Loosening Pressure Evaluation Of Surrounding Rock And Stability Analysis For Tunnel

Tunnels have become an important part of the road because of varied topography and complex geological conditions of China.The tunnel loosening pressure is one of the main form pressure that apply on the support system of tunnel. It has a major impact on the tunnel support system design, construction and post-operation. In order to make a better analysis on the stability for the tunnel, the pressure will be the research object in this thesis, and the existing analysis methods of loosening pressure would compare to each other and be analyzed.The main tasks of this thesis are as follows:Firstly, the common calculation methods of loosening pressure were described in detail and classified according to its background. The factors which affect its applicability also were simply analyzed and summarized for subsequent research and improvement of calculation methods.Secondly, calculation methods for loosening pressure of tunnel surrounding rock based on the RMR system were researched. The missing and inadequate of consideration were understood by comparing original RMR rock classification method and other method. In order to achieve a reasonable improvement on RMR classification methods, the factor which should be considered would be reasonably introduced, and the shortage of the method itself was compensated basing on comparative analysis results of the two classifications. The research subject was a mountain tunnel in western Hunan. The ultimate bearing capacity of supporting system was got according to parameters of the engineering, and the load of support system was determined basing on RMR scores. Tunnel stability was analyzed in combination with two parts. The effect of modified RMR classification was examined refering to the practical stability situation of the tunnel.Then, FLAC3 D, a numerical simulation software, was used to build the tunnel analysis model. And the rock parameters ware obtained according to the scores of RMR classification that before and after modified. The effect of modified RMR classification was verified according to three the relation between allowable limit displacement and the displacement of monitoring points around the tunnel, and the change of the plastic zone of tunnel models that before and after modified. The effect on stability of tunnel by adjust the height-span ratio was discussed.Finally, data of tunnel which occurred arched collapse collected from literature. Analysis of the relationship between calculation height, loosening pressure computing required, and collapse practical height. The distributions of calculation height and collapse practical height were summarized through the span, height-span ratio and surrounding rock quality of tunnel. The impact of the different types weak layer during tunnel excavation process was analyzed by model tests. Their impacts degree compared according to collapse heights of each tunnel model.