I would like to install an allan block retaining wall (3' at its highest). I'm going to build a shop 25' downhill from this retaining wall, and want to have a poured slab for parking vehicles on. In researching foundations, it is recommended not to use a concrete foundation, so how to I ensure that there is not excessive water traveling under to the slab? the drain will prevent the water table from exceeding the drains height locally, but the soils below could still be fully saturated. Or is this OK?
As a 2nd question, how should I interface the gravel footer of the retaining wall and the driveway apron's slab? (Red question mark area in figure)
Lastly, why does allan block recommend a 4" x 18" wide footer? it seems the excess width provides no value, unless it is to ensure a plate compactor has the space get good compaction in the gravel.
Located in Zone 4C (Seattle area)