Non-uniform Frost Heave Characteristics And Deformation Law Analysis Of Rocks Surrounding Cold-Region Tunnels

Compared with general tunnel engineering,cold-region tunnels are prone to a series of diseases,such as frost heave cracking,crushing,peeling,ice hanging,watering of ballast bed,frost heave at bottom and water leakage and ice hanging at vault top.Frost damage is one of the main factors to affect the stability of cold-regional tunnels.The influence of accurate evaluation of frost heave on tunnel safety plays an important role in construction technology and measures to prevent frost damage of cold-regional tunnels.The surrounding rocks of tunnels prone to frost heave in cold regions are mainly alluvial deposit or gravel soil with poor self-stabilization ability.Hence,alluvial deposit which is easy to frost heaving is taken as the research object in this paper.The frost heave characteristics and deformation law of rocks surrounding cold-region tunnels are studied through indoor frozen soil mechanical experiments,combined with numerical simulation and theoretical analysis.(1)The freezing process of rocks surrounding cold-region tunnels is uni-directional along the radius.The frost heave variation of surrounding rock under unidirectional frozen conditions and different boundary loads is studied under steady stress condition by using a self-developed test device with flexible loading of airbag.The ratio of frost heave strain in temperature gradient direction to frost heave strain perpendicular to temperature gradient direction is defined as non-uniform frost heave coefficient.The non-uniform frost heaving coefficients of test samples under different conditions provide experimental basis for accurately establishing the constitutive relationship of frozen surrounding rock and considering the value of non-uniform frost heaving coefficients in analytical calculation of surrounding rock.The test results show that the soil samples exhibit non-uniform frost heave characteristics.The frozen strain in all directions can be divided into cooling shrinkage stage,frost heave growth stage and stable stage.The temperature change of samples can be divided into rapid cooling process,slow cooling process and constant temperature process.With the decrease of temperature and stress difference,the coefficient of non-uniform frost heave increases gradually.Quantitative relationship between non-uniform frost heave coefficient and temperature and stress difference is clarified by data fitting.(2)Uniaxial acoustic emission(AE)and triaxial shear tests are carried out at different temperatures(-4?,-8?,-12?,-16?).The results show that the strength and modulus of elasticity of frozen soil increase linearly with the decrease of temperature.In the triaxial test,the shear strength decreases with the increase of confining pressure at-4? and-8?,and the average reduction rates are 0.138 and 0.056,respectively.The triaxial shear strength increases gradually with the increase of confining pressure at-12? and-16??and the average growth rates are 0.233 and 0.417,respectively.The relationship between temperature and internal friction angle,temperature and cohesion is given by using exponential function fitting method.Mohr-Coulomb yield criterion considering different negative temperatures is established.(3)The deficiencies of constitutive equation of frozen surrounding rock are improved considering non-uniform frost heave.The mechanical calculation model of tunnel in cold region is established for the effect of temperature on frozen surrounding rock.The method for solving the coefficient of non-uniform frost heave is given.Combined with FLAC3D,the temperature field of tunnel in cold region is simulated and analyzed to determine the radius of temperature circle divided by frozen surrounding rock.Three cases are solved and analyzed according to the location of plastic zone of frozen surrounding rock.The stress field and displacement field distribution of rocks surrounding cold-region tunnels can be obtained.The development law of plastic radius and stress at each interface under uniform frost heave and uneven frost heave conditions are compared and analyzed.