# Tunnel/trough outer diameter

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
Formulae
 $\sqrt{\frac{4\left(w_t+2t_t\right) \left(h_t+2t_t\right)}{\pi}}$ tunnel with rectangular shape acc. JCS Standard $Di_t+2t_t$ tunnel with circular shape $\frac{1.3\left(\left(h_t+t_t\right) \left(w_t+t_t\right)\right)^{0.625}}{\left(h_t+w_t+2t_t\right)^{0.25}}$ equivalent diameter of a rectangular trough (Huebscher)
Related
$Di_t$
$h_t$
$t_t$
$w_t$
Used in
$T_{4d}$
$T_{tw}$