Elastic-Plastic Research On Cold Region Tunnels Considering Transversely Isotropic Frost Heave Based On The Unified Strength Theory

Unique frozen damage in cold region brings many challenges to tunnels’ engineering design and site construction.Also,it threatens the safety of tunnels’ management and operation.The frost heaving force is one of the main causes of frozen damage in cold region tunnels.Moreover,the analysis of cold region tunnels,stress and displacement are the key to calculate frost heaving force.At present,most of the elasto-plastic studies on cold regions tunnels assume that the surrounding rock is isotropic frost heaving,and the Mohr-Coulomb strength criterion is adopted as a yield criterion.In fact,the frost heaving of surrounding rock is asymmetrical,and performs transversely isotropic.The intermediate principal stress exsists and has significant influence.Therefore,based on the unified strength theory,displacement of surrounding rock release,freeze-thaw cycles damage effect and the unfrozen surrounding rock yield are studied respectively in this paper,with consideration of the influence of transversely isotropic frost heave of frozen surrounding rock.Then,the solutions of frozen heave force,stress and displacement in cold region tunnels are set.Meanwhile,the comparison validation and parameter analysis are conducted in the results.The results provide theorical guidance for engineering design of cold regions tunnels.The main research contents and conclusions are as follows:(1)The elastic solutions and the unified plastic solutions in cold region tunnels are presented,accounting for the influences of the displacement release of surrounding rock,the intermediate principal stress and the transverse isotropic frost heave comprehensively.The displacement release of surrounding rock in terms of distance is quantified through the supporting time.The results show that it is more intuitive to quantify the displacement release degree of surrounding rock by using the supporting application time.When supporting is applied earlier,the degree of displacement release of surrounding rock is low and the frost heaving force is large.When supporting is applied later,the displacement of surrounding rock is fully released and the plastic zone developed rapidly.(2)Reasonably accounting for the deterioration of surrounding rock properties caused by freeze-thaw cycles and the transverse isotropy frost heave of surrounding rock,plastic solutions of the frost heaving force,stress and displacement for cold region tunnels are presented by according to the unified strength theory.It is found herein that the freeze-thaw cycles have a significant influence on cold region tunnels,and the deterioration effect of surrounding rock properties caused by long-term freeze-thaw cycles should be paid more attentions to.The good waterproof and drainage capacity and effective insulation measures of tunnels should be ensured.(3)Considering the elastic-plastic property of the unfrozen surrounding rock and the transversely isotropic frost heave property of the frozen surrounding rock,the solutions of frost heave force,stress and displacement of the cold region tunnels under four conditions are derived based on the unified strength theory.The results show that the elastoplastic state of both frozen and unfrozen surrounding rock should be judged,and the suitable mechanical model of in the cold region tunnels should be selected to avoid the calculation error caused by the wrong mechanical model.(4)Utilizing the unified strength theory considering the effect of intermediate principal stress as the yield criterion of surrounding rock can give full play to its potential bearing capacity.The intermediate principal stress parameter grows up.Then,the calculated value of frost heaving force decreases,so is the range of plastic zone.This shows that based on the unified strength theory,the engineering design of cold region tunnels has considerable economic benefits.The frost heaving force is apparently influenced by the transversely isotropic frost heave degree and the volumetric frost heaving strain.So is the plastic zone radius.Therefore,main radial frost heave should be highly considered.