Study On Mechanical Properties And Failure Mechanism Of Frozen-thawed Sandstone Under Impact Loading

There is a vast seasonal frozen area in the north of China.The rock mass in the seasonal frozen area not only bears engineering loads,but also undergoes freeze-thaw cycles for a long time.Blasting and mechanical rock breaking are commonly used construction methods in rock engineering,which impose high strain rate load on rock mass,making the environment of rock mass engineering more severe and complex,and bringing new challenges to the solution of rock engineering problems.In this paper,the rock mass engineering in the northern seasonal frozen area is taken as the research background,and the mechanical properties and failure rules of rock mass under the environment of saturated freeze-thaw and high strain rate are systematically studied by means of experimental research,theoretical analysis and other methods and means,with the help of saturated freeze-thaw test method and split hopkinson pressure bar test system.The specific results obtained are as follows:(1)The mechanical properties and failure rules of saturated freezing-thawing sandstone samples under static uniaxial compression were measured,and the variation rules of stress-strain curve,elastic modulus,peak strength,peak strain and poisson's ratio of rock samples with freezing-thawing temperature were obtained,and the sensitivity of mechanical properties of rock samples to freezing-thawing temperature was analyzed.The results show that the elastic modulus,peak stress and poisson's ratio of sandstone decrease with the decrease of freeze-thaw temperature,and the peak strain increases with the decrease of freeze-thaw temperature.With the decrease of freezethaw temperature,the failure characteristics of sandstone gradually change from tensile failure to compressive shear failure.(2)The mechanical properties and macroscopic failure rules of sandstone samples were measured under the coupling effect of freeze-thaw and high strain rate,using the split Hopkinson pressure bar test system,and the influence rules of freezethaw temperature and strain rate on rock dynamic mechanical properties were obtained.The study shows that with the decrease of freeze-thaw temperature,the dynamic elastic modulus and peak stress of sandstone decrease gradually,while the peak strain increases gradually,and the compressive strength and deformation resistance of sandstone was decreased.With the increase of strain rate,the dynamic elastic modulus,peak stress and peak strain of the specimen all increase gradually.(3)By means of fragmentation analysis method,fractal characteristic theory and energy dissipation theory,the influence law of freeze-thaw temperature and strain rate on the macroscopic failure characteristics of rock samples was analyzed,and the energy dissipation mechanism of rock samples under the coupling action of freeze-thaw and high strain rate was revealed.The results shown that with the decrease of freeze-thaw temperature,the degree of sample breakage increases and the energy consumption required for sample breakage decreases.With the increase of strain rate,the failure degree of the sample increases,and the dissipation energy ratio of the system to the sample breakage increases.The research results can provide reference for rock engineering design in freezethaw and high strain rate environments.