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Diameter (outer) tunnel

For rectangular tunnels, the outer diameter is calculated approximately using formula from Japanese Cable Standard JCS 0501. For circular tunnels, the outer diameter is the inner diameter plus the wall thickness.

The characteristic diameter of a trough is calculated as an equivalent diameter based on a formula by Huebscher, taken from engineeringtoolbox.com.

Symbol
$Do_t$
Unit
m
Formulas
$\sqrt{\frac{4\left(w_t+2t_t\right) \left(h_t+2t_t\right)}{\pi}}$tunnel rectangular shape (JCS standard)
$Di_t+2t_t$tunnel circular shape
$\frac{1.3\left(\left(h_t+t_t\right) \left(w_t+t_t\right)\right)^{0.625}}{\left(h_t+w_t+2t_t\right)^{0.25}}$trough equivalent diameter (Huebscher)
Related
$Di_t$
Diameter (inner) tunnel [m]
$h_t$
Height (inner) [m]
$\pi$
Archimedes' constant $\pi$
$t_t$
Thickness wall [m]
$w_t$
Width (inner) [m]
Used in
$T_{tw}$
Thermal resistance wall [K.m/W]