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Now that we have looked in depth over three articles covering everything there is to know about shoring around an excavation, we going to back up one step this week and start back up at the surface; it's time to look at Backfill.
When a development is to be built on a site with a previous building on it, and that building had a basement, it typically leaves an unlevelled site. Even greenfield sites, with no previous building on them, can start this way too. Any tight site where an excavation is necessary is going to need shoring walls first, and putting those in, as we have learned, requires shoring rigs to move around the perimeter of the site to drill vertical shafts into the ground that soldier piles or caissons will be placed in. To drill those shafts properly, the shoring rigs need level ground upon which to work. Sites that aren't level, need therefore to be made level, and that typically requires backfill.
Backfill comes from other excavations. Once in place, shoring rigs can begin work, and once the shoring walls are ready, excavation can being, with the backfill, and much more from beneath the area that was levelled, being doug up and removed to a landfill site.
Some backfill may remain on site, however. Some of the aggregate may be required to be firmly packed around the perimeter of new foundation walls to increase stability or offering additional support to the foundation while protecting it from water damage that could lead to structural weaknesses. Other applications include landscaping or filling in voids that could potentially weaken underground structures. Since the earth is reused, backfilling is both practical and environmentally friendly.
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From 2015 to 2017, UrbanToronto and its sister publication, SkyriseCities, ran an occasional series of articles under the heading Explainer. Each one took a concept from Urban Planning, Architecture, Construction, or other topics that often wind up in our publications, and presented an in depth look at it. It's time to revisit (and update where necessary) those articles for readers who are unfamiliar with them. While you may already know what some of these terms mean, others may be new to you. We are publishing or updating and republishing Explainer on a weekly basis. This article is an update of one that first appeared in 2016.
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