Abstract
To address the prominent status of great deformation and difficult maintenance of the roadway under high stresses, this study investigated the mechanical characteristics of surrounding rocks and bearing structural stability in a roadway under adjustment and redistribution of stresses through theoretical analysis, numerical simulation, and engineering field test. Stability forms of the bearing structure of roadway surrounding rocks were analyzed by using the axis-changing theory from the perspectives of surrounding rock, mechanical properties of roadways, surrounding rock stress distribution, and mechanical mechanism of the bearing structure. It is suggested that the surrounding rock stress distribution state is improved and the bearing structure is optimized through unloading and reinforcement construction. A mechanical model of roadway excavation was constructed to analyze the influences of excavation spatial effect on the stress releasing and bearing structure of surrounding rocks. A rock postpeak strain softening and dilatation model was introduced to investigate the mechanical characteristics of the surrounding rock mass in the rupture residual zone and plastic softening zone in a roadway. Moreover, we analyzed the influences of unloading and reinforcement construction on the stress path and mechanical characteristics of the rock unit model, which disclosed the adjustment mechanism of the bearing structure of surrounding rocks by the failure development status of rocks. A numerical simulation on the distribution of surrounding rock stress fields and adjustment features of the bearing structure after roadway excavation and unloading and reinforcement construction was carried out by using the FLAC3D program. Results demonstrate that the unloading construction optimizes the axial ratio of spatial excavation in a roadway and the reinforcement zones on both sides are the supporting zones of the bearing structure. Moreover, the ratio between the distance from two side peaks to the roadway sides and the distance from the roof and floor peaks to the excavation space is equal to the coefficient of horizontal pressure. In other words, the final collapse failure mode of surrounding rock is that the long axis of the excavation unloading space points to the same direction with the maximum principal stress of the primary rock. Reinforcement forces the surrounding rocks to form a “Ω-shaped” bearing structure, which is in favor of the long-term maintenance of the roadway.
Highlights
The mining intensity of coal mines is increased, and the mining depth increases continuously due to the increasing exhaustion of shallow resources
Surrounding rock stresses are adjusted again for secondary bearing of surrounding rocks in the initiative bearing zone, cracks in compressed surrounding rocks expand to deep regions along the radial direction, and secondary cracks are produced. e passive bearing structure of deep is motivated to undertake the high stress and protect the shallow broken surrounding rocks (Figure 12(b))
Numerical Simulation Schemes and Modeling. e largediameter pressure-relief drilling is used in the field construction of high-stress roadway. erefore, largediameter pore based unloading of roadway surrounding rocks and surrounding rock stress field distribution characteristics after reinforcement as well as their influences on surrounding rock stability were simulated by FLAC3D software; it is used to verify the above theory
Summary
The mining intensity of coal mines is increased, and the mining depth increases continuously due to the increasing exhaustion of shallow resources. E joint supporting technology based on the new Austrian tunneling method believes that a complicated highstress roadway only considers that increasing the supporting intensity of surrounding rock is difficult to achieve the expected effect and the supporting principle shall observe the principle of “flexible first and rigid, resistance-yieldresistance, appropriate flexibility and yield, yield-resistance combination and stable support.” e axis-changing theory proposed by Yu and Qiao [16, 17] believes that surrounding rock failure in a roadway is caused by excessive stresses over the strength limit of rock mass and the axial ratio for roadway excavation is changed due to the collapse and deformation of surrounding rock, triggering stress redistribution of surrounding rock until realizing stable collapse of broken surrounding rocks [18]. Based on the spatial effect theory, uniform strength criteria, and nonassociated flow rule, a postpeak strain softening and dilatation model was introduced, which theoretically disclosed the control mechanism of unloading and reinforcement construction over the stress distribution state and deformation characteristics of surrounding rocks on the free face. Such adjustment mechanism was verified through a numerical calculation and field application effect. is study has important references to surrounding rock control in a highstress roadway which is difficult to be supported
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