Experimental Study On Crack Propagation Of Anchored Rock-Like Mass

There are a lot of defects in the natural rock mass,such as bedding,fissures and joints,which seriously affect the safety and stability of rock mass.At present,most domestic and foreign researchers use the method of adding anchors to rock mass to control the deformation and failure of rock mass.However,many engineering examples show that Rock mass engineering often has structural instability and rock mass failure under the anchoring action of anchor bolts.These are mainly caused by the crack propagation in the anchored rock mass.Under the action of external forces,the anchored rock mass will cause the redistribution of structural stress,resulting in cracks,thus reducing the cracks.The anchorage effect of anchor rod causes engineering accidents.Therefore,it is of great significance to study the variation of cracks in jointed rock mass with anchors for exploring the mechanical properties,failure mechanism and engineering design and construction of jointed rock mass with anchors.Therefore,This paper takes quartz sandstone in zhangjiajie area of hunan province as the research object,based on similarity theory,complete and different crack inclination anchored and non-anchored rock samples are manufactured.Uniaxial compression test and acoustic emission test were carried out on anchored and non-anchored rock samples by combining theoretical analysis with laboratory test.According to the test results,the failure characteristics and acoustic emission characteristics of the samples were studied.The main research results and related conclusions are as follows:(1)The mechanism of crack initiation and propagation of anchored and non-anchored rocks under load was studied by carrying uniaxial compression tests on anchored and non-anchored rocks with different crack inclinations.The results show that In the process of loading that the crack propagation form of anchored specimens is simple and the number of cracks is small,and the time of crack initiation is later.When the specimen is destroyed,the bolt connection does not break,and the failure characteristics of the bolt-free rock are opposite to those of the rock with bolts.(2)By collecting stress-strain signals of anchored and non-anchored rocks during loading,the strength characteristics of anchored and non-anchored rocks under loading are studied.The results show that compared to anchorless test pieces,the stress-strain curves of anchored specimens under loading are relatively smooth and there is no more stress sudden drop.The peak strength and residual strength of anchored specimens increase in varying degrees,and the peak strength of the anchorless specimens showed a rapid drop after the peak strength,and the peak strength of the anchored specimens showed a downward trend,and the residual strength increased significantly.(3)By observing the uniaxial compressive strength of anchored and unanchored rocks,it can be known that the compressive strength of the specimen with the anchored joint angle of the anchor is different from the compressive strength of the anchored joint without the joint by 0.050 MPa,and the specimen with no anchor joint inclination of 90°The compressive strength is different from the compressive strength of the anchorless and unjointed specimens by 0.254 MPa.It is considered that the joint dip angle 90°has little effect on the mechanical properties of the rock mass.In addition,the uniaxial compressive strength of different fracture dip angles of anchored and unanchored rocks first decreased and then increased,indicating that the influence of crack dip on rock mass strength is adapted to the anchored rock mass.(4)Acoustic emission testing system was used to collect signals during uniaxial compression test of anchored and unanchored rocks to study structural damage change characteristics of anchored and unanchored rocks.The results show that both the acoustic emission impact rate and the energy rate can well describe the damage change of rock structure,and the impact rate is more sensitive than the energy rate to reflect the energy of rock.Because of the existence of anchor rod,this can continue to resist part of the load.When the stress-strain curve reaches the peak strength,the acoustic emission energy rate and impact rate will increase sharply again during the loading process.