Deformation And Failure Of Overburden And Paste Backfill Due To Multiple Slices Backfill Mining

The coal measures in the Taiping Coalmine in Shandong province is covered by the Neogene unconsolidated layers, which has an average thickness of 158 m and an aquifer with medium water abundance occurrenced at the bottom of the Neogene System. The bedrock in the 6th district in the Taiping Coalmine has a thickness of 0~32.6m, which is classified as a thin bedrock. Then coal mining of panel S01 in the Taiping Coalmine belongs to the typical coal mining under thick unconsolidated aquifer and thin bedrock.Based on the experimental investigation and theoretical analysis, scale model testing and numerical simulation methods, the long-term mechanical properties and water stability of the paste backfill material, and the function mechanism of backfill during the process of filling mining were studied. Moreover, the overlying strata movement and deformation of backfill, the stress evolution of overburden and backfill were comparatively analyzed with intermittent filling in strip mining, longwall excavation and continuous filling. Then, the water stability criteria was established, and the efficient and rational mining scheme was proposed, which provides a theoretical basis for the mining practice. The main results are as follows:(1) The results show that the paste backfill material composed of SL cement, fly ash and sand has a high early strength, as well as the later strength, which can meet the needs of self-stabilization and post-filling body strength. The water stability of paste backfill material is moderate to strong according to the water stability criteria proposed in this paper. It is benefit to the paste backfill mining under water bodies with a strong softening properties and resistance to disintegration. Additionally, the backfill has little swelling, and the stable consolidation backfill with low permeability can be used as a relatively impermeable layer which is very favorable to mining under water bodies.(2) Research on the slicing filling mining with different mining scheme in the panel S01 of the Taiping Coalmine was carried out based on the use of scale model testing and numerical simulation methods, on the basis of the summarizing and analyzing of the backfill function mechanism and the filling effect influence factor during the paste backfill mining process. The results show that a most therious mining disturbance to the overlying strata by using caving mining in all the four slices, followed by using the caving mining in the first slice and backfill mining in the remaining three slices and continuous backfill mining in all the four slices. Morever, there has a weakest mining disturbance to the overlying strata and best surface subsidence control effect by using intermittent filling in strip mining in all the four slices.The equivalent mining thickness speculated from numerical simulation is basically in good agreement with the field test. Surface subsidence was effectively controlled as the good control effect of the roof- to- floor convergence and the gap between the backfill and roof in the Taiping Coalmine. Furthermore, the integrated consolidation backfill in the upper slice played a better role of impermeable protective layer for the next coal seam filling mining.(3) Combined with the project of similar mining results, when mining under thick unconsolidated aquifer and thin bedrock, only the second and third slices under the broken roof can be mined out with past backfill mining. The mining thickness and area should be strictly controlled when continuous backfill mining used in all the four slices. However, there has the maximum security in the stope with the intermittent filling in strip mining, as the effective suppress of overburden failure from the consolidation backfill in the last three slices which exert beneficial effects on the mining process of the fourth slice.