Retaining Wall on the Rear & West Side

The barn is surrounded by clay, and drainage is insufficient.  Silt washes down from the hill above and fills the small ditch I carved.  The barn has damp spots inside along the walls.  Here's the west side: muddy clay and a 3-4' banking, eroding & slumping:

We've hired a contractor to grade a better slope away from the barn and build a retaining wall to the side & rear.  I don't have confidence that I can establish a solid base for the retaining wall, so I hired an expert.  The contractor has an opening, so he's starting tomorrow AM, Labor Day.  Sunday night, various items are staged:  5 pallets concrete blocks, a couple tons of pulverized concrete, a couple tons (to start with) 3/4"- gravel; small backhoe, skid-steer with a bucket, and a trailer full of tools out on the road.

The pulverized concrete will provide a firm base, and as the wall grows, it will be used to fill the hollow blocks.

The gravel will go behind the wall, with a perforated pipe, to provide drainage from the slope above the barn.