Evaluation Of Rock Mass Quality In Underground Space And Analysis Of Surrounding Rock Stability

With the rapid development of China's nuclear industry,the safe disposal of nuclear waste has become a technical problem.At present,it is recognized that the safest and most feasible disposal method is the deep burial of high-level radioactive waste.However,most of the deep underground space has the characteristics of complex layout,large scale and deep burial.Therefore,in order to ensure the safety of the cavern in design and construction,people should make a scientific and reasonable evaluation on the quality of surrounding rock and on the other hand,reasonably analyze the stability of surrounding rock under different conditions.On the basis of previous studies,this paper analyzes the rock mass classification and surrounding rock stability by taking the tunnel of an underground laboratory for geological disposal of high-level radioactive nuclear waste as the research object.The specific research contents and conclusions are as follows:(1)Making accurate evaluation of surrounding rock quality is an important prerequisite for the design and construction of the tunnel excavation.The extension cloud model can reflect the fuzziness and randomness of the evaluation standard interval and can give consideration to the qualitative and quantitative analysis of the evaluation indexes.The game theory combines the improved analytic hierarchy process and the improved entropy weight method to determine the combined weight of this paper.Therefore,this paper adopts the extension cloud model based on combined weight to make rock mass quality evaluation of the surrounding rock of the underground laboratory tunnel,the evaluation result shows that the majority of the surrounding rock of the underground laboratory tunnel is with grade II surrounding rocks,while minority with grade IV surrounding rocks.(2)The rock mass mechanical parameters are determined according to the rock mass quality evaluation results and Hoek-Brown criterion.The finite element method is adopted to simulate the influence of the tunnel excavation on the stability of the surrounding rock with different surrounding rock grades(grade ?,?,?).The simulation results show that the grade ? surrounding rock and the grade ? surrounding rock are stable.For the instability of grade ? surrounding rock,this paper introduces the primary support for surrounding rock of the tunnel and analyzes the influence of the primary support on the surrounding rock.On the other hand,the spacing of the tunnel and the direction of the axis are reasonable determination in the simulation,the results show that it is more favorable when the angle between the axis direction of the main tunnel and the maximum horizontal principal stress direction is 0 ? 30 °and the spacing of main tunnels is about 20 m.(3)The representative discontinuity near the roadway is selected,and the extended finite element method is used to simulate the influence of tunnel excavation on the surrounding rocks and the expansion of the discontinuity under the conditions of different surrounding rock grades,different discontinuity positions,different discontinuity inclinations,different crack lengths and different internal friction angles.The simulation results show that the extension length of the discontinuity and the displacement of surrounding rock will increase with the increase of the surrounding rock grade,and the extension direction of the discontinuity is almost perpendicular to the direction of the maximum principal stress;Among the discontinuity at different positions(arch bottom,arch waist and arch vault),the influence on the stability of the surrounding rock is most unfavorable when the discontinuity is located at the arch waist;The inclination of discontinuity is an important factor affecting the stability of the surrounding rock.Among the different inclinations of discontinuity(65°,75°,85°),the discontinuity with inclination of 65° is most unfavorable to the stability of the surrounding rock.The influence of the size of the crack on the stability of the surrounding rock is bounded.When the width of the crack is the same,the length of the crack is between 4m and 8m,the stability of the surrounding rock will become more unfavorable with the increase of the length of the crack,when the length of the crack is more than 8m,the influence of the length of the crack on the surrounding rock will be basically kept stable;As the surrounding rock considered in this paper is of good quality,the internal friction angles(27°,37°,47°)of different discontinuities have little influence on the surrounding rock.The conclusions and rules obtained above have certain reference value for the design and construction of underground laboratory tunnels.