I confess, for many years I determined that if I was ever going to start a new garden railroad, I would use exclusively 2"x6" raised railroad on posts. These are pretty "bulletproof" if they're installed properly (say with the posts below the frost line or any other adjustment your environment requires. The way folks do this is described here: https://www.familygardentrains.com/prim ... _posts.htm
I would also build retaining walls out of pressure-treated, ground-rated lumber, including buried posts and walls built out of 2"x6"s. One example of this construction, also very reliable, is shown here: https://familygardentrains.com/primer/w ... .htm#fence
Then we moved, and we left the old railroad, built partly this way, but mostly not, behind us. And I started designing the new railroad with those principles in mind. I realized quickly that I would be digging a LOT of post-holes. If I was JUST going to have a raised ROW, with, say, a trestle underneath it, the 2"x6" roadbed approach would still apply just fine. (I will still probably have a section made this way, in the future.)
But I wanted my towns and farms to be just as high as the track - or higher. And the only way to do that with a retaining wall/backfill approach would require a lot more post-holes just for the retaining wall. Plus a LOT of dirt being hauled in to get that height.
Also, I wanted to have ROWs on multiple levels, with the top one being 5' or so off the ground. And that would require a ridiculous amount of dirt, plus a ridiculous amount of lumber to support it.
In addition, having that much dirt in the past encouraged things like moles, voles, and ground squirrels to move in and disrupt the ROW. Not to mention weeds, weeds, weeds, and more weeds. The first problem was mitigated somewhat on the old railroad when I dug out a deep, wide channel under most of the ROW and poured crack-resistant concrete there. But every year seemed to be bringing a new species of invasive weeds that required constant vigilance to keep under any semblance of control.
To combat the latter problem, I considered using a sort of raised-planter arrangement, in which plants could only only grow PERIOD in certain areas.
Then I thought about another issue. I was going to be trying a bunch of new things, and I wanted to be flexible regarding track plans. If your ROW is on posts, tweaking your track plans can be a major issue, though.
So with the new list of requirements (based on 18 years of doing garden railroading the way most of the "Experts" were doing it back in 1998, it occurred to me that I could raise the ROW and the buildings and everything else faster, more economically, and frankly, more reliably if I skipped the "dirt pile" and retaining walls altogether, and just built a tabletop outside. Actually three tabletops, of which only two are going to be done this year.
The result is a multi-layered deck-like structure that I'm still building as I type this, but I have great hopes - especially since Home Depot has started making their 2"x6" pressure-treated lumber "ground-rated," which means they shouldn't rot out no matter how long they stay in contact with the dirt.
The story of my decision-making process and early attempts starts here:https://familygardentrains.com/newbost/ ... b_n_dc.htm
If you start at that article and work your way through to where I am today, you'll see how my thinking changed over time, and the result of those changes on my "final" design. Plus what at least part of it looks like built up at this moment.
No, it's not done, or even half-way done yet, nor will it be for a couple more years. But it's a start.
Please use the contact link on any of the article pages to let me know what you think.