Damage Mechanical Characteristics And Constitutive Model Of Jointed Rock Mass Under Freeze-Thaw Environment

Jointed rock mass was a kind of common complex rock mass in practical engineering.Due to the existence of joint surface,the strength and deformation characteristics of rock mass show obvious anisotropy and weakening characteristics.As“14th Five-Year" plan and "One Belt and One Road" strategy was gradually advancing,various geotechnical projects such as transportation,water conservancy and hydropower will extend to the more remote cold areas.The pore water in natural rock mass was frozen,thawed and migrated by freeze-thaw cycle,which accelerates the damage of rock mass and causes great danger and trouble to the construction and operation of geotechnical engineering.Therefore,in order to fully reflect the influence of rock structure characteristics,occurrence environment and load on the damage and deformation characteristics of rock mass,the damage constitutive model of jointed rock mass under normal temperature load and freeze-thaw load was studied in this paper.The main research contents and conclusions are as follows:(1)Considering the influence of joint initial damage and the heterogeneity of rock mass structure,based on D-P criterion,the damage model of jointed rock mass was established,and the theoretical expressions of model parameters are derived.In order to better describe the whole process of deformation and failure of joint rock mass under load,the joint rock mass under load is abstracted as damage and undamage.The damage part includes joint damage,load damage and coupling damage.The damaged part bears residual stress,the damage constitutive model of jointed rock mass reflecting the residual strength stage was established;the coupling effect of joint and load damage and its induced macro mechanical response were theoretically characterized,and the effect of joint condition and strain on damage evolution and deformation and failure characteristics of rock mass is depicted.(2)Considering the influence of joint,freeze-thaw and load factors on rock mass.Firstly,based on the number of damage micro elements,a coupled damage model of rock under freeze-thaw loading was established.Then,the jointed rock mass under freeze-thaw and load was equivalent to the damage of rock mass under two-level loading,the first level was the initial damage caused by prefabricated joints,and the second level is the total damage caused by freeze-thaw and load after prefabricated joints.The multi factor total damage evolution equation and constitutive model of jointed rock mass under freeze-thaw load were established.(3)The complete red sandstone samples were cut and 0° and 45° dip angle;The mechanical properties and damage value of rock mass under different joint conditions and freeze-thaw cycles were studied by saturated freeze-thaw cycles and mechanical properties tests.The results show that under the same freeze-thaw times,the strength and elastic modulus of rock samples are in the order of intact rock,0° and 45° joint rock mass decreases in turn,and the corresponding total damage value shows the opposite change law;With the increase of freeze-thaw times,the macroscopic mechanical characteristics of red sandstone samples with three joint surfaces show a decreasing trend,and the corresponding total damage value increases gradually.(4)Based on the characteristics of total stress-strain curve and deformation mechanism of jointed rock mass,the jointed rock mass under freeze-thaw loading was abstracted into damaged and undamaged parts.The damaged part includes joint initial damage,freeze-thaw damage,loaded damage,joint and freeze-thaw coupling damage,joint and load coupling damage,freeze-thaw and load coupling damage and three coupling damage,the freeze-thaw damage constitutive model of jointed rock mass reflecting the residual strength stage was established.The results show that the model can more directly reflect the post peak residual strength stage of rock mass.