Boundary value of high hydraulic pressure upon segment lining in railway tunnels

Railway tunnels mostly under complicated geological environment of mountains or rivers have been threatened with groundwater. So far there has been no clear boundary value of water level in the field of tunnel engineering. In response to the characteristics of lining structure, both aspects of joint water-proof and lining bearing capacity are studied. A decision method about press loading capability of lining structure is put forward, with different design parameters of surrounding rock level, concrete grade and thickness of lining. Large-scale similar model tests are performed to study the mechanical characteristics under water pressure. The study shows that according to the technical requirement of joint open and dislocation, taking into account stress relaxation and aging of the materials, the designed capacity for water pressure of sealing gasket is about 0.8~1.0 MPa. The waveform of structural safety coefficients at different positions of segment lining resembles a sine curve, and the crown and bottom of the tunnel are load control points. The boundary value of high hydraulic pressure can be obviously increased by improving concrete grade and thickness of lining. The failure mode of segment lining under high water pressure is owing to compression , on the contrary, it is due to tension. The axial force is improved significantly and the bending moment is little changed with the increase of water pressure in certain range, which is favorable to lining structure.