Experimental Study On Creep Rupture Characteristics Of Double Fractures Fine Sandstone And Anchoring Effect Of Bolt Reinforcement

In this paper,uniaxial compression creep acoustic emission experiments were carried out for fine sandstone with two pre-existing fissures and fissured rock specimens bolted with different number of anchors by the RLJW-2000 servo-controlled triaxial rheological test system of rock and PCI-II AE system.The crack propagation process and the anchoring effect of the anchor on the fissure specimen are studied.The experimental results show as follows:(1)The failure mode of specimens with two pre-existing fissures takes mainly on mixed mode(tensile and shear).The crack starts from the inner tip of the two pre-existing fissures,and with the increase of stress,the microfracture extends,connects and penetrates along the direction of the pre-existing fissure to the upper and lower ends of the specimen,leading to the failure of the specimen.The effect of pre-existing fissure length on fracture failure mode: the longer the pre-existing fissure is,the simpler the main fracture form of the specimen becomes,and the failure surface is more straight;The shorter the pre-existing fissure is,the more complex the main fissures in the final failure of the specimen becomes,the more complete the damage is,and the cracks are mostly curved.This is consistent with the spatial evolution of acoustic emission events.(2)With the complete specimen as the standard,the pre-existing fissure length is 20 mm and 30 mm,the creep damage intensity decreased by 37.66%,65.71%.The pre-existing fissure length has a significant impact on the strength of the specimen.(3)The creep damage strength of the horizontal single anchor specimen and the horizontal double anchors specimen increased by 7.79% and 22.14%,respectively,with the specimen without bolt as the standard.The effect of anchoring on the crack specimen is obvious,and the effect of double anchor reinforcement is greater than that of a single anchor.(4)Compared with the specimen without bolt,the acoustic emission locating point of the anchor specimen is obviously reduced when it is extended to the position of the bolt.When the macroscopic fissure of the anchor specimen is extended from the surface to the bolt position,the wedge-shaped failure surface is formed,and the forms of cracks and failure surface are mostly curved surface,the anchors act as a deterrent to the expansion of the fissures and at the same time alter the original spreading direction of the fissures,the inhibition of the double anchor is greater than that of the single anchor.