With all due respect, Joe, what we're planning is historically correct (edit: well, that deserves a caveat... See the end). The Wiscasset table had a timber retaining perimeter retaining wall for most of its life. The full perimeter concrete wall seen later on, and what is just below the surface of the ball field now, did not carry a ring rail. It was not rugged enough to add structure, and as far as we can tell wasn't even connected to the 'abutment,' where tracks ran on to the table. The structure of the foundation is in the center pour and the abutment pour, which we're planning on connecting with concrete ribs below the surface. If we truly want to reproduce what was in Wiscasset- what we're planning wouldn't change. We'd simply add a perimeter of either timber or thin concrete after the fact to keep the surrounding earth from slumping into the pit.
Remember this is not like most turntables we're used to seeing; queen truss tables gather their structure from above the table, meaning the pit is very shallow compared to a "modern" turntable pit.
Caveat: Note in the Facebook photo of Wiscasset's table, the timber wall is only maybe 8" tall; the only reason it was needed at all was because the track near one edge, and the hill below the school on the other side, prevented easy landscaping into the pit itself. So the Wiscasset table always had a retaining wall, but for most of its life it was timber, and it was only there for specific reasons.
See ya
Jason
