Hi all, I have a question about retaining wall base preparation. I understand the process thoroughly for normal conditions, and for walls under 4' high. What I am unsure of is how freeze / thaw affects the sub base soil for a retaining wall. I understand that we are to install 6-10 inches of crushed limestone (compacted in 2" lifts) for the base, then use sand to level the base course. So the excavation would need to be done 10 or so inches below where you want the base course to lie. Here's my question - here in Western Maryland the frost line is at or around 3 feet below ground. So, unless you dig down 3 feet the soils below your base (6-10" of crushed limestone) are prone to freezing and thawing. So would this not make your base vulnerable to heaving and settling? Shouldn't we be excavating and installing base material 36 inches in my area? I haven't yet had a chance to go to the NCMA certification course, or else I'd already know the answer to this question. I'll be going before spring for sure.