Control of the Chamber in Extra-Thick Coal Seam Based on Fracture Characteristics of Coal Rock and Mass

Table 3

Characterization and rating of joint alteration factor J_A.

Classification of structural surface alteration properties	Description	JA
Local erosion and weathering exist on the structural surface, and the wall is closely contacted	Structural surface closed, no filling	0.75
	Fresh structural surface, no weathering	1.00
	Slightly weathered structural surface, with color infection on the wall	2.00
	The structure is intensively weathered with sand and silt on the wall	3.00
	The structural surface is altered and completely weathered, and the wall surface is covered with clay, kaolin, and other alternates	4.00
There are fillings between structural surfaces, and the wall surface is partially closed or not contacted	The structural planes are partially filled with sand and silt, and the walls are partially closed	4∼8
	The structural planes are filled with hard cohesive materials such as kaolin and clay, which are closely packed	6∼8
	The structural planes are filled with soft cohesive materials such as ultra-consolidated clay, which are closely packed	8∼12
	The structural planes are filled with expansive clay, which is closely filled	10∼18