I am building a pit to hold some huge, uncommon, expensive machinary that is very interesting to discuss but of little importance to my question, so I will omit that info. Pit dimensions:

  • 12-20 ft deep

  • 50’ x 32’ L x W

  • wall thickness 16"

  • Slab depth 2’9"

The project is located in the East bay area and has a water table depth of 40’ according to the soils report. We are soil-nailing for shoring purposes and shotcrete-ing the walls to finished thickness. We would like to do this in one pass but will not be able to waterproof with traditional polyurethane membranes due to the soil nails. The only water mitigation will be a corrugated backing placed behing the shotcrete down full depth into a 12" layer of base rock.

My question is does anyone have any thoughts about how risky this would be to simply not waterproof other than the backing. And, does anyone know how well sodium bentonite or Integral crystalline waterproofing methods work?


Has someone designed this project for you? Sounds like a large and expensive project to be asking a message board for advice.

It mostly depends on if you have someplace for the water to go. Waterproofing doesn’t matter as much as drainage IMHO. Waterproofing can’t make a building into a boat. Does the water caught by the corrugated backing eventually gravity drain to daylight or somewhere? Or is the base rock a mote around the building?

I look at waterproofing as a plan B, only to be counted on to backup good drainage.

What I’m trying to say is that you can offset a lack of waterproofing with better drainage… so maybe back-filling with river rock higher than 12" would help.

I would plan for a pump just as a back up. The east bay is pretty good with the water table but what about when those heavy rains come once or twice a year? You could just plaster it and call it a pool. I have only seen one other person with the last name Frisbe. Got a relative named Ken?

a sump and a back up sump. perimeter drains to a “dry well”. This is the only way to guarantee a basement stays dry. I don’t see this any differently