A Case Study on Gob-Side Entry Retaining Technology in the Deep Coal Mine of Xinjulong, China

Table 1

Table of coal seam roof and floor.

Name of strata	Name of rock	Thickness (m)	Lithologic description
Basic ceiling	Siltstone	2.30	Grayish black, horizontal bedding, upper homogeneous, lower with fine sandstone grain layer. Pyrrhotite film on lower layer. Vertical fissures developed, filled with pyrite and calcite, and the upper part contains abundant plant rhizomes and clastic fossils.
Direct top	Middle sandstone	17.80	Gray, thin layer, the main components are quartz, feldspar, particle sorting medium, subcircular, basal type muddy cementation, local development of siderite clams, layered distribution, forming vein-like bedding, vertical small fissures, filling pyrite film or calcite, and the core is relatively broken.
3 upper coal	—	2.45	Black, brown-black stripe, glass luster, mainly bright coal, secondary dark coal, containing more mirror coal, occasionally exists silk charcoal, belonging to semibright briquette. Endogenous fissures are extremely developed.
Gangue	Mudstone	1.45	Black, blocky, homogeneous, carbonaceous, flat fracture. Fracture development, filling pyrite and calcite. Rich in plant roots and leaf fossils, local carbonization.
	Fine sandstone	4.90	Gray, thin layer, rich in plant stem and leaf fossils and root fossils, common mirror coal strip and coal line, and oblique small cracks are seen and are filled with pyrite film or scattered crystal
	Mudstone	1.12	Black, horizontal bedding, flat fracture surface, uniform, coal clip, rich in plant stem and leaf fossils
3 lower coal	—	2.48	Black, brown-black stripe, glass luster, mainly bright coal, secondary dark coal, containing more mirror coal, occasionally exists silk charcoal, belonging to semibright briquette. Endogenous fissures are extremely developed and fragile. The bottom coal quality becomes worse. The gangue is carbonaceous mudstone and lumped.
		1.80
		0.27
Counterfeit	Sandy mudstone	2.00	Dark gray, homogeneous block, flat fracture, containing rhombic nodules, with vertical fractures, filled calcite, core broken.
Direct bottom	Fine sandstone	4.40	Gray, thin layer, even siltstone thin layer, develop slow wave-like bedding, and vein-like bedding and pyrite thin film are seen and scattered crystal on the bedding surface; the local particle size is slightly coarse, muddy inclusions or muddy stripes
Old age	Mudstone	1.30	Black, horizontal bedding, flat fracture, homogeneous, rich in plant stem and leaf fossils.