Dynamic Uniaxial Compression Test And Energy Dissipation Analysis Of Jointed Rock

The natural rock mass is very complex,and the rock mass contains a large number of micro-cracks and joints.Such micro-cracks,joints and other structures have a great impact on the physical and mechanical properties of the rock mass.The strength of the rock mass will be affected by the existence of these structural surfaces.affected.The structural planes existing in the natural rock mass will not only affect its mechanical properties,but also cause a large change in the longitudinal wave velocity of the rock.Under static and dynamic loads,the research on the strength characteristics,failure modes and energy characteristics of jointed rocks has always been a hot spot in the field of geotechnical engineering.In order to explore the physical and mechanical properties of jointed rock masses,the joint filling material and filling thickness are used as basic variables to measure longitudinal wave velocity,static uniaxial compression test and dynamic uniaxial compression test and conduct theoretical analysis.Three materials of cement slurry,cement mortar and gypsum were used as filling materials,and three thicknesses of 5mm,10mm and 15mm were used as filling thicknesses.Two types of joint specimens were made respectively,and epoxy resin was used to bond the joint parts with the rock.Together,the longitudinal wave velocity measurement and the static and dynamic uniaxial compression test are carried out to analyze the energy change law of the joint specimen under the impact air pressure of 0.3 MPa,0.5 MPa and 0.7 MPa.The main research contents and conclusions are as follows:(1)An ultrasonic detector was used to measure the longitudinal wave velocity characteristic parameters of the two types of joint specimens.It is concluded that different filling materials and filling thicknesses have significant effects on the changes of longitudinal wave velocity of jointed sandstone specimens.The wave speed reduction of the sandstone specimens filled with cement mortar joints is the smallest,and the wave speed reduction of the sandstone specimens filled with gypsum joints is the largest.The wave velocity of jointed sandstone is negatively related to the thickness of the joint.As the thickness of the sandstone joint increases,the wave velocity of the sandstone gradually decreases.(2)The static uniaxial compression test shows that the compressive strength of the test piece gradually decreases with the decrease of the strength of the filling joint material and the increase of the filling thickness.The stress-strain curve of the joint specimen is divided into the initial compaction stage,linear elastic stage,plastic deformation failure stage and post-peak fracture stage.The failure of sandstone specimens with different joint materials is mainly tensile failure,and the failure of sandstone specimens with different joint thicknesses is mainly tensile-shear failure.(3)Through the SHPB impact compression test,it is concluded that as the strength of the filling material increases,the dynamic elastic modulus of the joint specimen gradually increases,and the dynamic compressive strength decreases linearly;with the increase of the filling thickness,the initial dynamic elasticity of the joint specimen The modulus is smaller than that of the complete specimen,and the dynamic compressive strength decreases exponentially.The impact failure form of the complete specimen is mainly tensile split failure,and the specimen containing joints is mainly a composite failure form of compression-shear failure and tensile failure.(4)The law of energy dissipation of joint specimens is analyzed.In the case of the same incident energy,the reflected energy ratio gradually increases as the strength of the filling material decreases,and the transmission energy ratio and energy dissipation ratio gradually decrease;as the joint thickness increases,the reflected energy ratio and the dissipation energy ratio increase The transmission energy ratio gradually decreases.The uniaxial impact compression test was performed on specimens filled with cement mortar under different impact air pressures.The incident energy increased with the increase of impact air pressure,and the energy absorption and crushing energy density of the specimens increased with the increase of incident energy,in linear proportion Relationship:The crushing energy density has a linear relationship with the average strain rate of the specimen,and the dynamic compressive strength of the specimen also has a linear relationship with the crushing energy density,and the fit is good.Figure 37 table 16 references 77...