How deep can you dig without shoring?

STA 0+120Four ways to protect a trench

Every province's rules boil down to the same four tools, used alone or combined:

• Sloping. Cutting the trench walls back at an angle so they cannot collapse on a worker. The allowable angle depends on the soil type.
• Benching. Cutting the walls back in a series of steps rather than one continuous slope.
• Shoring. Timber, hydraulic or mechanical bracing installed against the trench walls to hold them in place. Alberta's Schedule 9 lumber-shoring tables, for example, cover trenches up to 6 m deep¹.
• A trench box (shield). A prefabricated steel or aluminum structure a worker stays inside of; it does not stop a collapse but protects the worker if one happens.

None of these are interchangeable by choice once a job is deep enough to need an engineer: past the thresholds below, the support has to be designed for that specific excavation, not picked off a generic chart.

STA 0+240Protection triggers by province

The table below pulls the trigger depth, the engineer-design threshold, the spoil or equipment setback and the ladder or safe-exit distance from each province's current excavation regulation. Where a fact was not confirmed in the current text of the regulation, the cell says so rather than guessing.

STA 0+360The number changes with the soil

Every threshold above assumes a worst case unless the soil is classified. Ontario and Saskatchewan both use a four-type system (Type 1 through Type 4, hardest to softest), and a mixed soil profile is classified as the highest-numbered (softest) type present⁵. The allowable slope tightens as the soil gets softer:

• Ontario: Type 1–3 soil can be sloped to within 1.2 m of the bottom at 1V:1H; Type 4 soil must be sloped from the bottom at 1V:3H⁵.
• Saskatchewan: Type 1–2 soil to within 1.2 m of the bottom at 1H:1V (45°); Type 4 soil from the bottom at 3H:1V (about 19°)³.
• Alberta uses a similar idea without the numbered types: hard, compact soil can be cut back to within 1.5 m of the bottom at not less than 30° from vertical; soil likely to crack, or soft and sandy soil, needs at least 45° from vertical¹.

None of this is something to eyeball. A soil that looks stable in dry weather can behave completely differently after rain, after a freeze-thaw cycle, or once vibration from a compactor or passing trucks starts working on the wall. Classifying soil correctly, and re-checking it if conditions change, is part of the job, not a one-time judgment call at the start of the day.

STA 0+480Extra rules near pipelines and buried utilities

The depth trigger is not the only number that matters. Several provinces add a proximity rule around buried lines, tighter than the general excavation setback:

• Alberta: mechanical excavation is not permitted within 600 mm of a buried pipeline unless the pipeline owner's representative is directly supervising, and any pipeline within 30 m of the work site must be located and marked before ground is disturbed¹¹.
• Saskatchewan and New Brunswick both require hand digging or an approved exposure method within 600 mm of a known line³⁷.
• Federally regulated pipelines: the prescribed no-dig-without-notice zone is 30 m on each side of the pipeline centreline, and a locate request has to go in at least three working days ahead¹¹¹¹.

This is why the sequence on every civil site puts locates before excavation, not after. See call before you dig for the one-call centre in each province, notice periods and what the paint colours mean.

STA 0+600When the job needs a professional engineer

Every province has a point where a generic shoring chart is not enough and a professional engineer has to design the support for that specific excavation. The trigger is usually depth (3 m in Alberta and Manitoba's open excavations, 6 m in Ontario, British Columbia and most Manitoba and Saskatchewan trenches), but Ontario is stricter for equipment: any prefabricated trench box or hydraulic shoring system needs an engineer's design regardless of how deep the trench is⁵. Quebec and the Atlantic provinces default the other way — an engineer's plans are the baseline requirement for any trench a worker enters, and sloping to within 1.2 m of the bottom without one is the exception, not the rule⁶.

Alberta carves out one more exception under section 449: sections 450 to 459 of the OHS Code do not apply at all if a professional engineer certifies that the ground formation is, and will remain, stable¹. That certification has to hold for the life of the excavation, not just the day it was issued.

Compare this against the underground utilities work covered in underground utilities and the volumes and slope math in the trench excavation calculator and the slope and grade converter.

STA 0+720Read the full rules for your province

The numbers above are the excavation-specific rules. Each province also layers on locate requirements, road-use rules and, for public work, prompt-payment timelines that affect how a trenching job gets scheduled and paid. Start with Alberta, Ontario or British Columbia for the fuller provincial picture, or the excavation cost guide for what a trenching job tends to cost once shoring, dewatering and traffic control are added in.