A Computing Method for Sand Inrush Quantity through a Borehole in Longde Coal Mine

Table 5

Roughness height and angle of borehole [34–37].

	Rock type	Roughness height (mm)	Roughness angle (°)
Seol et al.	Gneiss	1–7	1.1–8.0
Seidel and Collingwood	Claystone, sandstone	1.7–16.2	1.9–18.9
	Shale, limestone, etc.	0.9–6.6	1.0–7.6
Lee et al.	Granite, Gneiss	1–4	1.1–4.6
	Sandstone, andesite	1–3.5	1.1–4.0
Nam	Claystone	3.6–5.3	4.1–6.1
	Limestone	3.2–3.7	3.7–4.2