Pit Greenhouse/walipini in Mid-Atlantic

Hi folks. Does anyone have experience building walipini in the mid-atlantic or northeast states? I'm in Virginia, which is considerably wetter than most of the arid examples of walipinis that I've found searching online.

Specifically, I'd like to know if anyone has found an effective way of dealing with:

Clay soil. What is the best way to work with the walls? We do not want walls crumbling over time, nor an excessive amount of moisture seeping in. We do want an earth floor for planting directly into, the walls however we would prefer more 'finished' to avoid any kind of degradation due to moisture and humidity in our area.

About 40 inches of rainfall annually. We need to figure out how to divert/channel this water to keep our walipini from flooding.

Thanks!

No, I don't have any idea.

I grew up in a place with heavy clay soil to the point where you had to dig with an adze.

No experience with inground green houses but I would make a retaining wall out of half rounds. put a perforated drain pipe in the bottom, and back fill it with course gravel or scoria. Then along the base of the wall, bury another perforated drainage hose in a trench filled with more gravel / scoria so it catches the run off.

Something like this:


Here is the link to where I found this image:
http://homes.msn.co.nz/diy/mitre10megadiyprojects/8405593/how-to-build-a-retaining-wall

Now that you've captured the water, put it to it's duties

Thanks Nick! That looks promising.