Research on the Roof Advanced Breaking Position and Influences of Large Mining Height Working Face in Shallow Coal Seam

Abstract

The large mining height (LMH) in shallow coal seam has been widely applied in the Shenfu coalfield, China. The dynamic load is obvious, and the rib spalling is serious when the LMH working face concerns roof weighting. The advanced breaking position of the roof affects the strength of the ground pressure when the roof is broken. Firstly, based on a large number of actual measurements and physical simulation experiments, the rock formation in the fall zone, where the articulated structure cannot be articulated between the coal seam and the main roof, is called the equivalent immediate roof (EIR). When the mining height increases, the thickness of the EIR increases non-linearly. Next, based on the theory of “elastic foundation beam”, a mechanical model for the advanced breaking of the roof is established in shallow coal seam, and the calculation equation for the advanced breaking position of the roof is given; then, designed and carry out boreholes of the no. 22201 working face in the Zhangjiamao Coal Mine. The theoretical calculation of key strata results (5.6–6.9 m) are in the range of field measurement results (5–8 m). According to the field measurement results, the roof movement of the LMH working face is ahead of the roof weighting. Finally, we define the thickness of EIR and the mining height ratio as the immediate mining ratio ki, which affects the degree of filling of the goaf and determines the structural form of the main roof. When the ki is small, the goaf is fully filled; when the ki is large, the goaf is fully filled. Under the same conditions, different filling rate conditions will form different roof structures. Results of this research can be helpful to control roof weighting and provide early warning of possible safety problems related to the LMH working face in shallow coal seam.

Case Study on the Mechanism of Influence of Stoppage on Ground Pressure under Different Rates of Advance

“…However, when the rate of advance is decelerated due to special reasons, secondary unloading will occur. For this reason, some scholars have proposed a time transfer factor KT [21][22][23][24][25], as given by the following:…”

Analysis and control of the mechanism of coal pillar sloughing in the shallow buried thick coal seam

“…However, the coal seam thickness in the northwest mining areas in China is generally large and the geological structures, such as overlying strata are similar. 6,7 Therefore, it is urgent to study the sloughing mechanism and control of coal pillars in the thick coal seam, which provides the basis for underground safety production.…”

“…In the process of fully mechanized mining in large mining heights and thick coal seams, the stability of coal pillar and mechanism sloughing cause huge security risks to mine safety production, 3,4,5 transition supported to bring great economic burden to mine production. However, the coal seam thickness in the northwest mining areas in China is generally large and the geological structures, such as overlying strata are similar 6,7 . Therefore, it is urgent to study the sloughing mechanism and control of coal pillars in the thick coal seam, which provides the basis for underground safety production.…”

The Influence of Overburden Structure on Mine Ground Pressure Appearance in Working Face with Super-large Mining Height: a Case Study in Shendong Mining Area

“…In recent years, many experts and scholars have studied the law of M GPA and overburden structure of the super-high working face. Huang et al [9] studied the roof advanced breaking position and influences of large mining height working face in the shallow coal seam. Their research results can provide early warn ing for safety problems related to the large height working face of the shallow coal seam, but there is still no clear conclusion for the existence of multip le key strata in overly ing strata [9].…”

“…Huang et al [9] studied the roof advanced breaking position and influences of large mining height working face in the shallow coal seam. Their research results can provide early warn ing for safety problems related to the large height working face of the shallow coal seam, but there is still no clear conclusion for the existence of multip le key strata in overly ing strata [9]. Ju et al [10] summarized the law of M GPA in different mining stages of the world's first 7 m supporting working face and concluded that the distance between a single key stratum and coal seam was the main factor affecting the mining pressure; but did not quantify the factor.…”