The Study of Key Stratum Location and Characteristics on the Mining of Extremely Thick Coal Seam under Goaf

Gaochuan Guo,Yongkang Yang,Fengqiang Gong

doi:10.1155/2021/8833822

Gaochuan Guo, Yongkang Yang + Show 1 more

Open Access

https://doi.org/10.1155/2021/8833822

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Abstract

The basis of traditional ground pressure and strata control techniques is the key strata theory, wherein the position of the key stratum can easily be determined for coal seams with regular thickness and without goaf. However, in the case of mining ultrathick coal seams underneath goaf, the traditional methods used for the calculation of key stratum position need to be improved in order to account for the additional coal seam thickness and the presence of an upper goaf. This study analyzed the failure height and collapse characteristics of overlying strata during excavation for determining the structure of the failed overlying strata. The results indicate that the intercalation and overlying strata gradually evolve into a large “arch structure” and a small “arch structure” during longwall mining, respectively. A mechanical model of the bearing characteristics of the interlayer key strata structure was established according to the structure of the intercalation rock layer, which is a hinged block structure. The results of the model indicate that the maximum principal stress occurs when the key strata portion of the arch structure bears the overlying load. Consequently, the movement and position of the interlayer key strata can be evaluated throughout the mining process of the ultrathick coal seams underneath goaf. This method was used to determine the position of interlayer key stratum of overlying strata in Xiegou coal mine. And the results agree with that of the engineering practice. The results are significant to determine the key strata position during ultrathick coal seam underneath goaf longwall mining.

Highlights

Rock masses are in equilibrium stress states prior to excavation operations [1,2,3]; afterwards, the redistribution of internal stress occurs until a new equilibrium is attained as a result of the above disruption to the stress states of the rock masses [4,5,6,7]. roughout the excavation process, the overlying strata undergo varying degrees of deformation, movement, and destruction that can significantly impact the safety and efficiency of the mining operation [8,9,10,11]
Qian et al [16,17,18] developed the key stratum theory, which provides a theoretical basis for mine pressure appearance and overlying strata control as well as for the field of mine pressure control [13]
In the key stratum theory, the failure of a key stratum, which is defined as the stratum that controls the movement of the whole or a portion of the overlying strata, will cause the simultaneous subsidence of a portion or the entire overlying strata

Summary

Introduction

Rock masses are in equilibrium stress states prior to excavation operations [1,2,3]; afterwards, the redistribution of internal stress occurs until a new equilibrium is attained as a result of the above disruption to the stress states of the rock masses [4,5,6,7]. roughout the excavation process, the overlying strata undergo varying degrees of deformation, movement, and destruction that can significantly impact the safety and efficiency of the mining operation [8,9,10,11]. A mechanical model of the interlayer key stratum structure is established, and the movement periods of the key strata in the thick coal seam underneath goaf are determined. E damage height reaches the upper boundary of the model, and the hydraulic support is in the “given deformation” state, i.e., the separation of the immediate roof and the main roof occurred, and the support only bears all the weight of the rock strata collapsed by the immediate roof (Figure 2(e)); when the working face advances 180 m, the overburden is completely collapsed, the overlaying strata form a large “arch structure,” and the hydraulic support is in a “given load” state; that is, the load and deformation of the support depend on the interaction of the lower rock block in the regular. When the interlayer rock thickness is 35 m, it can be observed that the interlayer rock layer and the overlying strata gradually evolve from a small “arch structure” into a large “arch structure” as the working face advances, and the interlayer rock layer is an articulated block structure

Interlayer Key Stratum Judgment Criteria

Periodic Weighting of Composite Key Strata and Main

Field Application

Conclusions