Study On Reducing Residual Settlement Of Overburden By Grouting Reinforcement In Old Goaf Of Longwall Mining

In recent years,with the rapid development of urbanization in China,the shortage of land resource utilization caused by the continuous expansion of urban area has become increasingly prominent,which forces some new buildings(structures)to be constructed and used across the area above the old goaf.Although the old goaf has been stabilized after a long time of natural compaction,it is easy to produce under the action of new ground load Secondary activation,so in order to ensure the normal and safe use of new buildings(structures),it is necessary to analyze and evaluate the stability of the foundation in the goaf of the proposed area,and take reasonable measures to control and strengthen the goaf.At present,grouting technology is widely used in the treatment of goaf,but it has strong practicality.During the construction of the project,it is mainly based on experience,and there are many researches on grouting materials,technology and equipment.However,the researches on grouting Subsidence Reduction Theory in goaf,pressure bearing characteristics of fractured rock mass before and after grouting,grouting simulation and effect evaluation are relatively insufficient Further improvement is needed.In this paper,through theoretical analysis,laboratory test,numerical simulation and other means,the mechanism of Subsidence Reduction by grouting reinforcement in goaf,the compaction characteristics before and after grouting of broken rock mass in goaf and the simulation of grouting reinforcement effect in goaf are studied.First of all,based on the analysis of the old goaf overburden structure,this paper summarizes the previous research on grouting theory,divides the goaf grouting area,summarizes the flow characteristics of the grouting area,proposes the goaf grouting reinforcement support system composed of gangue plus solid,gangue body and rock beam plus solid,and studies the mechanical mechanism of the coupling support system In order to ensure the groutability of the fly ash cement slurry and save the grouting cost to the greatest extent,the physical and mechanical parameters such as compressive strength,viscosity,setting time,stone rate of the fly ash cement slurry at different age under different proportioning conditions are obtained through the indoor slurry Proportioning Test,and the proportioning of the large amount of fly ash based slurry is optimized;the basis of the experimental study on the proportioning of the sluny is Based on the real triaxial test system of rock,the uniaxial side limit loading test is carried out in the self-made rigid compression cylinder for the broken rock with different initial particle size gradations in the natural state to study the compression deformation characteristics of the broken rock mass before and after grouting and carry out comparative analysis;according to the existing geological data of the goaf,the numerical simulation software FLAC3D is used to simulate the influence of the goaf only by the self weight to the grouting The results show that the deformation parameters of the surface residual deformation after grouting are significantly reduced compared with that before grouting.When the surface building load is applied to the model,the parameters of the surface residual deformation slightly increase compared with that after grouting,but the increase is smaller.It can be considered that the proposed area is basically stable after grouting It is suitable for the construction of the proposed buildings.