Abstract
Grouting reinforcement is one of the most effective methods to enhance the stability of the goaf, and its scheme selection, hole location, and parameter determination directly affect the success or failure of goaf treatment. On the basis of discussion of the deformation mechanism and evolution law of the longwall goaf, this article comprehensively analyzed the grouting reinforcement mechanism of the goaf combined with filling theory, permeability theory, and fracturing theory and studied the physical and chemical reaction principles of two commonly used filling materials, cement-fly ash slurry and cement-clay slurry. Three grouting models have been established: whole grouting, local grouting in fracture zone, and strip grouting, and then simulated the grouting effect of the two more common methods of whole grouting and strip grouting by numerical simulation software (FLAC3D, tecplot, Surfer). Simulation analysis is carried out from the perspectives of settlement deformation, horizontal movement, vertical stress, and horizontal stress. Finally, the feasibility of grouting treatment in the goaf is verified by engineering example. The results show that a reasonable grouting scheme can effectively reduce the residual deformation of the goaf and its overlying rock and improve the poor stress state, so as to achieve the purpose of effective grouting.
Highlights
Construction land has gradually become a scarce resource in mining cities and their surrounding areas with the continuous acceleration of urbanization; sometimes, the land above the goaf has to be used to meet construction needs
The risk of secondary activation exists in the goaf because of its complex structure and susceptibility to groundwater, earthquake, external loads, and other factors; its stability degree directly restricts the size, volume, and safety of the proposed building [1,2,3]
After the initial model without grouting reaches a stable state (Figure 5), the maximum residual subsidence value of the ground surface is 43 mm, the residual subsidence coefficient is about 0.011, and the maximum subsidence value is located directly above the goaf, which is mainly due to further compaction of the rock mass in the goaf and caving zone and the closure of the separated layer and gap in the fracture zone; horizontal movement is mainly concentrated on both sides of goaf and the surface above the goaf
Summary
Construction land has gradually become a scarce resource in mining cities and their surrounding areas with the continuous acceleration of urbanization; sometimes, the land above the goaf has to be used to meet construction needs. The grouting technology has a wide range of applications in these countries It has expanded from simple foundation reinforcement and water plugging penetration in mines to hydraulic engineering, bridge and airport construction, and other fields. Based on the analysis of the mechanism of residual settlement in the old goaf and the theory of mining subsidence, Deng et al [4] studied the technical method of grouting and filling to control residual settlement in the old goaf. Lu et al [9] established the relationship between the residual movement angle, the mining depth, and the equivalent mining thickness of the old goaf and proposed the determination method of the filling and grouting range in the old goaf. The grouting technology in the goaf is a concealed project, but there is no mature theoretical basis and technical support in the scientific community. Based on the mechanism analysis, this study analyzed the grouting effect of different grouting models by means of numerical simulation
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