Multifactorial analysis of a gateroad stability at goaf interface during longwall coal mining – A case study

Abstract

Purpose. Creating a generalized algorithm to account for factors (coal seam thickness, enclosed rock mechanical properties, the dimension and bearing capacity of artificial support patterns) causing a gateroad state under the effect of longwall face and goaf. Methods. The assessment of the gateroad stability is based on numerical simulation of the rock stress-strain state (SSS). The finite element method is used to find out the changes in the SSS of surrounding rocks at various stages of longwall mining. The elastic-plastic constitutive model and Hoek-Brown failure criterion implemented in codes RS2 and RS3 (Rocscience) are applied to determine rock displacements dependently on the coal seam thickness, enclosed rock strength, width and strength of artificial support (a packwall comprised of hardening mixture “BI-lining”). To specify the mechanical properties of the packwall material a series of experimental tests were conducted. A computational experiment dealing with 81 combinations of affecting factors was carried out to estimate the roof slag and floor heaving in the gateroad behind the longwall face. A group method of data handling (GMDH ) is employed to generalize the relationships between rock displacements and affecting factors. Findings. The roof-to-floor closure in the gateroad has been determined at the intersection with the longwall face and goaf dependently on the coal seam thickness, enclosed rock strength, width of the packwall, and strength of hardening material. It is revealed that the support material gains the strength value of 30 MPa on the 3rd day from its beginning to use which is fully corresponding to the requirements of protective element bearing capacity. The possibility of using untreated mine water to liquefy the mixture is proved, that allows simplifying and optimizing the solute mixing and pumping technology. Originality. This study contributes to improving the understanding of the factors that influence the stability of underground mining operations and highlights the importance of utilizing numerical simulations in optimizing mining designs. The impact of each factor on the resulting variable (decrease in cross-section of gate road by height) based on the combinatorial algorithm of structural identification of the model is estimated as follows: the packwall width is 48%, the thickness of coal seam is 25%, the strength of enclosing rocks is 23%, and the strength of the packwall material is 4%. Practical implications. The findings provide stakeholders with a technique to determine reasonable parameters for support and protective systems, and the predictive model developed can be used to mitigate potential instability issues in longwall mining excavations. The results have implications under similar geological settings and can be valuable for mine design and optimization in other regions.

Analysis of Rock Burst Mechanism in Extra-Thick Coal Seam Controlled by Thrust Fault under Mining Disturbance

“…Prospecting line 41 is bound via the Qianqiu and Yuejin Mines to the east. The mining area is 11.503 km 2 .…”

“…Coal geological conditions and mining disturbances have an important influence on the stress distribution of a longwall face [1,2]. With the increase in coal mining depth, the geological conditions gradually deteriorate.…”

Quantitative Characterization and Disturbance Law of Key Parameters Influencing Deformation of Overlying Strata during Strip Filling in a Goaf

“…Consequently, the structural parameters of the mining site also play a crucial role in influencing surface subsidence and coal mining roof stability. Chi [14] determined the optimal structural parameters of strip filling stopes through orthogonal test simulations; Wang [15] conducted numerical simulation orthogonal calculations on roof stability under multiple factors' influence, obtaining the influence laws of various factors on roof tensile stress; Dong [16] achieved optimization decisions on the structural parameters of strip filling stopes by establishing an orthogonal numerical model; Guo [17] examined the sensitivity of coal seam dip angle, extraction width, extraction thickness, and filling rate to surface subsidence in strip filling mining; Dmytro [18] studied the stability of the roof and floor during longwall mining through numerical simulation and experimental testing, and the author identified various factors that affect the state of the roadway. Numerical simulation research on filling stopes based on orthogonal experimental design not only overcomes the shortcomings of overly idealized theoretical analyses but also conserves experimental costs.…”

Research on the Stability and Water Isolation of Waterproof Coal Pillars between Adjacent Working Faces under the Influence of Water Ponding Goaf—A Case Study

“…In addition, the calculation formula only considers the influence of coal seam thickness and water pressure on the size of coal pillars and ignores the influence of buried depth and coal strength on the size of coal pillars [15][16][17]. In the United States, the earliest known waterproof coal pillar calculation formula was proposed by Dunn in 1846 [18][19][20], which was calculated after a given depth, and thus, the calculated size of coal pillars is on the smaller side. Indian scholars have adopted the waterproof coal pillar calculation method of coal pillar strength and anti-slip force, taking into account the two conditions of stabilized mining areas and goaf, but the limitations of its applicability and the overly complex parameters of the formula make its application inconvenient.…”