Paste Backfilling Longwall Mining Technology for Thick Coal Seam Extraction under Buildings and above Confined Aquifers: A Case Study

Abstract

Backfill mining is an effective measure to control surface subsidence and restrain floor water inrush. It is an essential part of green mining technology. To solve the problem of confined water in mines under buildings, this study was carried out by combining theoretical analysis, laboratory simulation, and numerical simulation, taking the Liangbei coal mine as the research area. The coal seam floor failure characteristics of traditional longwall caving and paste filling mining methods were compared and analyzed. Based on the relevant mining theory, the key parameters, such as mining thickness and filling rate under the critical state of water inrush, were obtained. Then, the feasibility of backfill mining was expounded, and the surface subsidence of paste backfill mining was predicted and measured on site. The results demonstrated that the longwall caving mining method not only had the risk of water inrush, but also the possibility of step cracks at the surface, with the potential to result in serious damage to buildings. However, the backfill mining method reduced the floor damage depth of the coal seam from 12 m to 7 m, which reduced the water inrush coefficient by 12%, the maximum vertical concentrated stress by 42.1%, and the displacement subsidence value by 78.8%. These parameters correlated negatively with backfill strength. Meanwhile, the maximum subsidence, maximum inclined deformation, and horizontal displacement deformation were estimated as 730 mm, 2.5 mm/m, and 1.1 mm/m, respectively, consistent with the measured values (608 mm, 2.1 mm/m, and 0.9 mm/m, respectively). More relevantly, there were no obvious cracks found in the surface buildings, ensuring the safety of mining above confined water on the working face, and realizing the effective protection of surface buildings.

Movement and deformation characteristics of overlying stratum in paste composite filling stope

“…The dynamic change process of overlying stratum of PCFM is complex because the goaf is occupied by part of the paste filling body (Yang et al, 2021; Dudek and Tajduś, 2021; Wen et al, 2022). Compared with the caving method, the stope is affected by the filling body, and a new dynamic space of “support-surrounding rock (working face coal body, roof, floor)—composite filling body” is formed in the stope.…”

Evolution Characteristics of Overlying Strata Fractures in Paste Composite Filling Stope

“…Over recent years, paste filling technique has been widely applied for all mines, which can not only effectively control the stability of overlying strata and reduce the development degree of fracture zone, but also migrate strata behaviors and improve the stability of the "support-surrounding rock" system. It is one of the effective ways to thoroughly solve water-preserved mining problems [5][6][7][8][9].…”

Study on deformation control of overlying strata in short-wall coordinated filling mining of thick coal seam under aquifer

“…The recovery rate and safety of thick coal seam under aquifer are greatly improved by filling mining in layered roadway (Deng et al, 2017). Wen et al (2022) comparatively analyzed the traditional longwall mining and longwall paste filling mining of thick coal seam, and obtained the key parameters such as mining thickness and filling rate under the critical state of water inrush (Wen et al, 2022). Bai et al (2018) focused on the effect of backfilling mining under shallow thick coal seams on controlling groundwater loss and reducing surface subsidence, and obtained the optimal ratio of backfilling materials and slurry concentration (Bai et al, 2018).…”