Study On Long-Term Deformation Of Diatomite High-Speed Railway Tunnel Foundation Under Creep Effect

As a special rock and soil,diatomite has a strong creep effect,which may adversely affect the safe and smooth operation of the tunnel during the operation period.Before this project,there is no domestic experience related to the construction of large-scale high-speed railway projects in diatom soil layers.Therefore,based on the passage of diatomite in the Feifengshan tunnel of the Hang-Shaotai high-speed railway,this paper comprehensively uses laboratory tests,theoretical analysis,numerical calculation,on-site monitoring and other methods to evaluate the creep characteristics of diatomite and the creep effect of diatomite.The long-term deformation of the tunnel foundation is studied.The main research contents and conclusions are as follows:(1)We performed indoor consolidation creep tests.The creep curves of different water contents,different loads and different types of diatomite were obtained.It was found that the creep characteristics of diatomite samples showed three stages: instantaneous deformation,decay creep and stable creep.The creep characteristics of diatomite are more obvious when the load is larger.When the applied stress is small,the instantaneous deformation is small,and the decay creep stage lasts for a short time.When the applied stress is large,the instantaneous deformation increases,and the duration of the decay creep stage is longer.The creep property of white diatomite is stronger than that of blue diatomite,and the creep property of unsaturated diatomite is stronger than that of saturated diatomite.(2)Analyze the scope of application and description characteristics of the classical creep constitutive model,and use the Burgers model to describe the creep characteristics of diatomite based on the results of the indoor consolidation creep test.The creep parameters were identified by nonlinear regression fitting of the diatomite test creep curve.According to the goodness of fit,the Burgers model and its creep parameters can well simulate the creep properties of diatomite.(3)The finite element difference software FLAC3 D is used to establish the deformation prediction model of the unreinforced base of the tunnel,and the influence of objective uncontrollable factors on the long-term deformation of the diatomite tunnel base is calculated and analyzed,and the following conclusions are obtained:(1)The greaterthe tunnel depthis,the greater the long-term deformation of the tunnel base,also its increasing rate decreases with the increasing depth of the tunnel.(2)The order of basement deformation of different diatomite surrounding rock moisture content is:.(3)The order of basement deformation of different diatomite surrounding rocks is:.(4)The creep of the lying diatomite is the main cause of the deformation of the substrate,and the deformation of the substrate caused by the creep of the lying diatomite accounts for about 90% of the total deformation of the substrate.(4)Based on the creep parameters of the surrounding rock determined by the inversion of the inverted arch deformation data monitored on site,the deformation of the steel pipe pile reinforcement base was predicted,and the subjective controllable factors such as base reinforcement,reinforcement pile length,reinforcement pile diameter,etc.were studied.The influence of the long-term deformation of the diatomite tunnel base,the following conclusions are drawn:(1)The deformation of the diatomite tunnel base caused by soft rock creep mainly occurs in the first 3 years of the tunnel construction,and the first and third years occupy about 100 years.75% and 90% of the cumulative deformation of the substrate.(2)The steel pipe pile base reinforcement scheme can effectively control the base deformation of the diatomite tunnel.Compared with no base reinforcement,the steel pipe pile reinforcement reduces the base deformation by about 70%.(3)The longer the length and the bigger the diameter of the steel pipe pile are,the smaller the long-term deformation of the diatomite tunnel base is.However,when the length and diameter of the pile reach a certain level,continuing to increase the length and diameter of the pile has no obvious gain in controlling the long-term deformation of the base.