I guess I’m the “Fred” to whom the question is being asked…
My experience up here in Ottawa, Ontario, Canada is based on all four distinct yearly seasons, with temperatures varying from -30C, to +30C.
We use trackage based on 2x PC lumber as roadbed, on the ground, and on benchwork varying from inches above ground, to a maximum of around 4 feet in height.
Over the 40 years of enjoying the running of trains; the benchwork has endured the tests of time very well, without major problems, but with expected areas that do experience the need of replacement after 20 years…or so.
The benchwork part of the railroad started out with “Legs” formed from 2x4’s, an 4x4’s. Both work well, depending on the area of benchwork, and its overall weight.
We have used what we call around here, “Deck Blocks”, (Pier Blocks) and in some cases we didn’t.
We have resisted against the use of “Posts in the ground” due to our usual frost in the ground problem. We have had no problems with any major frost heave, as long as we didn’t disturb the ground, and used 18" square patio stones to distribute the weight of the legs. As long as the patio stones are NOT layed level, moisture doesn’t get retained to wick up into the wooden legs.
We do use deck blocks, but find that they are not really needed, if the legs are properly braced, in fact they are better used if patio stones are put under them to spread the additional weight of the deck blocks.
Legs properly cross braced, as described by Bob Cope, partially avoid the need of the stability of the deck blocks. Any structure over 2 feet in height, with legs, should be cross braced for stability. The cost of simple 1x3, or 1x4 lumber is worth every dollar spent. With Deck Blocks, or without.
BTW…we have simple 2x4 legs, based on patio stones that have been in service for over 30 years…yes we did dip the bottom of the legs in wood preservative, right at the start !! “Properly cross braced”.
I hope this answers most questions. If anyone cares to chat on the subject, please feel free to call me, at: (613) 723-1911
Fred Mills