We've talked about the importance of a strong foundation to a building's structural stability in past editions of Explainer, including measures like underpinning that aim to provide additional strength. The process of backfilling can also offer additional support to the foundation while protecting it from water damage that could lead to structural weaknesses. 

Digging up the old foundation at a site in Toronto, image by Marcus Mitanis

When a property is excavated, the compacted aggregate earth and stone that is removed is known as backfill. The aggregate can be firmly packed around the perimeter of foundation walls, thereby increasing stability. It can also be returned to the property in preparation for construction, creating a smooth site that provides a perfect surface for work to begin. 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. 

The same site after backfilling, image by Forum contributor G.L. 17

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