Experimental study on the creep acoustic emission of fractured sandstone reinforced by anchor rods

To investigate the reinforcement and crack-stopping effect of anchor rods on fractured rock masses, Triassic sandstone from the Xiaolangdi Reservoir area was selected and fabricated into double-fractured specimens. Subsequently, 1 and 2 horizontal anchor rods were used to reinforce the double-fractured sandstone specimens sequentially. Using the RLJW-2000 rock rheological servo tester and the PCI-II type acoustic emission (AE) tester, indoor uniaxial compression creep and AE tests were conducted under the same experimental conditions for the unanchored, singly-anchored, and doubly-anchored sandstone specimens. Based on the experimental results, the creep mechanical characteristics and the three-dimensional spatial evolution of the AE events of the specimens with different numbers of anchor rods were analysed. This study focuses on the reinforcement and crack-stopping effect of anchor rods on fractured rock masses. The experimental results indicate the following: (1) Compared with those of the unanchored specimens, the creep failure strengths of the singly- and doubly-anchored specimens increase by 7.79 % and 22.14 %, respectively. (2) At a stress level of 60 MPa, the axial strains of the single-anchor and double-anchor specimens decreased by 8.41 % and 32.97 %, respectively, compared to the corresponding strain of the unanchored specimen, and the radial strains decreased by 9.21 % and 28.13 %, respectively. (3) Anchor rods have a good reinforcement effect on fractured sandstone, enhancing specimen strength and reducing deformation. (4) With an increase in the number of anchor rods, the reinforcement effect of anchor rods on fractured rock masses strengthened, and the reinforcement effect of double anchors was superior to that of single anchors. (5) Compared with those of the unanchored specimens, under relatively low stress levels, when the AE events extended to the area where the anchor rods were located, the number of AE events for both types of specimens decreased significantly, forming a blank area in the AE events, and the blank area of the double-anchored specimens was larger than that of the single-anchored specimens. (6) With increasing stress, many AE events originated, expanded, and passed through the anchor rod area, indicating that the specimen was about to undergo creep instability failure. (7) The evolution characteristics of the AE events are in good agreement with those of the macroscopic cracks on the specimen surface. The AE characteristics indicate that anchor rods have a significant crack-stopping effect on fractured rock masses, suppressing the initiation, expansion, connection, and penetration of internal microcracks in the specimens. Moreover, the crack-stopping effect of double anchors is superior to that of single anchors.