Analysis On Rheological Behaviors Of Soft Rock Tunnels During Construction

With the improvement of China's economy and engineering competence,the tunnel projects have gradually extended to the remote areas with complex geology.In ultra-soft rock strata,the surrounding rock of the tunnel is likely to encounter strong rheological effect in the early stage of construction.This effect can cause large deformation of the surrounding rock and lead to problems such as cracking of the secondary lining,shield jamming and so on,which bring great challenges to the safety of tunnels' structure and the efficiency of construction.In this paper,the research is based on a diversion tunnel.The rheological behaviors of the mining and the shield/TBM method tunnel in mudstone and sandstone strata are studied by means of theoretical analysis,laboratory test,data fitting and numerical simulation.The main research contents are listed as follows:(1)Using rock mechanics test system and acoustic emission equipment,the uniaxial,triaxial and uniaxial creep compression tests on mudstone and sandstone samples were conducted.The complete stress-strain curves and graded creep curves of mudstone and sandstone under different confining pressure and different moisture states are obtained.It is found that high confining pressure and saturated state have great influence on the mechanical parameters and failure deformation characteristics of mudstone and sandstone.Under the longterm loads,the mudstone and sandstone both show obvious rheological features.The rheological effect gradually increases with the increase of the stress level.The rheological effect of mudstone is stronger than sandstone.(2)According to the applicable scope and feature description of the classical rheological constitutive models,the Cvisc model is selected to describe the rheological behaviors of mudstone and sandstone.The parameters of the Cvisc model are fitted according to the rheological test data.Based on the fitted creep curves,it can be concluded that the Cvisc model can simulate the rheological properties of mudstone and sandstone samples well.(3)Based on FLAC3 D software,a three-dimensional creep stratum-structure numerical model is established to simulate and analyze the surrounding rock and supporting structure of the mining method tunnel in the construction phase.After the calculation of the model,the influence of the initial support and the secondary lining's construction time on the surrounding rock's deformation and the structure's stress is studied.The principle of the construction time of the initial support and the secondary lining is proposed.Comparing the different rheological behaviors of mudstone and sandstone strata,it is found that the initial support's construction time of the mudstone strata should be earlier than the sandstone strata.As for the secondary lining's construction time,the controlling factor for mudstone strata is the convergence rate of the surrounding rock,and the controlling factor for sandstone strata is the secondary lining's stress.(4)Based on the three-dimensional creep stratum-shield-structure numerical model,the surrounding rock,shield and segments of the shield/TBM method tunnel are modeled.This model simulates the shield jamming accident caused by the surrounding rock's rheological deformation when the shield machine/TBM is stopped.Under the conditions of different shield length and different overcut gap,the friction resistance of the shield,which gradually increases with the increases of stopped time,is calculated.According to the criterion of shield jamming,the shield machine/TBM's jamming time can be predicted.Finally,the comprehensive control measures for preventing the jamming of shield machine/TBM are proposed.