Research On Construction Mechanics Characteristics Of Super-long Tunnel With Weak And Broken Surrounding Rock

The construction of super long tunnel with weak and broken surrounding rock faces the challenge of extremely bad geological conditions such as strong karst,high ground stress and high gas.In the construction process of Tongzi tunnel,it passes through the bad geological environment such as soft rock and broken surrounding rock for many times,with slow construction progress and high safety risks.Based on the research background of Tongzi tunnel,combined with the indoor model test and numerical simulation method,this paper studies the construction mechanical characteristics under different construction methods,and compares the construction methods,and obtains the efficient and safe construction method of the study section.The main research contents are as follows:1.Drill core samples at the face of Tongzi tunnel research section,process them into standard test pieces,carry out uniaxial compression test,triaxial compression test and Brazilian split test on rmt-301 rock and concrete mechanical test system,and measure the mechanical parameters of surrounding rock in the research section.2.According to the measured mechanical parameters of surrounding rock,the similarity ratio of 1:60 is used to configure the similar materials that meet the conditions;different water paste ratio is used to prepare the initial support with different strength,and the mechanical parameters are measured to obtain the water paste ratio that meets the test strength requirements.3.Simulate the tunnel excavation under four working methods and six working conditions indoors,analyze the response characteristics of surrounding rock stress and initial support internal force during the excavation process,compare and select the working methods,and analyze the optimal excavation bench length.4.Using FLAC3 D analysis software,establish three-dimensional numerical calculation model,simulate four construction methods and six working conditions of tunnel excavation,analyze the surrounding rock displacement field,surrounding rock stress field and stress characteristics of initial support structure after the completion of tunnel excavation and support,and compare the construction methods.5.Based on the results of indoor model test and numerical simulation,the efficient and safe construction method and the optimal length of excavation bench are obtained.