Ideal Point Method Model For Risk Evaluation On Rockburst And Large Deformation Of Mountain Tunnels And Its Application

Rockburst and large deformation disasters frequently occur during the construction of deep lying and long tunnels in complex mountainous areas,and it seriously affects the construction safety,construction period and project cost of tunnel engineering.Therefore,there is an urgent need to accurately evaluate the location and risk level of tunnel rockburst and large deformations,and it has important guiding significance and significant social benefits for the preliminary survey,route selection design and the later construction of tunnel engineering.This paper summarizes and analyzes the failure characteristics and occurrence rules of rockburst and large deformation cases in typical mountain tunnels.By means of theoretical analysis and numerical simulation analysis,combined with on-site geological survey,rock mechanics test and monitoring measurement,and the main influencing factors and effective risk evaluation methods of mountain tunnel rockburst and large deformation disasters were studied.The research mainly achieved the following results:(1)By summarizing the failure characteristics and occurrence rules of rockburst and large deformation in mountain tunnels,the key influencing factors of rockburst and large deformation were studied and analyzed,and constructed a complete evaluation index system for rockburst and large deformation.(2)Combining the analytic hierarchy process and the entropy method,the distance function was introduced to establish a combination weighting rule.This method solves the problem of the difference between a single objective weight or a subjective weight,and makes the determination of the evaluation index weight of rockburst and large deformation more reasonable and reliable.The ideal point method can comprehensively consider a variety of influencing factors to evaluate the risk of rockburst and large deformation,solve the limitation and one-sided problem of a single evaluation index,and improve the accuracy of rockburst and large deformation risk evaluation.(3)Based on the ideal point theory and calculation rules,the Euclidean distance function in the Minkowski distance function was selected,and the ideal point model was applied to the risk assessment of tunnel rockburst and large deformation.The evaluation result was basically consistent with the actual situation of the project.The accuracy rates of rockburst and large deformation reached 93.3%and 90.9%respectively,which verified the accuracy and feasibility of the model.(4)Combining the regional geological data and the measured in-situ stress data,a three-dimensional geological model of a Sichuan-Tibet railway tunnel was established through COMSOL Multiphysics and Rhino,and the initial in-situ stress field inversion analysis was carried out based on the boundary load adjustment method.The maximum horizontal principal stress S_H on the axis of a tunnel on the Sichuan-Tibet railway was7.36～49.87MPa,and 73.0%of the area along the tunnel was in a state of high to extremely high geostress state,with high goestress conditions for rockburst and large deformation.(5)Apply the ideal point model of rockburst and large deformation risk evaluation for a deep lying and long tunnel on the newly built Sichuan-Tibet railway.The total length of the tunnel is 14376.53m,and the total length of the rockburst evaluation section is 3999m,accounting for 27.82%;the total length of the soft rock deformation assessment section is810m,accounting for 5.6%.