Spoil Pile Management

Written for Canada. Plans are metric, but many crews and suppliers work in feet and inches, so this site gives both: millimetres and metres, with feet and inches beside them. Codes are the National Building Code of Canada 2020 (NBC 2020) Part 9 as your province adopts it. A number marked Confirm has not been checked against every province, so check it with your own authority before you act on it.

Reviewed by a working tradesman with 17+ years in the field.

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Where the dug-out soil goes, how big the pile gets, and which way water runs around it.

The big idea

A pile of dirt next to a trench is a load sitting on the wall you are trying to keep standing. Where the pile goes, how big it gets and which way water runs around it all affect trench safety, your drainage, and whether you have clean material left for backfill.

Spoil setbacks come from your provincial OHS regulator, not from the building code, so they differ by province. NBC 2020 Part 9 sets no spoil setback.

How far back, and how much

• Where a pile sits next to a supported excavation, the shoring must be chosen to account for the extra side pressure from the pile.
• Alberta: spoil must be at least 1 m (3 ft 3 in) from the edge of the excavation to the leading edge of the pile, and the pile slope may not exceed 45 degrees from horizontal (OHS Code s. 453).
• Other provinces list distances close to this (see the By Province box). Treat 1 m as a floor, and go farther for deeper trenches and softer soil.

How tall will the pile be?

For a long pile with 45 degree sides (a windrow), the end view is a triangle with area h², so volume = h² × length. Example: 8 m³ of loose spoil in a 12 m (39 ft 4 in) windrow gives h² = 8 ÷ 12 = 0.667, so h = 0.82 m (2 ft 8 in), and the base is 2 × 0.82 = 1.63 m (5 ft 4 in) wide. With the nearest toe 1 m (3 ft 3 in) from the edge, the pile covers the ground from 1 m to 2.63 m (8 ft 8 in) back. Low and wide beats tall and narrow.

Where to put it

• On stable, level ground, well back from the edge and from any slope
• Away from ladders, walkways and the machine's travel path
• Away from existing structures, retaining walls and underground services
• Not where water naturally runs toward the hole
• Low and wide, with the sides at a stable angle

Water and spoil

• Do not let a pile dam a swale, block a drain or channel runoff into the trench
• Cover long-standing piles with poly or erosion blanket so rain does not turn them to mud
• Put silt fence or a straw wattle at the downhill toe of piles near drains or watercourses

Equipment

• Keep excavators, trucks and compactors off the edge. Machines load and vibrate the wall
• Never drive or park on a spoil pile next to a trench
• Never swing a bucket or load over workers
• Quebec's code keeps vehicles and machines 3 m (10 ft) from the rim unless the shoring is reinforced (summary). Check your own regulation for machines.

Keep your soils separate

• Strip topsoil and organics first and pile them on their own
• Keep clean granular material you plan to reuse apart from clay, silt and debris
• Set aside suspect or contaminated soil. Disposal of contaminated soil is regulated by the provinces
• Never mix organic soil back into bearing or backfill material

If you find something in the ground

Digging can uncover bones, stone tools or other archaeological material. Stop work at that spot, leave it as you found it, protect it and report it. Do not move it or keep it.

• BC: do not disturb a find. Contact the Archaeology Branch, 250-953-3334, Archaeology@gov.bc.ca. For possible human remains, contact the Branch immediately and do not disturb them; the Branch notifies the Coroner and local police. Archaeological sites are protected whether or not they are known, and a permit is required before altering one.
• AB: developers must report a find to the Heritage Division under s. 31 of the Historical Resources Act.
• Everywhere else: contact your provincial or territorial archaeology or heritage office, and the police if you think the find is human.

If the land is within First Nations territory, the Nation can also have an interest in the find, and your permit conditions may name who to call.

Common mistakes

• Piles right at the trench edge
• Tall, steep piles on soft ground
• Piles that block the ladder or the exit route
• Piles that send runoff into the hole
• Topsoil, clay and clean gravel all mixed in one heap