Experimental Investigation On The Rupture Mechanism Of Rocks By Deviatoric Stress

Coal has long been the main energy source in China.With the depletion of shallow resources,deep mining will become the normal state of coal resource development.The complex mechanical environment of"three high and one disturbance-high ground stress,high earth temperature,high karst water pressure,and mining disturbance"in deep coal and rock mass leads to many difficulties and challenges in deep mining,among which the large deformation and failure mechanism of roadway surrounding rock has always been a problem that puzzles the safe and efficient mining of deep coal.The deviatoric stress controls the failure of rock and has important significance for the plastic failure of rock.Therefore,this paper uses the self-developed true triaxial loading experimental system(designed acoustic emission monitoring device)to study in detail the effects of deviatoric stress on deformation characteristics,strength characteristics,acoustic emission signal characteristics and failure modes of rock under different stress paths.And the deviatoric stress induced rock fissure expansion law.The self-developed true triaxial loading experiment system can realize precise control by electro-hydraulic servo control system,and can realize three-way independent loading.The maximum loading size is 200×200×200 mm~3.At the same time,the acoustic emission monitoring device is designed,which can realize that the test block is accurately monitored in real time.The full stress-strain curves of100×100×100 mm~3 mudstone and cement mortar were measured under uniaxial compression,and the values of different stages were selected as the intermediate principal stress values under different stress states.The test results under the state of biaxial loading indicate:With the increase of the intermediate principal stress,when the deviatoric stress of mudstone reaches the maximum value,the corresponding strain first increases and then decreases,indicating that the increase of the intermediate principal stress first strengthens the rock deformation ability;When the mudstone reaches 90%-100%of the maximum deviatoric stress,the number of acoustic emission events increases the most,while the cement mortar reaches 45%-75%of the maximum deviatoric stress,and the number of acoustic emission events increases the most,which indicates that the damage of different lithology lies different stages.The increase of the ringing count and the cumulative ringing count mainly occurs in the post-loading phase,and increases with the increase of the intermediate principal stress,indicating that the increase of the principal stress under different stress states will accelerate the damage of the test block;When the mudstone and cement mortar are destroyed,there is a boundary point between the deviatoric stresses.The failure modes of the two are layered ruptures.As the intermediate principal stress increases,the layered rupture phenomenon becomes more and more obvious.The failure modes are shear failure and tensile failure.The test results under true triaxial loading state indicate:With the increase of the intermediate principal stress,the corresponding strain decreases when the sample deviator reaches the maximum value,and the residual strength shows an increasing trend,indicating that the intermediate principal stress weakens the deformation resistance of the test block,and strengthen the residual strength of the test block;The ringing count is mainly concentrated in the loading stage after the test block,and the ringing count is positively correlated with the principal stress.With the increase of the intermediate principal stress,the cumulative ringing count of acoustic emission in the pre-loading stage and the post-loading stage shows a trend of increasing first and then decreasing,indicating that the intermediate principal stress has the effect of promoting the post-inhibition after the failure of the test block;When the mudstone and cement mortar are destroyed,there is a boundary point between the deviatoric stress.With the increase of the intermediate principal stress,the deformation mode of the mudstone changes from the“anti-V”shape to the positive“V”shape,and the cement mortar changes from the positive“V”shape to the opposite“V”shape and has obvious plastic deformation,and the damage mode is shear failure.The test results under the true triaxial loading and unloading state indicate:With the increase of the intermediate principal stress,the corresponding strain increases gradually when the deviatoric stress of mudstone and cement mortar reaches the maximum value,indicating that the increase of the intermediate principal stress strengthens the deformation capacity of the test block;The fastest increase in the number of sound emission events is different,indicating that the two largest damages occur at different stages.The ringing count is the highest at the peak strength of cement mortar,while the mudstone lags behind the peak strength.When the two are close to the peak intensity,the cumulative ringing count increases rapidly,indicating that a large number of elastic waves are generated when the test block is broken;When the mudstone and cement mortar are destroyed,there is a boundary point between the deviatoric stresses.The failure modes are lamellar ruptures.As the intermediate principal stress increases,the spallation phenomenon becomes more and more obvious.The failure mode is mainly tensile failure.Under different stress paths,the relative failure time of mudstone and cement mortar decreases with the increase of intermediate principal stress.Except for mudstone under biaxial loading,its strength increases with the increase of intermediate principal stress,and its peak strength increases first and then decreases with the increase of intermediate principal stress under other stress paths.The process of deviatoric stress-induced rock fissure development,expansion and penetration until failure is obtained.At the same time,the relationship between deviatoric stress and rock failure morphology under different stress paths is obtained.