Owen Duffy wrote:

A conductor carrying RF currents and immersed in soil behaves like a lossy
transmission line. The bahavior depends on the parameters of the soil
(amongst other things), so the effect is different in dry sand than in wet
clay. Current entering the line will be attenuated along the line. . .

Please permit me to amplify on what Owen said, because it looks like it
might be interpreted. Burying coax in soil has no effect on the signal
inside the coax -- the loss of the coax transmission line isn't
increased. The lossy transmission line Owen refers to is the line made
up of the outside of the coax and, for the other conductor, the Earth.
This is the transmission line which carries the common mode current and
the one which will be made lossy by burying the coax.

Roy Lewallen, W7EL