The Mechanism And Application Of The Goaf Grouting With High Addition Fly Ash In Coal Mine

Based on the analysis of previous research results, the mechanism and application of the goaf grouting with high addition fly ash have been studied in this paper through simulation experiments, discrete element numerical computation, and field test based on the theoretical analysis and so on.Grouting material is one of the key parts of the grouting technique. The material properties directly influence the engineering quality, and the engineering input is also decided by the material price. For further study of the property of high addition fly ash-cement grouting material, the material properties under different parameter conditions were compared and analyzed based on the mix design of raw material in the laboratory. The results indicated that the water-solid ratio and the mixing amount of the accelerator have significant effect on the setting time, compressive strength, fluidity, and the stone rate of the grouting material. Meanwhile, ESEM analysis technique was used for the qualitative analysis of the morphology of the hydration products generated in systems and the active excited state of fly ash, combined with XRD technique, which analyzed the composition of the hydration products based on the crystal structure and changes in the peak intensity. MIP technique was utilized for analyzing different pore structure of grouting material, and the result explained its macroscopic impact on the physical and mechanical properties. The electrical property analysis of grouting material that should have no destruction on the material can be a scientific and feasible technical mean.Furthermore, in order to study the seepage characteristics of the grouting material in the old goaf, the simulation research was conducted by the physical simulation experiment of the plane stress. It has been suggested that the distribution of the slurry seepage trace depends on the characteristics of the pore distribution. In detail, the distribution of the slurry seepage trace presents spine shape in the caving zone of the old goaf, where gangue accumulated regularly, however, the slurry seepage trace distribution presents reticular structure in the caving zone with unregular gangue accumulation. Based on the analysis of the distribution of the slurry seepage trace, it has been found that there is obvious repression effect during the grouting slurry flowing through the gangue pores in the goaf due to integrated factors, such as the uncoordinated water-solid penetration of the slurry, electrolysis of the mineral salt contained in the fly ash-cement grouting material and the gangue pores. Moreover, once the slurry becomes grouting soil through different slurry seepage trace distributions, it has already changed the morphology of the gangue accumulation body, and improved the integrity and the strength of the medium.The study of the grouting material properties and the seepage characteristics has made preparation for further optimizing the grouting parameters. Theoretical model of the plane stress and the discrete element analysis software that is UDEC3.1 two-dimensional numerical simulation were used for the optimization analysis of three different parameters, including the grouting pressure, water cement ratio, and the solid phase ratio. The analysis result indicated that grouting pressure is the most significant parameter influencing the grouting effect, followed by water cement ratio, and the solid phase ratio is the last one. Specifically, if the grouting pressure value is 1.0MPa, the water cement ratio is in the range of 1:1.2～1:1.4, and the solid phase is 3:7, the grouting effect can achieve a relatively good level.This paper also proposed the goaf medium cooperation support system that is composed by the grouting soil, gangue and rock beam. Based on the schematic diagram of the goaf medium cooperation support system, the analysis of the goaf medium mechanical mechanism, and the stable conditions of the medium cooperation support system, it has been found that the grouting soil formed during the grouting process has lateral restraint upon the gangue and vertical supporting role to the overlying strata, which are the key parts to ensure the stability of the entire cooperation support system.On the basis of the experimental research and theoretical analysis, goaf grouting was conducted in the coal preparation plant of Antai. The practice results indicated that the grouting slurry seepage expressed good performance, the grouting soil formed after reinforcing effect has improved the gangue integrity, even optimized the stress environment and the carrying capacity. The field trials have achieved good effects.