Heat transfer coefficient wall-soil

Assuming uniform temperatures at mudline and the outer surface of the pipe (i.e. Dirichlet boundary conditions), the heat transfer coefficient equivalent to the thermal resistance of the surrounding soil is commonly calculated from the following expression (Carslaw1959). This expression is appropriate for deeply buried pipes. When the top of line is close the soil surface (i.e. when the pipe is just barely buried), the heat transfer coefficient increases to infinity.

Symbol
$h_{soil}$
Unit
W/(K.m$^2$)
Formulae
$\frac{2 k_{4}}{D_{ext} \alpha_{0}}$
Used in
$D_{soil}$
$U_{buried}$