Research On The Time-space Effect And The Reasonable Supporting Time Of The Bias Soft Rock Tunnel During Excavation

With the rapid development of traffic construction in our country,tunnel construction and underground engineering is increasing In soft rock area. Because rheological is an important mechanics characteristic of the soft rock,large deformation in soft rock tunnels always has close relationship with the rheological characteristic.At present,In tunnel design the elastic-plastic constitutive model is often adopted to describe surrounding rock,however,the soft rock tunnels have obviously rheological properties In fact. So considering the rheological properties of soft rock has the vital significance for tunnel support problems. This paper relies on the peach-nek-tunnel engineering In Chongqing,disguises the large deformation disaster in the tunnel construction process by the method of combining site monitoring, the indoor experiment and numerical simulation,and researched the construction mechanic characteristics of this tunnel,the reasonable time for the primary support and the second lining and the space constraints effect of tunnel excavation face considering time effect. The research work and results are as follows:①Research the domestic and foreign material of soft rock creep properties,summarized soft rock creep test and the affecting factors of tunnel large deformation disaster,and analyzed the disasters that took place during the peach-nek-tunnel construction.②Drilled rock sample from the peach-nek-tunnel construction site,do indoor rock uniaxial compression test, thus obtained the stress-strain curve. Based on the uniaxial creep test under five loading levels conditions,produced the uniaxial strain– time curve under different loading levels,and analyzed the changing rule of the creep curves with different stress levels of loading. According to creep curve characteristics to choose the creep constitutive model,and adopted Origin7.0 software to fit the creep parameters.③According to peach-nek-tunnel site condition established calculate model, used elastic-plastic constitutive model and creep constitutive model to simulated and analyze respectively, combined site monitoring results contrast to contrast,chose the constitutive model that can describe deformation characteristics of surrounding rock mass from the site closely. Use FLAC^3D software as an analytical tool to analyze and discuss the reasonable supporting opportunity of primary support and secondary lining for soft rock tunnels that have creep characteristics. ④Use FLAC^3D software as an analytical tool to establish the 3D model of peach-nek-tunnel, and simulated the mechanical behavior of the tunnel surrounding rock and support structure during construction period, and select a typical cross section of the surrounding space to analyze the excavation surface effects and time effects, discusses the space constraints effect of excavation face .