Experimental Study On Creep Acoustic Emission Characteristics Of Fractured Sandstone With Anchor Under Uniaxial Conpression

A large number of engineering practices show that in anchorage engineering,the rupture instability of rock masses does not occur at the beginning but evolves gradually under the action of continuous,constant engineering loads,i.e.,the deformation gradually accumulates with the growth of time,and creep damage instability eventually occurs.Therefore,it is important to study the influence of anchors on the creep mechanical properties and crack extension evolution characteristics of fractured rock masses,which are important for the stability of rock engineering.In this paper,by making double fissures in Triassic sandstone in the Xiaolangdi reservoir area of the Yellow River and reinforcing them horizontally with one and two anchors in turn,uniaxial compression creep acoustic emission tests under the same test conditions were conducted to study the creep mechanical properties and acoustic emission characteristics of fissured sandstone with different anchor numbers,and the effects of anchor numbers on the number,energy,extension direction,and extension range of microcracks in fissured sandstone were compared and analyzed.Finally,the effect of anchor rods on the reinforcement of fractured sandstone to stop cracking was proposed.The main findings of the study are as follows:(1)The number of anchors had a large effect on the creep damage strength and long-term strength of the fractured sandstone specimens.The creep damage strength and long-term strength of single anchor specimens increased by 7.79% and 35.93%,respectively,compared with those of unanchored specimens;the creep damage strength and long-term strength of double anchor specimens increased by 22.14% and 49.88%,respectively,compared with those of unanchored specimens.The number of anchor rods was increased from 0 to 1 and 2in order,and the degree of improvement of the mechanical properties of the specimens by the anchor rods increased gradually with the increase in the number of anchor rods.(2)At a stress level less than the long-term strength,the acoustic emission activity of each specimen was weak,with low values of amplitude,ringing count,energy,and a low number of peak frequency bands.When the stress level is greater than the long-term strength,the acoustic emission activity of each specimen increases with the increase in stress level,the amplitude,ringing count,and energy values increase,and the number of peak frequency bands increases.The amplitude,ringing count,energy,and peak frequency of acoustic emission generated by the specimens decreased with the increase of the number of anchor rods from 0 to 1 and 2 in sequence,and the anchor rods played a reinforcing role on the sandstone specimens and reduced the release of energy during the damage of the specimens.(3)The acoustic emission event point can better reflect the sprouting and expansion of microcracks inside the specimen.Under the same stress level,the number of acoustic emission event points produced by unanchored and anchored fracture specimens was different,and the number of acoustic emission event points produced by anchored fracture specimens was lower than that of unanchored specimens,and the number of acoustic emission event points produced by double-anchored specimens was significantly lower than that of single-anchored specimens,indicating that the reinforcement and anti-cracking effect of two anchors on the specimens was better than that of one anchor.(4)The number of anchors had a significant effect on the fracture penetration pattern of the fractured sandstone specimens.Only one flat fissure penetrated the bridge part of the single-anchored specimen,while multiple annular fissures penetrated the bridge part of the double-anchored specimen.The single anchor could strengthen the bridge part of the specimen but failed to change the direction of fracture expansion,while the double anchor could not only strengthen the bridge of the specimen but also change the direction of fracture expansion and thus change the damage mode of the bridge.The tensile and shear properties of the anchor can play a role in inhibiting the crack expansion and strengthening the macro-mechanical properties of the rock,i.e.,the reinforcement and anti-cracking effect of the anchor.