PLASTIC SOLUTIONS OF A COLD REGION TUNNEL UNDER FREEZE-THAW CYCLES AND NON-UNIFORM FROST HEAVE

Long-term freeze-thaw cycles of the seasonal cold region result in the deterioration of strength and deformation properties of surrounding rock, which make cold region tunnels easily reach a plastic state, and surrounding rock of a cold region tunnel displays the non-uniform frost heave mainly in radial direction. Based on the Mohr-Coulomb criterion, plastic solutions of the frost heaving force, stress and displacement for a cold region tunnel were presented. The proposed solution reasonably accounts for the deterioration of surrounding rock properties caused by freeze-thaw cycles and the non-uniform frost heave of surrounding rock. Meanwhile, the corresponding elastic solutions and a means to determine the elasto-plastic state of frozen surrounding rock were introduced. Furthermore, discussions and comparative verifications of the proposed solution were performed. Finally, the effects of freezing-thawing cycles, the non-uniform frost heave and volumetric frost heave ratio on stress distribution, plastic zone radius, wall displacement and frost heave force of cold region tunnels were investigated. It is indicated herein that the proposed solution has broad applicability and decent comparability, which is partly demonstrated by a plastic solution available in the reference. With increasing the number of freeze-thaw cycles, the frost heave force, wall displacement and plastic zone radius are increased by 20.3%, 8.44 times, and 2.16 times, respectively. It quantifies the deterioration effect of surrounding rock properties caused by long-term freeze-thaw cycles. When frozen surrounding rock is frost heaved from a uniform model to a non-uniform one, the frost heave force is increased by 42.8%, yet the radius of plastic zone is almost unchanged. Four parameters of volumetric frost heave ratio significantly affect the frost heave force, peculiarly the water-heat migration factor which leads to the increase of the frost heave force by 123.6%. The results of this study can provide some theoretical basis for the design and frost damage solving of seasonal cold region tunnels.