Study On Stability Evaluation Of Surrounding Rock Of Hydraulic Tunnel Based On Extension Cloud Model

The uneven distribution of water resources has long been a huge obstacle to the economic development of our country.In recent years,China has built a series of large-scale cross-basin water conservancy projects,such as the middle route of the South-to-North Water Diversion Project,to meet the development needs,which has greatly improved the water shortage in the northern region.As the main hydraulic structures of these cross-basin large-scale water conservancy projects,hydraulic tunnel gradually presents the characteristics of large tunnel diameter,high buried depth and long tunnel line,which also becomes a challenge to maintain the stability of hydraulic tunnel.Hydraulic tunnel’s stability bases on surrounding rock stability.If surrounding rock stability can be veracious calculated,it canactively guide tunnel construction and support scheme design in latter work.By this way can greatly reduce risk during construction and make hydraulic tunnel project the safety and stable.However,the research in this field is still in the period of continuous improvement,so it is necessary to increase the research in this field,improve its evaluation system,and make the prediction results more reliable.This paper is to evaluate hydraulic tunnel surrounding rock stability before construction,research the influence of various mechanism of hydraulic tunnel surrounding rock stability,builds theindex system which bases on multi-factor to estimate hydraulic tunnel surrounding rock stability,divides the level of surrounding rock according to stability,bases on the nonlinear theory of extensible cloud evaluation modelto research the hydraulic tunnel surrounding rock stability and analyzes the evaluation results’ effectiveness of surrounding rock stability.It can provides a new quantitative method to calculate the stability of hydraulic tunnel surrounding rock by this paper.Through the study of this paper,we hope to further improve the evaluation system of surrounding rock of hydraulic tunnel,and provide a more effective explanation for the stability evaluation results of surrounding rock of hydraulic tunnel in subsequent projects.In this way,the risk is estimated in advance,and the special support scheme and excavation scheme are done to ensure the safe development of the project.The main contents and research results of this paper are as follows:(1)Establishing the stability evaluation index system of surrounding rock of hydraulic tunnel.After summarizing the existing relevant research data,establishing an index system bases onthe core elements which includesurrounding rock mass characteristics and geological environment.The primary indexes are divided into rock mass quality,rock mass integrity and other factors.The secondary indexes include 10 indexes,such as rock mass quality index,wet compressive strength,integrity coefficient and groundwater seepage etc.Refer to the relevant specification for hydraulic tunnel surrounding rock class hierarchies,performance stability of surrounding rock in the form of surrounding rock grade(grade of surrounding rock is divided into five grades,Ⅰ for stability,Ⅱ is basically stable,Ⅲ for local stability,Ⅳ is unstable,Ⅴunstable).(2)Establishing the stability evaluation model of surrounding rock of hydraulic tunnel based on extension cloud theory.Through the analysis and comparison of various weighting methods,the combined weighting method of "order relation method-improved rough set-game theory method" is established for weighting each index.The cloud model is used to improve the inadequacy that the extension matter element model can only qualitatively express the characteristics of things.Based on this,the extension cloud evaluation model for the stability of surrounding rock of hydraulic tunnel is proposed.Finally,the Matlab software is used to complete the calculation of the extension cloud evaluation model.(3)Based on the water resources allocation project of the Pearl River Delta to start study.Make the bid B4 hydraulic tunnel surrounding rock of this construction as the research object to study grade prediction,the prediction results for GS20+050～GS21+340、GS26+035～GS26+900 section of surrounding rock in Ⅱ level basically stable state,the mileage range for GS19+590～GS20+050、GS21+340～GS22+226 and other mileage range surrounding rock in level III local stable state.The excavation and support scheme are designed according to the predicted results.(4)Using Midas software to simulate construction analysis to determine the reliability of the evaluation results.With the help of MIDAS software,the modeling of surrounding rock excavation and support scheme of GS20 + 050 ～ GS21 + 340 section of tunnel is simulated and analyzed.The displacement and stress changes of rock mass under the condition of excavation and support are taken as the indexes of surrounding rock stability analysis.The reliability of the evaluation model for surrounding rock stability of extension cloud hydraulic tunnel is verified by the analysis results.