Research On Construction Mechanics In Tunnel Of Weak Surrounding Rock

As the implementation of infrastructural construction in our country, there will be more tunnel passing through the weak surrounding rock in construction of road. However, the research on construction mechanics in tunnel of weak surrounding rock is too little at present. It leads to a serial unstable failure in tunnel of weak surrounding rock. Especially, the research on time effect of stress state in surrounding rock and supporting structure after hole excavation. So, it's necessary to discuss and do research on the above problems more further.At first, the paper systematically discusses the geological characteristics, instable factor, deformation failure's mechanical mechanism and characteristics, supporting structure's characteristics in tunnel of weak surrounding rock;then adopting the viscoelastic method, analysis the mechanical time effect of construction process in tunnel , and analysis of the impact of second support time & first support thickness on the surrounding rock displacement, stress of first support, stress of second support;at last, combined with specific engineering, adopting 2D viscoelastic method and measured analysis, analysis the surrounding convergence, surrounding rock stress, stress of first support, stress of second support, internal force of steel support, contact pressure between surrounding rock and first support & first support and second support, also compares numerical analysis results with measurement data. The main research work and results are remarked as follows:1) The sequence of the impact of spatial effect on surrounding rock displacement is vault, side wall, hance, and on the stress of first support is exactly the opposite. The sequence of the impact of time effect on surrounding rock displacement and stress of first support is related to whether has done second support. While before doing second support, the sequence of the impact of time effect on surrounding rock displacement is vault, side wall, hance, and on the stress of first support is vault, hance, side wall. While after doing second support, the sequence of the impact of time effect on surrounding rock displacement is vault, hance, side wall , and on the stress of first support is vault, side wall, hance. The sequence of the impact of time effect on stress of second support is vault, hance, side wall.2) The sequence of the impact of second supporting time on surrounding rock displacement is side wall, hance, vault, and on the stress of first support is exactly the opposite. If the second supporting time is within 60 days of after excavating, it can reduce the surrounding rock displacement and stress of first support notablely. If the second supporting time is exceed 60 days of after excavating, the effect of second support impact on surrounding rock displacement and internal force of first support is not notable, especially the second supporting time is exceed 100 days of after excavating, the effect is very little.3) The more thickness of first support, the more small of surrounding rock displacement, stress of first support and stress of second support. In the view of the ratio of reduced surrounding rock displacement, stress of first support and stress of second support due to increasing thickness of first support, the ratio of first support of 20 cm thickness is larger than first support of over 20 cm thickness.4) During the construction of bench method, there is a phenomenon of stress concentration in skewback and basement, and the impact of excavating lower bench on increasing speed of surrounding rock displacement is more notable than others. The step of excavating lower bench is a dangerousest step.5) From the comparing numerical analysis results with measurement data, the two results are close. The compared results showed the validity of the viscoelastic and plane strain model of adopting load release ratio to simulate spatial effect in paper.