three sections are obtained.The rigid body limit equilibrium method is used to analyze the slope.The stability of different water storage speeds and different water storage levels is calculated,and the stability coefficients of each section under different working conditions are obtained.It is concluded that the stability of the slope during the impoundment process generally shows the law of decreasing first and then rising.(9)Using the three-dimensional numerical simulation method,the overall stability of the slope before and after water storage is studied.Based on the analysis of the stress field,displacement field and shear strain increment of the slope before and after the impoundment,the slope is stored.The overall stability before and after water was evaluated. |
PDF Full Text Request