Study On Mechanical Properties Of Thick-walled Cylinder Granite

After the mining of mineral resources enters the deep part,its occurrence condition and mining environment become complex,the mining difficulty is increasing.Additionally,the mining cost is also increasing.The excavation of roadway would change the original stress balance state,which leads to the loading and unloading of the surrounding rock near the free surface.Compared with the initial stress,the tangential stress of rock mass increases,while radial stress decreases.Moreover,the rock mass is often in the non-uniform stress state.Therefore,the study on the mechanical properties of rock under the non-uniform stress state has considerable theoretical significance and application value.In this paper,thick-wall cylinder granite was taken as the research object,uniaxial compression and conventional triaxial compression tests were conducted on granite samples with different pore sizes by using the MTS815 electro-hydraulic servo rock mechanics test system,and the strength,deformation and failure characteristics of granite samples with different pore sizes and confining pressures were analyzed.The main research results are as follows:(1)Under uniaxial compression,the peak strength,deformation characteristics and elastic modulus of the intact sample and the thick-walled cylinder sample had little difference.Moreover,the pore diameter had little influence on the mechanical properties of the rock under uniaxial compression.Under triaxial compression,the stress-strain curves of the complete specimen and the thick-walled cylinder specimen had no obvious yield platform.The peak strength of intact and thick-walled cylinder specimens increased with confining pressure.When confining pressure was small,the strength difference between specimens with aperture of 10 mm,15 mm,20 mm and complete specimens was small;when confining pressure reached 30 MPa,the strength of specimens with aperture of 15 mm and 20 mm was obviously low.Under the same confining pressure,the elastic modulus of thick-walled cylinder specimens had little relationship with the aperture.(2)The failure mode of thick-walled cylinder specimens under uniaxial compression was tension-shear failure,There is no obvious sign of pre-rupture in the wall of the hole.while the main failure mode under triaxial compression was shear failure.In triaxial compression of thick-walled cylinder specimens.Lamellar failure occured along the circumference of a thick-walled cylinder specimen during triaxial compression,whose shear area decreased with the increase of confining pressure,and the thick-walled cylinder samples with 10 mm and 15 mm pore diameter under high confining pressure were stripped,while the samples with 20 mm pore diameter under different confining pressures were strippedobviously.(3)With the increase of confining pressure,the influence parameter m value of three-dimensional H-B criterion increased,indicating that the strength of sample increased with the increase of confining pressure.Under the same confining pressure,the m value of each point from the outer wall of the cylinder to the inner wall showed an increasing trend,the bearing capacity of the sample became lower and lower.Additionally,the hole wall was most likely to be damaged,which was consistent with the results of theoretical analysis.