Study On The Tunnel Floor Heave Mechanism Of Yunding Tunnel Along Shanghai-Chengdu Railway

Recent years have witnessed frequent tunnel floor heave problems that suspend the operation of high-speed railway lines and cry for solutions with the rapid development of high-speed railway in China.Yunding tunnel,deeply buried along the Shanghai-Chengdu Railway,is faced with the problem of tunnel floor heaves which have caused great economic losses.Now the formation mechanism of the floor heaves remains unknown.Therefore,based on the floor heave problems,methods including theoretical analysis,laboratory tests,numerical simulation were adopted in this paper to study the causes,influencing factors and deformation features of the floor heaves in Yunding tunnel.The creep mechanical property of the surrounding rock and the formation mechanism of the floor heaves in Yunding tunnel were concluded in this paper,which can provide theoretical basis for relevant treatment and offer reference for studies of other tunnel floor heaves under similar working conditions.The main research work is summarized as follows:(1)Based on a literature review of tunnel floor heaves,the causes of floor heaves were explored through the analysis of the engineering geological condition of Yunding tunnel and the monitoring data of its floor heaves.(2)Basic physical and mechanical parameters of the mudstone and shaly sand of Yunding tunnel were obtained via laboratory rock tests including unconfined uniaxial compression tests and moisture content determination tests,and creep characteristic curves were achieved through the uniaxial step loading creep test of the muddy siltstone and mudstone.The creep deformation characteristics and failure mechanism of mudstone and shaly sand were obtained through the research and analysis of the creep curves,long-term strength and the creep failure morphology of the rock.Based on the creep tests of mudstone and shaly sand in Yunding tunnel,the creep constitutive relation was identified and the corresponding creep constitutive model was determined.Complete creep curves of the rocks under different stress conditions were obtained through Chen method and then fitted to get creep constitutive parameters such as the viscosity coefficient of the constitutive model of mudstone and shaly sand so as to establish the corresponding constitutive model.(3)The numerical model of Yunding tunnel was set up by virtue of the finite element difference numerical simulation software FLAC3 D.The back analysis of tunnel floor heaves was made according to the Burgers creep model to study the force state and deformation feature of the tunnel structure in different creep periods of the surrounding rock,and then the deformation law of the floor heaves and the development law of the tunnel stress distribution were concluded.Moreover,the impact of different elastic modulus of the surrounding rock,buried depths of the tunnel and lateral pressure coefficients on tunnel floor heaves was also discussed.