Strata Movement and Mining-Induced Stress Identification for an Isolated Working Face Surrounded by Two Goafs

Abstract

Solutions for the maintenance of safety in an isolated working face has not been well achieved; this is attributed to its unique overburden structure and the strong mining-induced stress during the advancement. This paper is devoted to filling this research gap and is based on the case study of LW 10304 in the Xinglongzhuang Coal Mine, in China. The overburden structure and stress distribution characteristics of this isolated working face were theoretically investigated, followed by the development of a comprehensive identification method. The research results showed the following: (1) The overburden strata of LW 10304 is in the form of a short “T” shape and the stress increment is featured with the overall “saddle” shape before the extraction of the isolated working face. During this period, the lower key strata and main key strata affect the stress level at the two ends and the central part of the working face, respectively; (2) Both the frequency and energy of micro-earthquakes in the working face account for more than 95%, which is positively correlated with roof damage and rib spalling, associated with some overlaps between the damaged zones; (3) The fracture movement of inferior key strata near the coal seam plays a dominant role in affecting microseism activity and mining-induced stress. The microseism energy attributed to roof breakage accounts for 43.34% of the overall energy; (4) A comprehensive indexing system, covering microseism frequency, microseism energy, and support resistance, was established to identify the mining-induced stress intensity of the isolated working face. The early warning efficiency of the “strong” degree of mining-induced stress is 0.94, which is believed to provide an option for other isolated working faces with similar geological and mining conditions.

Exploring the Distribution Characteristics of High Static Load in the Island Working Face of Extra-Thick Coal Seams with Hard Roof: Addressing the Challenge of Rock Burst Risk

“…With the continuous mining of coal resources, coal mining conditions are becoming more and more complex. The geological structure division and the need for safe mining require the use of the jump mining method between working faces in the mining area, resulting in the formation of various types of island working faces [3][4][5]. Due to the continuous and complete structure of the overlying strata on an isolated island working face, the pressure on an island working face is greater than that on a non-island working face [6,7].…”

“…They also discovered the mechanism underlying a rock burst caused by an island working face's symmetrical long arm T-shaped structure [25]. Through the analysis of mining scale and settlement results, Wen et al concluded that the overlying low key strata of an island working face with the long-arm T-shape are mainly controlled the microseismic activity and mining stress response of the working face [4]. Based on the load transfer mechanism, Zhu et al derived a series of formulas for the average static stress and dynamic stress of island coal pillars through theoretical analysis [26].…”

Change Characteristics of the Advance Stress and Strata Fracture Structure of Spatial Isolated Island Formed by Roof Drainage

“…Wen et al [8] conducted a theoretical study on the overlying rock structure and stress distribution characteristics of the isolated island working face LW 10,304 of the Xinglongzhuang Coal Mine in China. They reported that prior to the mining of LW-10304, the overlying rock had a short "T" shape, and the stress increment was in the shape of a "saddle".…”