Waterproofing membrane under portal frame foundations and sliding
Waterproofing membrane under portal frame foundations and sliding
(OP)
I'm working on a project where the independent verifier has called into question the sliding resistance of one of our structures as our footings are on a waterproofing membrane. It is a portal frame type concrete structure on engineered fill with a friction angle of about 35 degrees.
Our engineer's calculations use tan(2/3)phi which basically means we're ignoring the waterproofing layer. The independent verifier is using a friction coefficient of about 0.25 because of the waterproofing layer.
My first thought was the if it moves any amount the membrane would be shredded anyway, but that argument falls over if waterproofing is required. Also if it moves the soil pressure will be relieved to Ka, but that's probably not going to help us either.
Does anyone know of any literature on the subject or how this is dealt with? I've been looking online but found nothing. We could just remove the waterproofing layer and use something like Xypex in the mix but I'd be interested to hear other points of view on this.
thanks
Our engineer's calculations use tan(2/3)phi which basically means we're ignoring the waterproofing layer. The independent verifier is using a friction coefficient of about 0.25 because of the waterproofing layer.
My first thought was the if it moves any amount the membrane would be shredded anyway, but that argument falls over if waterproofing is required. Also if it moves the soil pressure will be relieved to Ka, but that's probably not going to help us either.
Does anyone know of any literature on the subject or how this is dealt with? I've been looking online but found nothing. We could just remove the waterproofing layer and use something like Xypex in the mix but I'd be interested to hear other points of view on this.
thanks





RE: Waterproofing membrane under portal frame foundations and sliding
As for your question, if I were doing the calculations, I would use a very small coef. on the assumption that the membrane would last long enough for some movement to occur. So I guess I agree with the verifier.
Mike Lambert
RE: Waterproofing membrane under portal frame foundations and sliding
The water table is 30m below existing ground, we're surrounded by sand and it rains once a year. However I've been here in the middle east for 1 month and I've already learned to just accept some things.
RE: Waterproofing membrane under portal frame foundations and sliding
I would worry that Xypex would encounter the same issue. Unless it is a plastic membrane, they won't honor their warranty. You could call them and see if they would consider Xypex, but I'm guessing they won't ever give you an answer. If you don't have a architectural floor, you can eliminate the membrane. If you do, I'd just design for the reduced coefficient of friction, instead of removing the membrane. Another alternative is to take the chance of just eliminating it at footings, but that gets messy to specify and construct.
RE: Waterproofing membrane under portal frame foundations and sliding
i don't know how common it is but i have worked on a 200-bed psychiatric hospital designed by others that was fully encapsulated in poly like you describe. If you must use crystalline waterproofing to satisfy this requirement..... what you may want to do is have the foundation bearing soils approved, then cast a 4" mudmat, apply the xypex to that mudmat and cast concrete in forms. After stripping the forms you may come up the walls with almost any system (bituthene sheet, elastomeric, crystalline) if you're not really worried about it but need to address the requirement.... you could try mix design methods like adding Barrier-1.... you will always need to do the vapor barrier under the slab regardless.
RE: Waterproofing membrane under portal frame foundations and sliding
RE: Waterproofing membrane under portal frame foundations and sliding
Jed - there are no carpets. They are strip footings on a portal structure. They shouldn't need waterproofing but it's a project requirement - blanket statement for structural elements below ground level.
darthsoil - looking into a variety of things, thanks for the suggestions.
oldestguy - interesting, proof that this issue is worth looking into.