Study On Mechanical Properties And Failure Modes Of Sandstone Under Triaxial Compression With Strike Inconsistency

In view of the fact that various structural planes often exist in rocks,which have a great influence on the mechanical properties and failure of rocks,this thesis produced sandstone with strike discordency,carried out uniaxial and triaxial conventional compression tests,and analyzed its mechanical parameters,such as peak strength,shear strength parameters,peak strain,elastic modulus,deformation modulus,etc.At the same time,the uniaxial and triaxial failure modes are analyzed and summarized,and the characteristic value of energy dissipation coefficient is found through energy analysis.The main results and conclusions are as follows:(1)Through uniaxial and triaxial compression tests on sandstones with different structural plane parameters,the corresponding stress-strain curves are obtained,and the law is summarized and analyzed.It is found that the stress-strain curves of sandstones with different structural plane parameters can be roughly divided into microfracture compaction stage,elastic stage,yield stage and failure stage.For the triaxial compression test,the peak slope of the stress-strain curve moves upward to the right with the increase of confining pressure,and the range of peak strain decreases,indicating that the influence of confining pressure on the mechanical properties of the structure decreases.(2)Based on the analysis of mechanical parameters of uniaxial and triaxial sandstones,it can be concluded that the order of influence of structural plane parameters on mechanical properties is structural plane dip Angle > structural plane difference Angle > rock bridge length.With the increase of confining pressure,mechanical parameters such as peak stress,peak strain and elastic modulus increase to varying degrees,and the fitting of peak strength reflects a good linear relationship.At the same time,confining pressure will also weaken the influence of different structural plane parameters,and the weakening effect is opposite to the degree of influence,that is,the greater the influence of structural plane parameters on mechanical properties,The effect of confining pressure is reduced to a greater degree.(3)With the increase of the difference Angle of the structural plane,the peak strength fluctuates up and down in a small amplitude,and the overall trend is increasing.The peak strain,elastic modulus and deformation modulus increase with the increase of the difference Angle of the structural plane.With the increase of the length of the rock bridge,the peak strength first increases and then decreases,and the overall trend is upward.The peak strain and elastic modulus first increase and then decrease with the increase of the length of the rock bridge.The peak strain reaches its maximum value at20 mm,and the elastic modulus generally reaches its maximum value at 30 mm.The peak strength,cohesion,elastic modulus and deformation modulus all increase with the increase of structural plane dip Angle.(4)Through uniaxial and triaxial failure modes analysis,the failure modes of sandstone with different structural plane parameters are divided into five types: integral shear failure,shear failure through single structural plane,general tensed-shear mixed failure,tensed-shear mixed failure through plane shaped like "c",and "x" shear failure.The difference Angle of structural plane is the main factor affecting the failure mode,and with the increase of confining pressure,the shear characteristics in the failure mode gradually become obvious.When the difference Angle of structural plane is greater than80°,tensile cracks appear.When the length of rock bridge is greater than 20 mm and the Angle of structural plane is greater than 45°,the specimen is more broken after compression.(5)The dissipated energy and elastic energy are analyzed by uniaxial energy diagram,and the ratio of dissipated energy and elastic energy is defined as the dissipated energy coefficient.It is found that the energy change can better match and explain the four stages of rock failure,reflecting the elastic-plasticity of rock.The dissipated energy coefficient first increases slightly and then decreases,and then increases sharply during failure.The larger the peak value of the dissipated energy coefficient in the crack compaction stage is,the more likely secondary cracks will be formed and more failure surfaces will be generated during failure.The critical value of the dissipated energy coefficient is 2.