| Since China’s vigorous development of the western region,a large number of water conservancy and hydropower projects have emerged in the western part of China,especially in the southwest,which has promoted the vigorous development of underground engineering.However,due to the complicated engineering geological conditions in the southwestern part of China,how to carry out the excavation and construction of safe underground engineering under the condition of complicated geostress conditions,how to make the stability of the surrounding rock of the large-span high-walled wall cavern more objective,A comprehensive understanding has very important practical significance.The engineering geological conditions of the underground powerhouse on the right bank of Wudongde Hydropower Station on the lower reaches of the Jinsha River are complex.The plant is located inside the mountain,and the scale and span of the excavation is huge.It is difficult to construct in many water conservancy and hydropower projects.This paper takes the main workshop of the underground powerhouse of Wudongde Right Bank(main building excavation rule 333.00m×30.50m×89.80 m,which is a typical gate hole type)as an example.The numerical simulation method based on FLAC3 D method is adopted for Wudongde Hydropower Station.The deformation characteristics and overall stability evaluation of the main building on the right bank have obtained the following research results:(1)Analysis of stability factors of surrounding rock in the right bank of Wudongde Hydropower Station: The stability of surrounding rock of the underground cavern on the right bank of Wudongde Hydropower Station is mainly due to the control of the rock mass structure on the surrounding rock deformation of the underground powerhouse,and the fault and other geology.The structure provides boundary conditions for deformation and failure;the surrounding rock deformation and failure caused by rockburst and other ground stresses will not occur during the excavation process,but the deformation of the plant abutment and the side wall will be increased compared with other parts.Other factors(such as blasting,groundwater,etc.)have little effect on the deformation of the surrounding rock of the cavern.(2)Classification of surrounding rock: Through the study of the classification criteria of surrounding rock,the classification of surrounding rock of the cavern was carried out according to the(Code for Water Resources Engineering Geological Survey GB50287-2008).The surrounding rock classification of the cavern is based on five major factors: rock strength,rock integrity,main structural plane(level)state,groundwater state,main structural plane(level)and underground structure axis.The rock categories are divided into II,III,IV,and V,and the II,III,and IV categories are divided into two sub-categories.The results show that the surrounding rock types are Class II and Class III,and a very small amount of Class IV.The area ratio is about 41%,about 58%,and about 1% respectively.Class IV is located in the thin layer between the upstream side wall 9#～10# machine.The angle section is located at the station number YC=1+185～1+207 and the elevation is 841.5-804m).Among them,the top arch II and III accounted for about 55% and 45% respectively,and the upstream side wall II,III and IV accounted for about 13%,83%,and 4%,respectively,and the downstream side walls II and III respectively.About 48%,52%.(3)Study on the stability of the main square block on the right bank: Through the study of the formation mechanism and failure mechanism of the block arch and the side wall of the cavern,the main failure mode of the surrounding rock deformation of the cavern is made(ie,the top arch block falls.Prediction of slip-slip damage and side wall slip dumping damage).At the same time,the stability calculation is carried out on the typical large square block of the main building on the right bank.The stability of the large arch block of the top arch is below 1.2,and the stability of the bulk of the downstream side wall is 2.01 greater than 1.25.The safety value is greater than the upstream side wall..In the case of a safety factor of 1.25,the stochastic joints of the upstream and downstream side walls are large and stable in the case of a combination of random joints and the hollow space of the cavern;the safety factor of the block walls on both sides is greater than 1.25.It is relatively stable;the stability of the random block of the top arch is extremely poor,and it is destroyed immediately after excavation,and it needs to be supported in time.(4)Surrounding rock stress field: This paper uses FLAC3 D finite difference software to establish the generalized model of the underground powerhouse on the right bank of Wudongde Hydropower Station,and simulates the initial stress state of the underground cavern and the stress and strain characteristics of the surrounding rock of the cavern after excavation.After the excavation is completed,the stress field changes obviously.According to the maximum principal stress cloud map and the minimum principal stress cloud map,the surrounding rock stress of the cavern is mainly composed of compressive stress,and the maximum principal stress is concentrated on the arches and bottom corners on both sides of the cavern.The stress value is between-1.3 MPa and-1.5 MPa.The minimum principal stress of the surrounding rock of the cavern is slightly larger at the bottom corner of the side arch and the upper and lower side walls of the cavern,which is about-0.5 MPa,and the minimum principal stress of the side wall and the bottom plate is generally about-1 MPa.(5)Deformation and displacement characteristics of surrounding rock: After the excavation of the cavern,the surrounding rock of the cavern conforms to the general unloading law of the direction of the empty plane.The deformation of the arch of the cavern is larger than that of the floor,and the deformation of the endwalls is from the top.The downward is in a decreasing state,and the deformation is no more than 5cm,generally about 3cm.The unloading action of the side walls on both sides is prominent.After the excavation is completed,the deformation of the top of the wall is the largest,and the deformation of the rear wall is greater than the bottom of the side wall.(6)Plastic zone: From the results of excavation analysis,the plastic zone of the 7# machine section is distributed along the side wall of the large-span high-span wall,and the plastic zone is mainly distributed along the upper and lower side walls and the bottom plate.Destruction,the plastic zone of the side wall has a depth of about 5m,and the plastic deformation depth of the bottom plate is about 3m.(7)Comprehensive evaluation of surrounding rock engineering geological section: At the end of this paper,all chapters are sorted out,and a comprehensive evaluation of the main plant on the right bank is carried out.According to the results of the classification of the surrounding rock of the caverns in Chapter 3,the surrounding rock of the cavern is mainly composed of II and III,and a very small number of parts are Class IV.On this basis,the stability evaluation of the surrounding rock stability of the main building on the right bank was carried out,and the surrounding rock of the main building cavern of the right bank was further subdivided into five types of surrounding rock such as II1,II2,III1,III2 and IV,and the right bank was completed.Sectional geological evaluation table for the top arch of the plant and the upstream and downstream side walls. |
