96
4 Mine Ventilation Networks
There is also a scale effect, i.e. a larger gallery has a smaller friction factor. This fact
is of particular relevance to small cross sections, as the coefficient grows potentially
as the cross section decreases. Therefore, when using old tables, it must be taken into
account that they were derived when the mining galleries were much smaller than
the present ones. Thus, values of two-thirds of those in the tables are closer to present
needs (de la Vergne 2008). For standardization purposes, many tables (e.g. Simode
1976; Carrasco et al. 2011) refer to sections of 10 m
2 (Table 4.2). If the gallery is
different from 10 m
2 , the values can be corrected using Eq. 4.12:
Table 4.2 Main friction coefficients. Modified from Simode (1976) and Carrasco et al. (2011)
Element
Coefficient of friction
Floor
f floor
Smooth (concrete)
0.025
Well trimmed
0.058
Regular
0.084
Irregular
0.108
Gallery wall
f wall
Bare rock
Well trimmed
0.058
Medium
0.084
Irregular
0.108
Bolted
Well trimmed
0.058
Medium
0.084
Irregular
0.108
Wire mesh
0.130
Coated
Smooth concrete
0.022
Brick lined
0.025–0.040
f x =
f 10
(0.75 + 0.25 log A)
2
(4.12)
where
• f x : Coefficient of friction for an airway of A cross section,
• f 10 : Coefficient of friction of an airway of 10 m
2 of cross section, and
• A: Cross-sectional area of the airway (m
2 ).
Note that while there is a simple connection between K 1.2 and f (0.15 f = K 1.2 ),
this is not the case for R 1.2 . This is so because, by definition R = K 1.2
O(L+L eq )
A 3
, and
therefore depends on geometric parameters of the gallery, such as the cross-sectional
area and the perimeter.
4 Mine Ventilation Networks
There is also a scale effect, i.e. a larger gallery has a smaller friction factor. This fact
is of particular relevance to small cross sections, as the coefficient grows potentially
as the cross section decreases. Therefore, when using old tables, it must be taken into
account that they were derived when the mining galleries were much smaller than
the present ones. Thus, values of two-thirds of those in the tables are closer to present
needs (de la Vergne 2008). For standardization purposes, many tables (e.g. Simode
1976; Carrasco et al. 2011) refer to sections of 10 m
2 (Table 4.2). If the gallery is
different from 10 m
2 , the values can be corrected using Eq. 4.12:
Table 4.2 Main friction coefficients. Modified from Simode (1976) and Carrasco et al. (2011)
Element
Coefficient of friction
Floor
f floor
Smooth (concrete)
0.025
Well trimmed
0.058
Regular
0.084
Irregular
0.108
Gallery wall
f wall
Bare rock
Well trimmed
0.058
Medium
0.084
Irregular
0.108
Bolted
Well trimmed
0.058
Medium
0.084
Irregular
0.108
Wire mesh
0.130
Coated
Smooth concrete
0.022
Brick lined
0.025–0.040
f x =
f 10
(0.75 + 0.25 log A)
2
(4.12)
where
• f x : Coefficient of friction for an airway of A cross section,
• f 10 : Coefficient of friction of an airway of 10 m
2 of cross section, and
• A: Cross-sectional area of the airway (m
2 ).
Note that while there is a simple connection between K 1.2 and f (0.15 f = K 1.2 ),
this is not the case for R 1.2 . This is so because, by definition R = K 1.2
O(L+L eq )
A 3
, and
therefore depends on geometric parameters of the gallery, such as the cross-sectional
area and the perimeter.