It's looking like a wet stamp job

One of the bits of jargon I've picked up from talking with landscape contractors is "wet stamp design." This is a design, plan, or schematic that is known to be vetted and pre-approved by the local building & planning department. Using a wet stamp means you don't have to hire a structural engineer to create a custom design for the job, which saves money and time.

There is a seriously overengineered wet stamp CMU retaining wall design for the County of Marin that Novato approves of that looks to me like it could hold back a hill of mud. I didn't like it: it specs that a 4.5' wall needs a 4.5' wide base, with lots of rebar and a keyway (I'll try to post a drawing later). But after going through the custom design process for a poured concrete retaining wall with a geotech and a structural engineer, it turns out I practically do have a hill of mud to deal with.

Dry clay is rock hard, with a load bearing capacity of 8000 pounds per square foot (psf) or more. But wet clay is only 2000 psf and likes to slide. A design that will safely withstand the pressure of that wet clay is nearly as hefty as the wet stamp design. Since I don't have to pay for ~$1500 of engineering to use the wet stamp design, it's starting to look attractive.

I can put off a final decision for another week, since this weekend I'll be removing a massive eucalyptus stump for our hillside with chainsaw, 25hp self-propelled stump grinder, Bobcat (to build a ramp to the stump for the grinder) and excavator (to pull out the roots and ground up bits.) If I have time left over I'll start the excavation for the wall footing.

Here's David last weekend, having at the stump with the chainsaw to cut vertical grooves. It was my plan then to pull the stump apart at the grooves with the excavator. This was a complete failure, since the stump is massive, strong, and full of dirt that dulls the saw blade in seconds. The pros cut off the wood and grind up the stump.