Quote:
Originally Posted by kw5150
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Quote:
Originally Posted by Aegis
What method do they use to shore up those walls?
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As a couple others have said, it's shotcrete shoring and it's all we seem to use in Vancouver.
The advantage of the technique is that you shore up the walls as soon as you can excavate and since there is no need for any pile driving it is very useful for tight urban sites. I am not familiar with the pile and wood plank system typically used in Calgary but from my observations in Vancouver the shoring operations seems to be pretty light on the labour front. In addition to the usual excavator and bulldozer teams that would be used no matter what, the shotcrete teams here seem to use between six and a dozen guys and depending on the size of the project multiple teams may be used simultaneously.
As a layman this is the process I have observed. First an excavator will begin clearing away soil in the centre of the site down and work their way over to the limit of the excavation pit. Then they excavate a fairly short section of soil wall and then a couple of guys running a self-propelled pneumatic drilling machine move in to sink and grout a steel anchor rod into the surrounding soil wall with a square end plate at the end. The excavator moves on to do the next section of wall while a small labour gang of half a dozen or so guys put up steel mesh rebar panels (picture something almost identical to those ubiquitous metal rental fences) by hand against the contours of the excavated soil wall. They finish by screwing a second end plate onto the anchor rod, sandwiching the steel mesh in between. Next a couple of guys run the shotcrete pumping machine that flings concrete from a ready-mix truck through a hose against the metal mesh, the bare earth wall behind, and the the anchor plates to create a relatively thick monolithic concrete wall that hugs the contours of the earth and seals in the rebar and anchor reinforcing assembly. Depending on soil conditions the initial excavation stage may require that buttresses of earth are left in an alternating pattern with the excavated sections to help give the earth wall additional support until the anchor, rebar, and shotcrete have been applied.The excavation and shoring process can be executed in quite a contained area and is linear in its progression so on a construction site you will see the whole operation corkscrews itself down to whatever depth is required. After the shotcrete shoring come a layer of impermeable membrane and then the actual building foundation and structural walls with backfilled rock in between.
I'm thrilled to see the West LRT continue apace. I can't wait until it's done. Good on you Calgary.