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Foam Styrene Backfill[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Foam Styrene Backfill
- From: Jim Warne <jwarne(--nospam--at)direct.ca>
- Date: Mon, 19 Oct 1998 21:53:14 -0700
I designed two of the grade separation bridges on the approaches to the Alex Fraser Bridge in Vancouver, in the mid - eighties. The subsoil was pretty soft, so most of the highway used encapsulated hog fuel (plastic wrapped bark mulch) in the roadbed to save weight and reduce settlement. At the retaining wall - style abutments for the interchange bridges, "beadboard" a.k.a. foamed polystyrene blocks, were used as fill for the last 20 feet or so against the abutment wall. It was a British Columbia Ministry of Transportation (Highways Department) choice. I'm not sure whether they were the innovators, but Styrofoam insulation has been used under roads in the Arctic for many years. I haven't heard of any problems with the foam under the bridge approaches. I look for signs of settlement whenever I drive over the bridges, and don't feel any bumps. Dow has lots of technical information on the use of Styrofoam for foundation insulation. I also designed a small garage addition where foam foundations were used, a few years ago. It was a site with silty, peatey soil, where the owner didn't want to use piles. There was concern about vibration damage to neighbouring property from pile driving. We used a somewhat dense beadboard, in the form of blocks, under a concrete slab with stiffening beams. It was a true raft foundation, in that we excavated enough subsoil material to balance the weight of the building. Again, the foam manufacturer provided information on structural properties. Creep was a concern with low density foams. As it was an auto service use, we placed polyethylene film around the perimeter, under the landscaping, to reduce oil movement under the building. The concrete slab ribs probably were enough to protect the styrene foam, but the film didn't cost much. Polyethylene has fairly good resistance to oil, as I recall.from my enquiries at the time. To answer the inquiry: plastic foam could probably be used against a retaining wall to reduce soil pressure and pprovide insulation. It will be more expensive than pea gravel. Jim Warne Vancouver, British Columbia jwarne(--nospam--at)direct.ca
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