Basement Tanking Strategies

[Backcheckrage]

I am doing some prelims on a fairly large basement carpark in a high seismic, high water table site. The excavation depth is something like 3.5m below grade. The water table is like 1m below ground, so 2.5m submerged the basement will ultimately be. The footprint is something like 1000m2. Some key design aspects I have highlighted are:

-sheet piling around perimeter to retain soil during construction
-screw piles to hold down the slab and walls for uplift buoyancy pressures. These will be strapped together with large grade beams over pile caps.
-precast walls around basement, typical
-treamie slab which is a working surface and won't be structural.
-steel and concrete "lid" over the basement.
-additional piles under shearwalls or braced frames.

One of the biggest things that bugs me is the waterproofing for this. I don't think it will be a good idea to de-water this thing while in service, so i'm proposing a bentonite system around the entire perimeter and underneath the slab. How the bentonite works seems a little voodoo to me. It's magical. Has anyone here used the product before? And how do they deal with bentonite around piles?

The product reps will always overpromise and overhype their product...

Any previous experiences will help!

 

[JedClampett]

I've never used bentonite. It has the reputation (maybe not deserved) for swelling once, and if it dries out, not rebounding. But it seems to be still really popular as a liner for ponds and the like.
But I think you're fighting a losing battle. Whatever waterproofing you apply, if it works, it's great, and if it doesn't, the sales guy is either nowhere to be found, or bravely blames the applicator. I'd suggest an active waterproofing system with perforated drains and sumps. Or put a trench around the perimeter and drain to a sump. It's only cars, they can get a little wet, especially if the water is only on he slab.

 

[hokie66]

I would look at a sheet applied or liquid applied membrane. You would have to apply it to the sheet piling and to the working slab. Then a protection layer such as fibre cement sheets on the slab. There may be protection material you can place to suit the sheet pile profile. Your waterproofing contractor and/or supplier may have preferable details to deal with the penetrations of the membrane at the columns and precast panels. I assume the precast panels will start on the structural slab, with perhaps a setdown for the panels which will serve to take the thrust at the bottom. The annular joint between the piling and precast will need to be filled to prevent displacement of the waterproofing by hydrostatic pressure from the rear.