| China’s infrastructure construction is improving day by day.Roads and railways and other technologies continue to be exported abroad.Among them,the high-quality,high-efficiency and high-innovation tunnel construction projects enjoy a worldwide reputation and gradually occupy a leading position on the international stage.With the rapid development of tunnel engineering,it is also faced with the formidable challenges brought by various complex engineering environments,such as high in-situ stress,weak surrounding rock and passing through broken faults.Reasonable and efficient analysis of the stability of tunnel support structure has become the most important to ensure the quality of the project.Therefore,it is of great significance to further study the stability of tunnel surrounding rock and support structure and put forward the quantitative evaluation method to improve the engineering quality.Based on the convergence-constraint theory,the paper presents the constraint effect of the New Austrian method tunnel support structure and the boundary effect of the model in numerical calculation.The Rupturable Lining model(RL)was developed based on FLAC3 D software,and the RL model was analyzed by indoor concrete compressive and flexural strength tests.The Rupturable Cable(RC)model was developed,and the RC model was verified and analyzed by the pull-out test of the indoor bolt.Based on the Milin Tunnel Project of Sichuan-Tibet Railway,numerical calculation and field testing are carried out to verify the reliability of the model.The research results are as follows:(1)By analyzing the constraint effect of support,there is a certain deviation between the conventional two-dimensional numerical model calculation and the actual engineering.By comparing the calculation results of the two-dimensional model and the three-dimensional model,it can be seen that the structural support strength calculated by the two-dimensional model is too large,and the stress release amount of the two-dimensional numerical model should increase the virtual support force generated by the support constraint effect during calculation,and its value range is 3% ～ 5% of the initial stress.(2)The RL model of rupture type concrete lining and RC model of rupture type anchor bolt were compared with laboratory tests of concrete flexural strength,concrete compressive strength and anchor bolt pulling.The results show that the failure characteristics of the numerical model are basically the same as those of the laboratory test,and the stress curve trends are similar.RL model and RC model preserve the mechanical transfer mechanism of Liner element and Cable element,and can characterize the stress and failure characteristics of structural support structure,which are more suitable for engineering stability analysis.(3)The internal stress of concrete lining in Meilin Tunnel engineering site is monitored.By comparing the monitoring results with the numerical calculation results,it can be seen that the boundary effect of the 3D numerical model is close to 1.5 times the tunnel span.The calculation results considering the boundary effect are more consistent with the actual situation of the project,and the cracking support element can reflect the stress characteristics of the concrete lining in the actual project,and can provide support for the quantitative evaluation of the stability of the tunnel engineering. |
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