Study On Physico-mechanical Properties Of Equivalent Material Experiment And Damage Constitutive Model Of Freezing-thawing Single Jointed Dacite

China is one of the countries with the largest distribution area in the cold regions of the world,and there are many projects in various cold regions,such as Xinjiang Tianshan Highway,Qinghai-Tibet Railway and the Sichuan-Tibet Railway currently under construction.These projects will involve fractured rock masses.The importance of physical and mechanical parameters and constitutive relations to engineering projects is self-evident.In the cold region,the fractured rock mass has experienced many years of freezing and thawing,and it is usually different from the ordinary fractured rock mass in terms of physical and mechanical properties and constitutive equations.Therefore,the study of the physical and mechanical properties and constitutive relationship of the frozen-thawed fractured rock mass is very necessity.Taking the frozen-thawed dacite in the dam site area of Tibet Rumei Hydropower Station as an example,the physical and mechanical properties of the frozen-thawed single-fractured dacite are studied by similar materials.At the same time,the damage constitutive model is established by using the theory of damage mechanics.The accuracy and rationality of the model have been applied and verified,and summarized as follows:(1)In terms of physical properties:(1)The dry mass,dry density,and wave velocity of the frozen-thaw single-fractured dacite decrease with the increase of the number of freeze-thaw cycles.The saturated water quality,saturated water density and water absorption rate of the frozen-thaw single-fractured dacite are just the opposite.(2)In addition to the number of freeze-thaw cycles,the above physical parameters are closely related to the dip angle of the crack,but no obvious correspondence has been found yet.(3)After comparative analysis,it is found that the rate of change of wave velocity and water absorption rate is relatively large after freezing and thawing,which indicates that the freezing and thawing effect has the greatest influence on the wave velocity and water absorption in the physical parameters of single jointed dacite.(2)In terms of mechanical properties: Generally speaking,freeze-thaw mainly deteriorates the mechanical properties,especially the compressive strength,elastic modulus and shear modulus.The fracture inclination determines the deformation process and failure mode,and also has an important influence on the mechanical parameters,especially on the compressive strength.Specifically,(1)with the increase of freeze-thaw times,the compressive strength,elastic modulus,cohesion,internal friction angle and shear modulus will gradually decrease,while the frost resistance coefficient and the roughness of fracture surface will increase.(2)With the increase of fracture inclination from 0° to 90°,the mechanical parameters such as compressive strength,elastic modulus,cohesive force,shear modulus and their changes will decrease first and then increase,reaching the minimum at 30°,and the change characteristics will not change because of the freeze-thaw or the number of freeze-thaw cycles.At the same time,Poisson's ratio and its changes will also change with the fracture.The dip angle varies,which shows that the fracture dip angle has an important influence on the mechanical parameters.(3)Deformation process of 0° and 90° inclined fracture specimens can be divided into compaction stage,elastic stage,fracture development stage and post-fracture stage.Deformation process of 30° and 60° inclined fracture specimens can be divided into compaction stage,elastic stage,macro-fracture compaction stage,elastic stage,fracture development stage and post-fracture stage.(4)In the absence of confining pressure,tension failure is dominant in the 0° and 90° fracture dip samples,while shear failure is dominant in the 30° and 60° fracture dip samples;in the presence of confining pressure,shear failure is dominant regardless of the dip angle.(3)In terms of damage constitutive equations,from the macroscopic and microscopic perspectives,the meso-damage constitutive relation of single-fractured dacite under freeze-thaw conditions is established,and then the macroscopic damage calculation method is derived based on the principle of energy conservation.Combined with the macroscopic and microscopic damage coupling relation,the macroscopic and microscopic damage constitutive model of the single-fractured dacite under the freezethawing and uniaxial compression load is obtained.On this basis,the damage constitutive relation of the single-fractured dacite under freeze-thawing and conventional triaxial load is derived.(4)In the application and verification of the model,the application of the model shows that the results of the model agree well with the experimental results,which shows that the model is reasonable.At the same time,it is found that the damage evolution process of intact dacite can be divided into linear damage and deceleration damage with the increase of strain under uniaxial compression,while the damage evolution process of frozen-thawed dacite with single fracture can be divided into damage weakening,accelerated damage,linear damage and deceleration damage.In conventional triaxial compression,with the increase of axial strain,the damage evolution process of intact and single-fissured dacite can be divided into damage weakening,accelerated damage,linear damage and deceleration damage.