Field Measurement and Mechanical Analysis of Height of the Water Flowing Fracture Zone in Short-Wall Block Backfill Mining beneath the Aquifer: A Case Study in China

Abstract

Short-wall block filling mining (SBBM) technology has become an effective way to recover coal resources beneath the aquifer, which are unsuitable, or cannot be used by long-wall mining, such as corner coal pillars, industrial square pillars, and irregular coal blocks as well as the coal beneath buildings, railways, and water bodies. The SBBM method can not only enhance the recovery ratio but also provide a solution for the environment problems associated with gangues on the surface. However, whether the height of water flowing fractures will reach to the aquifer to cause water loss during SBBM has always been a key problem. Therefore, based on the theory of elastic foundation beam and SBBM characteristics, a mechanical model for calculating the height of a water flowing fracture zone in the overlying strata of SBBM was established, and this model calculated that the height of the water flowing fracture zone was 27.0 m in the experimental working face, and the height of the water flowing fracture zone was measured as 26.8 m according to washing fluid loss in the hole, core damage analysis, and drilling TV imaging detection. The comparison results demonstrated that the calculated value almost fit well with the field-measured data, validating the accuracy of the proposed mechanical model, while the predicted value (48.7 m) in the Regulations of coal mining under building, railways and water-bodies deviates greatly from the measured results. This reveals that the prediction formula in Regulations is not effective in predicting the height of the water flowing fracture zone in SBBM. The present research results are of great significance to further enhancing the recovery ratio of coal resources and improving the water-preserved mining theory.

Study on the damage characteristics of overburden of mining roof in deeply buried coal seam

“…After the workface mining, the overlying rock layer in the mining void area produces tension and pressure damage and forms mining fissures and sinks. The release of energy during the destruction of the surrounding rock in the mining fracture zone is the main source of mine pressure 21 . In the twenty-first century, microseismic monitoring technology is a newly emerged physical monitoring technology that has been successfully applied to early warning in several mine disasters, such as impact ground pressure monitoring, mine water damage control, gas extraction, and coal and gas protrusion in China.…”

Disastrous Mechanism of Water Burst by Karst Roof Channel in Rocky Desertification Mining Area in Southwest China

“…In terms of the development characteristics and laws of the water-conducting fractured zone, researchers represented by Liu Tianquan [8] have summarized and obtained the empirical formula for the development height of the waterconducting fractured zone through years of field research and analysis; Qiao et al [9] systematically summarized the research progress of aerosol water from four aspects, namely, the formation mechanism of roof aerosol water, disastercausing mechanism, water disaster prediction and early warning, and key prevention and control technologies; Yang and Xu [10] comprehensively employed the methods of theoretical analysis, similar material tests, and numerical simulation to obtain the evolution law of the water-conducting fracture zone in a large mining height face; Lai et al [11] used physical similar material simulation experiments, combined with the total station and borehole peep monitoring, 3DEC, and SPSS statistical analysis software, and obtained the migration law of overlying strata in coal seam mining, the development and evolution of fractures, and the distribution characteristics of water-conducting fracture zones; Zou et al [12] used FLAC3D software to calculate and analyze the plastic failure zone, displacement field, and stress field distribution characteristics of the surrounding rock above the stope before and after the fully mechanized caving work passes the fault and obtained the formation mechanism of the water channel; Wang et al [13] used theoretical analysis and field detection to obtain the characteristics of the development height of roof water-conducting fractures under the influence of the key layer structure with the mining thickness, and the development height is affected by both the mining thickness and the key layer structure; Zhang et al [14][15][16] used the theory of elastic foundation beams to establish a mechanical analysis model for the height of the overburden water-conducting fissure zone of the blockfilled stope; Zhu et al [17] built a coal seam mining model in the karst cave area and obtained the development characteristics of roof mining cracks during coal seam mining; Wang et al [18] used similarity simulation and theoretical analysis to propose a composite mechanism model of "elastic thin plate" and "parallel pressure arch" for the migration of overlying strata in high-strength mining under threedimensional spatial conditions; Liu et al [19] used the borehole television system and borehole simple hydrological observation method, combined with similarity simulation and numerical simulation, and obtained the development characteristics of the overlying water-conducting fissure zone in fully mechanized caving mining in deep and extrathick coal seams. In terms of the height of the waterconducting fissure zone, Y. P. Zhang et al [20] used a combination of field measurement, numerical simulation, and similarity simulation to obtain the overburden failure height of the deep thick coal seam in the west of Mongolia with the large mining height; Guo et al [21] used the method of onsite ground drillin...…”

A dual-continuum model (TOUGH2) for characterizing flow and discharge in a mechanically disrupted sandstone overburden

“…These overburden deformations also modify the hydrogeological setting of mined areas. Induced fractures, for instance, alter the flow paths of percolating groundwater while increasing the hydraulic conductivity of the rocks (Qu et al 2015;Zhang et al 2018b;Liu et al 2019;Qiao et al 2019). In addition, subsidence related to the deformation zone may change surface hydrological networks, increasing or decreasing the water balance of the mined area and changing the water level in the aquifers (Kelleher et al 1991;Blodgett and Kuipers 2002).…”