Macro-micro Mechanical Research On Shear Failure Acoustic Emission Properties Of Bolted Rock Joints And Failure Mechanism

Fractured rock mass exists in complex geological environment, it is a kind of complex geological body which is often encountered in geotechnical engineering and environmental engineering and it was composed of rock blocks and fracture planes. In order to limit deformation of fractured rock mass and improve the stability of fracture rock, anchor reinforcement is often used in engineering. As one of the main means of rock mass support, the reinforcement effect of rock bolt is very obvious. But the reinforcement mechanism of rock bolt,especially under the condition of long-term complexity, the reinforcement mechanism of the anchor to the rock mass joint has not been fully understood. In the construction of hydraulic and hydropower engineering, underground state oil reserves and deep resource exploitation, it was important to consider the stability of the construction period and make sure that the days after long-term operation safety. Therefore, the anchoring effect of rock mass joint under complex geological factors and engineering conditions has been paid more and more attention in various engineering practice and scientific research.In this paper, based on the research of Huangdao State Oil Reserves project,an integrated approach was taken which includes theoretical analysis, indoor test,and numerical simulation. In this study, the mechanical property and macro-meso mechanism of bolted jointed rock under shear load are in-depth studied. The key findings are given as follows.(1) The shear strength and deformation characteristics of anchor joint surface are studied. The shear deformation of the bolt occurred obvious shear deformation in the section about 3-4 times of the diameter of the bolt It is shown that the deformation of the shear direction and axial deformation. The effective length of the obvious shear deformation of bolt, the average shear stress distribution on each surface of the bolt is related to the contact condition between the bolt and the hole wall. Under the condition of compressive shear stress, the compression sliding phenomenon occurs on the original crack plane and the branch crack will be formed at the tip of the original crack plane.(2) Based on the results of direct shear test of bolted rock joint, the law of roughness coefficient and anchoring condition to the peak strength of anchor joint is analyzed. And with the use of acoustic emission monitoring system,studied the shear failure mechanism of anchorage. The results show that: as for the bolted joint, the shear strength increases with the increase of roughness,while with the increase of the elongation rate of anchor, the peak shear strength of the anchor structure is decreasing. The lower the extension rate, the more obvious the strain softening after the peak shear strength. With the decrease of the elongation of anchor bolt, the anchoring effect is more obvious, however, in the post peak stage, the stability of anchored rock mass decreases with the decrease of the elongation of the bolt, and there will be a large mutation stage.The extension rate is too low will lead to the sudden fracture of the bolt, which leads to the instability of the anchor joint .When the rock from the anchor state to non-anchorage state, the damage of anchor rock is decreasing gradually. The crack distribution of the non-anchor plane is relatively uniform, and most of them focus on the protuberance of joint surface. While the crack of the anchor joint is mainly distributed in the surrounding area of the bolt, there are many cracks around the anchor. Along with the increase of the bolt elongation, the area of the crack around the anchor bolt is gradually decreasing.(3) By using the Particle Flow Code (PFC2D), failure mechanism on anchoring of rock joint under different inclination anchor and macro-micro study on failure mechanism of rock mass anchorage joints under different roughness are simulated. In the shearing process of bolted rock joint, the contact force evolution, micro-crack initiation and development, energy dissipation, the distribution of particle orientation angle of bolted joint and particle rotation evolution are in depth analyzed. Further, the macro-meso characteristics and anchoring mechanism in shear process of bolted rock joint are deeply revealed.