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.

Symbol
$Do_{\mathrm{t}}$
Unit
m
Formulae
 $2 \sqrt{\frac{1}{\pi} \left(h_{\mathrm{t}} + 2 t_{\mathrm{t}}\right) \left(2 t_{\mathrm{t}} + w_{\mathrm{t}}\right)}$ rectangular shape $Di_{\mathrm{t}} + 2 t_{\mathrm{t}}$ circular shape
Related
$Di_{\mathrm{t}}$
$h_{\mathrm{t}}$
$\pi$
$t_{\mathrm{t}}$
$w_{\mathrm{t}}$
Used in
$L_{\mathrm{deep}}$
$L_{\mathrm{psc}}$
$T_{\mathrm{tw}}$
$u$