Study On Creep Properties And Model Of Sandstone Under Freeze-thaw Environment

In order to study the cold regions engineering deformation characteristics under the action of freeze-thaw cycles and long-term load,the scanning electron microscope tests,conventional triaxial compression tests and triaxial multi-level loading and unloading creep tests under different freeze-thaw cycles were carried out on red sandstone in Shaanxi province.The effects of freeze-thaw cycles on the microstructure,mechanical properties and creep characteristics of red sandstone were studied.A freeze-thaw-damage creep model of red sandstone in freeze-thaw environment was established.The main research is as follows:(1)Freeze-thaw cycles and scanning electron microscope tests were carried out on saturated red sandstone.The influences of freeze-thaw on the longitudinal wave velocity,damage evolution and microstructure of rock were studied.The experimental results show that the wave velocity decreases exponentially with the increasing number of freeze-thaw cycles,while the freeze-thaw damage,average pore size and average pore area increase exponentially.(2)The conventional triaxial compression tests of red sandstone after different freeze-thaw cycles were carried out to study the effects of freeze-thaw cycles and confining pressures on rock mechanical properties and deformation characteristics.The results show that the triaxial compressive strength and elastic modulus of rock decrease exponentially with the increase of freeze-thaw cycles,while the peak strain increases exponentially.The influence of confining pressure on the elastic modulus of rock is related to the number of freeze-thaw.When the number of freeze-thaw is small,the elastic modulus increases linearly with the increase of confining pressure,while when the number of freeze-thaw is large,the elastic modulus increases exponentially.The triaxial compressive strength of rock increases exponentially with the increase of confining pressure.(3)The triaxial multi-level loading and unloading creep tests of red sandstone under different freeze-thaw cycles were carried out on TAW-1000 microcomputer controlled rock triaxial creep testing machine.The effects of freeze-thaw and confining pressure on the creep characteristics of red sandstone were studied.The influence of freeze-thaw cycles and confining pressure on the creep deformation of red sandstone is related to the loading stress level.At low stress level,the total creep strain of rock increases linearly with the increase of freeze-thaw times and confining pressure,while at high stress level,the creep strain increases linearly.The dividing point is the fourth stage loading stress level(70%?c).The steady creep rate of rock is greatly affected by freeze-thaw cycles and confining pressure.The steady creep rate increases exponentially with the increase of freeze-thaw cycles and linearly with the increase of confining pressure.The long-term strength of red sandstone decreases approximately linearly with the increase of freeze-thaw cycles.The long-term strength ratio of rock X is proposed and the long-term strength ratio of red sandstone under different freeze-thaw cycles is calculated.(4)Based on the results of the creep test of red sandstone,a freeze-thaw-damage creep model was established considering the effects of freeze-thaw cycles and creep damage.One-dimensional and three-dimensional creep constitutive equations are derived.The model parameters are obtained and the model curves are fitted.The theoretical data is in good agreement with the experimental data.The influence of freeze-thaw cycles on model parameters was analyzed.