深埋弱胶结薄基岩厚煤层开采顶板动载冲击效应产生机制试验研究

doi:10.13722/j.cnki.jrme.2021.0340

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Abstract Mining pressure occurrence is strong in longwall faces of deep-buried thick coal seams with weakly consolidated thin bed rock. The compression and damage of hydraulic supports happen frequently due to dynamic loads resulted from roof failure. In order to improve surrounding rock control of such longwall faces，adopting laboratory experiment，theoretical analysis and in situ measurement，the occurrence mechanism of the dynamic impact effect is analyzed and the determination method of the dynamic load is discussed. The results show that mining-induced fractures initiate within upper alluvium in the referred longwall face，and that upward and downward propagations of the fractures respectively lead to collapse of the alluvium and rupture of the main roof，leading to the development of a caving arc in the overburden. If the caving arc undergoes local instability，the new caving arc presents an asymmetric shape. In this case，the main roof fails in tension，exerting a static load on the hydraulic support. If the caving arc shows integral instability，the new caving arc presents a symmetric shape. The main roof fails in shear，exerting a dynamic load on the hydraulic support. Downward propagation speed of the fractures is so fast that it penetrates the interface between the alluvium and the bed rock inertially. The main roof becomes a cantilever beam with inertial cracks at the top edge，seriously deteriorating the load-bearing capacity. The times required for the fracture propagating to the vault and the foot of the caving arc are consistent. Before caving of the alluvium，strain localization is highest at the initiation position of the fracture，followed by the arc foot and the arc vault. Instability of the caving arc leads to quick transition of the gravity load of the caving alluvium to the deteriorated cantilever beam，resulting in shear stress concentration at the inertial crack tip. Accordingly，shear failure happens to the main roof，and the strain energy stored in the main roof is transformed to be kinetic energy of the broken block. Non-statically initiated block impacts the bottom immediate roof and the hydraulic support，resulting in dynamic loads. The boundary function of the caving arc is determined with upper-bound theory，and the methods for calculating the load exerted on the main roof and the strain energy stored in the main roof are moreover put forward. After that，the initial speed of the broken block and the impacting force of the main roof are achieved based on energy and momentum conservation principles. At last，hydraulic fracturing is applied to 14030 face of Zhaogu 2nd coal mine to release the strain energy concentrated in the main roof，which helps to prevent the occurrence of dynamic impact phenomenon.

Key words： mining engineering weakly consolidated thin bed rock mining-induced fracture caving arc strain energy dynamic impact force

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	Articles by authors
	WANG Jiachen1
	2
	WANG Zhaohui1
	2
	TANG Yuesong1
	LI Meng1
	CHANG Kunlin1
	GONG Hao1
	XU Guoliang1

Cite this article:

WANG Jiachen1,2,WANG Zhaohui1, et al. Experimental study on mining-induced dynamic impact effect of main roofs in deeply buried thick coal seams with weakly consolidated thin bed rock[J]. , 2021, 40(12): 2377-2391.

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https://rockmech.whrsm.ac.cn/EN/10.13722/j.cnki.jrme.2021.0340 OR https://rockmech.whrsm.ac.cn/EN/Y2021/V40/I12/2377

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