Rockburst in roadway happened along with a large-scale destruction of the surrounding rock. To study the failure laws of the surrounding rock in the process of rockburst in roadway, the evolution behaviors of the plastic zone and the criteria of large-scope failure were studied by using FLAC numerical simulation. Meanwhile, the stress response laws of the plastic zone were studied by loading or unloading in a single direction. The results showed that, in the 20 MPa stress environment, large-scale failure zone would appear when the maximum confining pressure was loaded to 50 MPa or the minimum confining pressure was unloaded to 6 MPa. Loading in the direction of maximum confining pressure or unloading in the direction of minimum confining pressure, when the stresses reached a certain limit, could lead to a large-scale expansion to the failure zone of the surrounding rock a roadway. Meanwhile, the stress response of the plastic zone became more sensitive, which might easily trigger rockburst in roadway. In addition, two sine qua nonstress conditions for rockburst in roadway were determined: high stress ratio and high stress level. This might provide a theoretical basis for the stress source mechanism of roadway rockburst.
The source of energy release when rockburst occurs must be determined to understand the mechanisms underlying disaster formation and achieve accurate prevention and control. Although previous research has systematically investigated the energy source underlying rockburst from different perspectives, issues such as an unclear understanding of the energy accumulation state and inaccurate positioning of the energy release source remain to be resolved. In this study, the “1·17” major roof accident in the Danshuigou Mine was used as the background to evaluate and analyze the stress environment and energy accumulation characteristics of roadway surrounding rock under multiple mining disturbances, and the results showed that a super energy package occurs in the surrounding rock of the mining roadway. Subsequently, the evolution process of energy in this region and the mechanism of induced rockburst were elaborated. The results showed that the degree of stress concentration in the surrounding rock of the roadway will increase several times as the number of mining disturbances increases. Under the influence of multiple mining disturbances, the maximum principal stress peak of the surrounding rock of the roadway can reach 5–10 times the maximum principal stress value outside the mining-affected area. A large amount of elastic energy was accumulated in the rock surrounding the roadway, and super-high-density energy packages were formed locally. The maximum energy density value reached 50–185 times the value observed in areas outside the mining-affected zone. Thus, rockburst may be induced when the large amount of energy accumulated in the super energy package is suddenly and violently released; moreover, the degree of energy accumulation in the super energy package is likely closely related to the magnitude of rockburst. These results have important theoretical significance and application value for clarifying the mechanism of rockburst and improving the effectiveness of rockburst prediction and prevention.
Fault dislocation occurs under certain stress conditions. Based on the mechanical relationship between the direction of crustal stress and fault occurrence, three criteriafault dislocation trend, fault strike dislocation trend, and dip dislocation trend-are put forward. According to these three criteria, the fault slip and the type of slip can be inferred. The parameters that have great influence on the characteristics of fault slip are fault dip angle, angle between horizontal principal stress and fault strike, depth, lateral pressure coefficient, internal friction angle, and cohesion of fault plane. Fault slip is more likely to occur in the environment of high deviation stress, low friction angle, and dip angle of about 40 •. Fault rupture is a point-to-surface and deep-to-shallow process. When the criterion value of the local position of the fault is greater than 0, it will lead to the slip of the nearby fault. When the slip range of the fault extends to the surface, it will cause large earthquakes with large-scale surface rupture. The theoretical calculation is basically consistent with the numerical simulation results. According to the theory in this paper, the slip instability state of Longmen Mountain Fault Zone under different stress conditions is calculated, and the results show that when the lateral pressure coefficient is greater than 2.5, dislocation occurs in the deep part of the fault.
According to the theories of rockburst based on butterfly-shaped plastic zones, a plane strain mechanical model was established for stress distribution around the holes in homogeneous elastoplastic media. Based on the Mohr-Coulomb yield criterion and the generalized form of Hooke’s law, the equation for the elastic strain-energy density of units at a 3D stress state was deduced. On this basis, the energy absorption and release in rocks surrounding a roadway during the evolution thereof in a coal reservoir tend to rock bursting were quantified. Through Flac3D 5.0 numerical simulation software, the energy released from a homogeneous circular roadway at different development states of plastic zones was investigated. By investigating conditions at the 21141 working face in Qianqiu Coal Mine, Henan Province, China, subjected to rockburst, a numerical model was established to calculate the energy released by a rockburst working face. The calculated results approximated the data monitored at the outburst site, with the same energy level recorded. The theoretical calculation for energy release from the rock surrounding a roadway is expected to reference engineering practice.
Large-scale expansion of failure areas in rocks surrounding underground cavities causes severe destruction of the underground space and may trigger serious disasters. To study the large-scale failure mechanism and expansion laws of rocks surrounding underground cavities, we performed a theoretical study of the distribution characteristics of the stress field around a circular cavity and determined the directional sharp-point failure mechanism by analysing the stress destructive power using the three elements of the Mohr circle. Results showed that, along the circumferential direction, the stress destructive power increases first and then decreases, showing a sharp-angular distribution. Rock with any properties will suffer priority damage at the stress sharp point. The direction criterion of the stress sharp points was proposed, and the direction of these points showed a convergent behaviour in the radial direction of the cavity, tending to be stable at 40°-50° beyond five times the cavity radius. In addition, the results were verified by FLAC3D numerical simulation. The theoretical analysis for the ideal circular cavity may provide references to study the damage laws of rocks surrounding other irregular-shaped space, as well as providing a theoretical basis for the prevention and control of underground engineering disasters.
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