Transversely isotropic frost heave of saturated rock under unidirectional freezing condition and induced frost heaving force in cold region tunnels

A series of freezing experiments has been conducted to investigate the frost heaving property of saturated rock under unidirectional freezing condition. Results show that the frost heave parallel to the freezing direction is considerably larger than that perpendicular to the freezing direction, and the frost heave is isotropic on the plane perpendicular to the freezing direction. Thus, the transversely isotropic frost heaving property of saturated rocks under unidirectional freezing condition is proposed, in which the plane perpendicular to the freezing direction is the plane of transverse isotropy and the line parallel to the freezing direction is the axis of transverse isotropy. In cold region tunnels, the inflow of cold air leads to the unidirectional freezing of the surrounding rock along the radial direction of tunnels. Hence, the frost heave of the surrounding rock is transversely isotropic during the freezing process. The cylindrical surface constituted by the circumferential and axial directions is the surface of transverse isotropy and the line along the radial direction is the axis of transverse isotropy. Furthermore, an analytical solution for frost heaving force in cold region tunnels is derived, in which an anisotropic frost heave coefficient k is used to consider the transversely isotropic frost heave of the surrounding rock. The calculated results of the solution are compared with in situ measured data to prove the reasonability of the solution. Finally, the solution is used to optimize the design of the thermal insulation layer of a cold region tunnel.