Hi Bill,
I am surprised that you don't buy a pre-cast man-hole. A made-in-place manhole will likely cost you more $$. Is there anything special wrt the man-hole requirements? Is the site remote (ie transportation costs for a pre-cast manhole would be excessive).
Need additional info.
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)