Abstract
In order to effectively recover the residual coal resources, such as coal pillars and irregular coal blocks induced by large-scale extensive mining, in this study, we proposed a shortwall block mining (SBM) technology and examined the development pattern of the water-flowing fissure zone (WFZ) in the overlying strata during the SBM process. By analyzing the overlying rocks’ movement rules in SBM, the main controlling factors affecting the development of the height of the water-flowing fissure zone (HWFZ) determined are as follows: mining height, block length, and the width of the protective coal pillar among the blocks. Moreover, based on the elastic foundation beam theory, the mechanical model for the calculation of HWFZ in SBM was established. Based on the first strength theory, the calculation formula of the development HWFZ was derived. Using this model, the calculated HWFZ after SBM was 50.3 m, whereas the measured heights of the leakage of drilling washing fluid were 47.98 and 50.06 m, respectively. The calculated values almost fit well with the field-measured data, verifying the reliability of the proposed mechanical model. The results of this study can provide a significant reference for enhancing the recovery ratio of coal resources and optimizing water protection mining theory.
Highlights
Due to large-scale extensive mining and informal mining arrangements, a vast amount of residual coal resources, such as coal pillars and irregular coal bodies, have piled up after longwall mining for a long time [1–3]
The development height of the water-flowing fissure zone can be calculated by the thicknesses of various fractures strata: H = h1 + h2 + h3 + · · ·
In actual engineering we should first guarantee that the diversion fissure zone would not develop towards the aquifer; in order to enhance the coal column’s recovery ratio, the mining height and block length can be increased and the width of the protection coal pillar can be decreased
Summary
Due to large-scale extensive mining and informal mining arrangements, a vast amount of residual coal resources, such as coal pillars and irregular coal bodies, have piled up after longwall mining for a long time [1–3]. The recovery would inevitably cause the movement and destruction of the overlying rocks and form the water-flowing fissure zone (WFZ) [5], when the fissures develop aquifers and water-bearing regions on the surface, resulting in a loss of a great amount of water, depleting the water resource and affecting ecological environment. These adverse effects are serious in the mines in the arid and semi-arid Western China [6–13].
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