Research on the Influence of Slurry Filling on the Stability of Floor Coal Pillars during Mining above the Room-and-Pillar Goaf: A Case Study

Abstract

Room-and-pillar mining is a commonly used mining method in previous practice in northwest China mining area. Due to priority selection of high-quality resources, coal mines in northwest China generally have to face upward mining above goaf. Thus, the stability of a floor coal pillar influenced by mining activities plays an essential role in upward mining above goaf. The results indicated that a floor coal pillar kept stable before coal excavation in the no. 6107 working face in the Yuanbaowan coal mine; however, the plastic zone in the floor coal pillar expanded sharply and the elastic core zone reduced suddenly on the influence of abutment pressure. Finally, the floor coal pillar supported failure. Accordingly, the paper proposed a floor coal pillar reinforcing technique through a grout injection filling goaf area. As physically limited by a different-height filling body on the double sides, the plastic zone scope and horizontal displacement and loading capacity of the floor coal pillar were studied, working out that the critical height of the filling body should be about 6 m which can ensure safe mining when upward mining above goaf. Case practice indicated that the fractures induced by mining in the floor coal pillar, filling body, and floor can be restrained effectively when the filling body height is 6 m, which can ensure floor coal pillar stability and safe mining of the no. 6107 working face in the Yuanbaowan coal mine. The research can provide theoretical and technical guidance for upward mining above goaf and have a critical engineering practice value.

Quantitative Evaluation of Isolated Overburden Grout Injection Technology Based on Large-Deflection Inclined Thin Plate Combined with Slurry Modeling

“…The overall work done on the thin plate bending by the stress released by the slurry on the PKS is: slurry 4…”

A New Method for Identifying Coal Pillar Instability Based on Energy and Stress Correlation Characteristics and Its Engineering Application

“…However, the distinction of which coal pillar in the coal pillar cluster is the first to fail and lose stability is still based on the distinguishing index of single coal pillar instability, such as the ultimate strength [31][32][33] and plastic zone proportion ratio [34][35][36]. The variation law of internal stress and energy of each coal pillar in the whole process from local damage, crack extension, and the main crack penetration to the overall failure has not been considered under the action of mining stress disturbance in the adjacent coal seam.…”

“…The variation law of internal stress and energy of each coal pillar in the whole process from local damage, crack extension, and the main crack penetration to the overall failure has not been considered under the action of mining stress disturbance in the adjacent coal seam. More importantly, in numerical simulation, a large amount of literature has adopted the distribution range or ratio of plastic zones to distinguish the stability of coal pillars [34][35][36], i.e., the coal pillar is considered to be destabilized when the ratio of plastic deformation units to the total number of units in the coal pillar exceeds a critical value. However, the concrete value of this critical value is often obtained empirically, such as 69% in the literature [23,36], as well as other works taking the width of the elastic core of the coal pillar to be no less than two times the mining height as the critical condition for instability [29,37], or some works taking the connectivity of the plastic zone as the criterion of coal pillar instability [38].…”

“…More importantly, in numerical simulation, a large amount of literature has adopted the distribution range or ratio of plastic zones to distinguish the stability of coal pillars [34][35][36], i.e., the coal pillar is considered to be destabilized when the ratio of plastic deformation units to the total number of units in the coal pillar exceeds a critical value. However, the concrete value of this critical value is often obtained empirically, such as 69% in the literature [23,36], as well as other works taking the width of the elastic core of the coal pillar to be no less than two times the mining height as the critical condition for instability [29,37], or some works taking the connectivity of the plastic zone as the criterion of coal pillar instability [38]. Numerous and highly diverse indexes make it difficult to accurately distinguish whether a single pillar is destabilized or not and to distinguish the first pillar to be destabilized in a multi-pillar system.…”

Isolated Overburden Grout Injection Technology Mining and Grouting Parameters Discussion and Redesign

“…solid lling [5,7], paste lling [8,9], and slurry lling [10]. Bed-separation lling mining refers to introducing ller material into a cavity, primarily via the Isolated Overburden Grout Injection Technology.…”