Research On Deformation Mechanism Of Soft Rock Tunnel Under High Stress And Its Application In Engineering

With the development of China's expressway construction, long tunnels passing through poor engineering geological environment or high stress regions are booming, which brings big challenges to the design and construction of expressway. The biggest difficulty of tunneling in soft rock lies in structure design, excavation technique and maintenance in the operation period, as the rock usually is weak, under high ground stress and with high pressure ratio, which lead to large deformation during a long time, and is still a worldwide technical and theoretical difficulty by far.Taking the Xiakou tunnel of Yiba highway as the background, laboratory tests, rock displacement and structure stress monitoring of the tunnel are performed. More attentions are paid to the large deformation mechanism and the excavation and construction method of the soft rock tunnel under high stress by the inverse theory together with numerical simulation technology comprehensively. The large deformation law and structure stress characteristics of soft rock under high stress are obtained, and a nonlinear creep damage constitutive model is put forward and applied in the long-term stability analysis of the tunnel. Then a new reliable excavation method and supporting strength is determined based on the New Austrian Tunneling Method. The main contents of the dissertation are as follows.(1) Based on the results of the triaxial tests and triaxial creep tests, a new nonlinear creep damage constitutive model that can better describe the large deformation and stress characteristics of soft rock under high stress is put forward.(2) Different excavation methods and support measures of soft rock tunnels under high stress are performed with the elastoplastic finite element method. Considering the difficulty of construction and the project cost, the reasonable excavation methods and support measures for various types of rock mass constructed by the New Austrian Tunneling Method are recommended.(3) In-situ stress tests of the surrounding rock, as well as rock deformation and structure stress monitoring are conducted. The large deformation law and stress characteristics of the soft rock under high stress are obtained by the back analysis. The back analysis results agree well with field monitoring data.(4) Based on the nonlinear creep damage model, the long-term stability analysis of the tunnel with different excavation methods and supporting measures is performed by the nonlinear finite element software ABAQUS. The results show that the surrounding rock and supporting structure are in safety after50years, which demonstrate the reliability and feasibility of the theory and methods put forward in this dissertation.