Originally Posted by
threeighteen
Closer to ~16 inches.
There's obviously a softer base underneath that, but not really a requirement for a single landing and maybe a departure.
The ~16" thickness is so that the runway doesn't have to be replaced so often. You could go much much thinner for a one-time use.
I've seen runways under construction, much deeper than 16 inches. True you could use a thinner runway but only up to a point...a big airplane would break through if it's too thin.