Experimental Study On The Influence Of Prefabricated Fissures On The Mechanical Properties Of Granite

Granite has produced natural joints,fissures and other defects in the natural growth and crustal movement.This defect is the main cause of rock mass instability.On the other hand,with the progress of our country's economic development,more and more large-scale deep underground engineering is builted,and the ground stress around the engineering affects the stability of the engineering.Therefore,researching on the mechanical properties of fissured granites under different lateral pressures has important practical engineering significance for the long-term stability evaluation of underground engineering,the identification and reinforcement of engineering damage.The paper takes granite as the research object.First,the granite sample is processed into a slab granite sample with three kinds of prefabricated fissures and pasted 4 axial strain gauges and 4 lateral strain gauges at the corresponding positions around the fissure on the front and back of the sample to measure the strain development of the granite sample near the fissure during the test.Through the axial ultrasonic wave velocity test system under the conditions of rock mechanics coupled triaxial experiment,the bidirectional compression test under different lateral pressures(2,5,10 and15MPa)of prefabricated single-fissure granite samples with different inclination angles was carried out.Through the analysis of peak strength,elastic modulus,Poisson's ratio,volumetric strain and crack initiation stress,the influence of fissures and lateral pressure on the mechanical properties of granite specimens is explored,and the anisotropy of fissured inclination and lateral pressure on granite is analyzed.The study found that the initial compaction stage of the sample gradually decreased with the increase of lateral pressure and fissured inclination angle,and the corresponding axial strain showed a gradually increasing trend when the granite sample failed.The peak strength of granite generally shows a trend of increasing with the increase of lateral pressure.When the lateral pressure increases to 15 MPa,the increase of peak strength weakens.The fissured inclination has a degrading effect on the mechanical properties of the granite test.The peak strength of the sample shows a gradual decrease with the increase of the fissured inclination.The elastic modulus of the sample shows anisotropic characteristics with the change of the lateral pressure.The Y direction(1,3position)shows a gradually increasing trend with the increase of the lateral pressure.When the lateral pressure increases to 15 MPa,the increase in elastic modulus weakens;there is no obvious change in the X direction(2,4 points).Poisson's ratio and volumetric strain have no obvious changes with the increase of lateral pressure.The crack initiation stress exhibits isotropic characteristics with the change of the lateral pressure,and its changing law is similar to the changing law of peak strength.The elastic modulus shows isotropic characteristics with the change of the fissured inclination.As the fissured inclination increases,the elastic modulus in the Y(1,3 position)direction and the X(2,4 position)direction show a gradual decreasing trend.There is no obvious change rule between Poisson's ratio and crack inclination angle.The volumetric strain exhibits anisotropic characteristics with the change of the fissured inclination.With the increase of the fissured inclination in the Y(1,3 position)direction,it shows a gradual decreasing trend;there is no obvious change in the X(2,4position)direction.The crack initiation stress exhibits isotropic characteristics,and the Y(1,3position)direction and X(2,4 position)direction show a gradually decreasing trend with the increase of the crack inclination angle.