Analysis Of Influence Of Overbreak In Railway Tunnel Of Grade ? Surrounding Rock On The Stability Of Surrounding Rock And The Stress Of Supporting Structure

In the exiting tunnels and tunnels under construction,due to such reasons as the complexities of the engineering geological conditions and construction technologies,the phenomenon of overbreak is rather common.During the construction process,the defects of lining quality caused by overbreak are bound to exert impacts on the stability of the surrounding rock and the stress conditions of their supporting structures,and it is necessary to conduct in-depth studies of the degrees of their impacts.Based on the above problems,adopting the method of combining the literature investigations,the analysis of the actual engineering data as well as the numerical simulation,this thesis focuses on the study of the impacts of overbreak on the deformations,stress conditions as well as the stress state of the surrounding rock and the stress conditions of the supporting structures.With the tunnels of the railway passenger lines as the engineering background,it explores the most dangerous locations of the surrounding rock and supporting structures under such conditions as different burial depths,overbreak positions and overbreak volumes so as to provide the future constructions of similar projects with references.The main research outcomes as follows:(1)The phenomenon of overbreak is quite common in various classes of surrounding rock,and a great number of them have surpassed the specified values in the specifications,and the positions of the vaults and the arched shoulders are those that are prone to overbreak.(2)Using the finite element method,research is conducted on the impacts of overbreak in such locations as vaults and arched shoulders.The change regularities of the vault settlements of the surrounding rock,the palm-side extrusion shifts,horizontal convergence,stress distribution of the surrounding rock,tensile damage zones as well as the plastic zones are summarized.The results indicate that the impacts of the vault overbreak on the vault settlements and the palm-side extrusion shifts are enormous,and the arched shoulder overbreak also exert certain impacts on the convergence of the side wall.The impact range of the vault overbreak on the surrounding rock stress is mainly concentrated in the vaults and arched shoulder positions,while the impact range of the arched shoulder overbreak is mainly concentrated in the upper guide arched shoulders and the arch waists.In addition,the impacts of overbreak on the damage zones of the surrounding rock are rather complicated and there exists a problem of stress concentration,thus somewhat increasing the tensile damage zones and plastic zones of the surrounding rock and making the stress state less favorable.When the burial depth is elevated,the impact degrees will be even bigger.(3)Further research is conducted on the impacts of the overbreak in such locations as the vaults and arched shoulders on the stress of the supporting structures.It summarizes the change regularities of the stress of the steel arch frame under the conditions of different overbreak heights and overbreak angles.The results indicate that the overbreak changed the stress conditions of the steel arch frames,resulting in the reduction of the compressive stress of the overbreak zones and the increase in the compressive stress of the both sides of the overbreak zones,and they exert no obvious impacts on the lower guided compressive stress values.With the increase in the overbreak heights,the compressive values of both sides of the overbreak zone will be increased accordingly.With the rises of the overbreak angles,the maximum compressive stress is firstly increased and later decreased.In case of different overbreak heights and angles,the locations of the damages of the steel arched supports also differ.