Research On Control Technology And Application Of Grouting Reinforcement Of Deeper Fragmenting Coal And Rock Mass

Coal occupies a critical position in the energy structure of China,and the coal industry is a pillar of Chinese economic development.By the end of 2020,China will have consumed approximately 4.2 billion tons of coal,which is approximately 62%of the total energy consumed.For a fairly long period in the future,coal will remain the main energy source,and its status as a nonrenewable energy source will not change.Due to large-scale mining of coal resources,shallow coal has been depleted;coal mines must resort to deep mining,and the mining depth is increasing at a rate of 8-12 meters per year.Deep mining faces are affected by high ground stress,and coal-rock bodies tend to fail in roadways,which severely affects coal production.By targeting the damage characteristics of deep f'ractured coal-rock bodies and the shortcomings of grouting processes and materials,bringing in engineering project practice,and using traditional superfine sulphoaluminate cement clinker and a lime-gypsum mixture as raw materials,it is of great significance for the development of high yield and high efficiency and safe production of coal mine in China.this paper develops a new double-fluid inorganic grouting material that is suitable for reinforcing the grouting in deep fractured coal-rock bodies.The new grouting material significantly decreases cost and increases grouting project economy.Through indoor tests of material properties and simulations of grouting in fractured coal-rock bodies,the operability of the new grouting material is analyzed.The analysis reveals the grouting reinforcement mechanism for fractured coal-rock bodies from a microscopic perspective and promotes the industrial production of the new grouting material.Moreover,the new grouting process is based on the characteristics of damage to coal-rock bodies,and methods and indexes for evaluating the grouting and its ability to reinflorce fractured coal-rock bodies are studied.Engineering applications are tested,and a series of research results are obtained.By comprehensively reviewing the characteristics of the crack distribution and the stress concentration,the rock surrounding the roadway is divided into four regions according to the degree of damage:a complete fracture region,a reduced fracture region,a fractured compression region,and a quasi-original rock region.The complete fracture region has high permeability;the grouting in this region is extensive and mainly filling,and the anchor holes in this region strongly influence the grouting in the open coal body,weakening the effectiveness of increasing the grouting pressure at increasing the grouting consolidation depth and,thereby,inevitably inducing serious grouting leakage.High-viscosity grouting materials that consolidate quickly should be used at low pressure and low flow rate for grouting in this region.The penetration channels in the reduced fracture region are mostly large cracks.Because the cracks in this region are less developed than those in the complete fracture region,penetration grouting is the focus in this region.The grouting material used in this region typically has high permeability and low viscosity and is applied with medium or high pressure.The fractured compression region is affectedby concentrated stress;the cracks are compressed with small micro-cracks and poor connectivity.Split grouting under high pressure using low-viscosity and high-permeability materials should be the main approach.The quasi-original rock region is not too different from the original rock;it mainly contains primary cracks.Therefore,split grouting under high pressure using materials with low viscosity and high permeability should be the dominant approach.Using cement-based composite material grouting techniques and the orthogonal test method,the optimal recipe for a new grouting material is determined.One hundred portions of single-liquid sulphoaluminate cement clinker are prepared;they contain 1%plasticizer,0.9%thickener,and 0.6%retarder,and 87.5 portions of single-liquid gypsum and 12.5 portions of lime are prepared;they included 1.5%plasticizer,0.6%thickener,0.9%retarder.2%accelerator 1,0.22%accelerator 2,and 6.0%accelerator 3.Using a self-designed testing system,the optimal consolidation time for the grouting based on the new reinforcement material was determined to be 2 min,and the mortar diffusion radius was found to be 2 m through micro-analysis.It was concluded that the higher the content of hydrates in the new grouting material in the mortar and the transition region at the coal-rock interface is,the higher the degree of crystallization is and the better the strengthening effect of the grouting reinforcement is.The cementation type of the mortar based on the new grouting reinforcement material at the coal-rock interface is described by the Zimbelinan model.With respect to the mechanism controlling the grouting's reinforcement of a fractured coal-rock body and the reinforcement characteristics,methods for testing and indexes for measuring the grouting's reinforcement of a fractured coal-rock body were proposed.These included the mortar filling rate method(the grouting rate should be>90%),the mechanical parameter method(after grouting,the compressive strength should be more than 80%of the unaffected stratumundefineds compressive strength,the flexural strength should be more than 75%of the unaffected stratumundefineds flexural strength,and the porosity should be less than 10%.,and porosity of less than 10%),the split water injection method(with borehole leakage of less than 20 L/5 min),and the coring method(at a coring rate of>90%).Additionally,equations for calculating the reliability of the grouting reinforcement system were derived for each subsystem,the overall grouting system,and the different units in the system.A new inorganic grouting material has been produced on an industrial scale.Additionally,a field application test of the new inorganic grouting material has been conducted,and its superiority and adaptability have been verified.The study results were applied to reinforcing the fractured coal-rock body in a mine of the Jincheng Anthracite Mining Group,Jincheng,Shanxi.Outstanding results were obtained,and the economic and social benefits were significant,which shows that the new grouting material has very broad engineering application prospects.Moreover,the study of this material and its technical application to resource integration in residual mining areas,such as backfilling and recovering empty goaf-side roadways,and the study of resource integration in residual mining areas with respect to rock deformation and failure characteristics and safe recovery techniques received second place in the competition for the Science and Technology Award presented by the China National Coal Association in 2016 and 2017,respectively,which provides further support for the promotion of this technique.