Excavation, Trenching, and Shoring
This domain tests the rules that keep people alive in and around excavations: locate first, protect the walls, control access, keep spoil back, and inspect constantly. Expect questions on depth thresholds, sloping, trench boxes, ladder spacing, atmospheric testing, and water.
Before you dig and while you dig
- Confirm locates, then hand expose services inside the tolerance zone.
- A competent person inspects the excavation at the start of each shift, after rain, after vibration, and whenever conditions change.
- Barricade and sign open excavations; provide safe crossings and keep equipment back from the edge.
Wall protection
- Most jurisdictions require wall protection once a trench reaches 1.2 m (4 ft) deep; confirm the depth threshold in the province you work in, as some use 1.5 m.
- Options are sloping, benching, shoring, or a trench box. Soil type, water, surcharge loads, and adjacent structures all affect the choice.
- Slope ratios depend on soil classification; a common minimum for firm soil is 1:1, but the provincial table governs.
- Trench boxes must be installed per the manufacturer, seated at or near the bottom (commonly within 600 mm), and never used to lift workers.
- Do not use excavated spoil to build a slope.
Access, atmosphere, and water
- Provide a ladder or ramp within 7.5 m (25 ft) of travel for every worker in a trench 1.2 m or deeper.
- Test the atmosphere where gas may accumulate, in deep trenches, and near utilities; ventilate if needed.
- Never work in standing water. Dewater with pumps and discharge through sediment control, not directly to a storm drain.
- Spoil and materials are kept back at least 1 m from the edge, with a larger setback for heavy equipment.
Worked example
A trench 2.4 m deep and 1.2 m wide is planned in firm clay beside a sidewalk, with no groundwater. Because depth exceeds the protection threshold, the crew chooses a trench box sized for the width. The box is set within 600 mm of the bottom, spoil is stockpiled 1 m back on the opposite side from the ladder, and a ladder is placed within 7.5 m of the work area. The competent person inspects at shift start and after each rain, and the atmosphere is tested before entry. The sidewalk is monitored for cracking and vibration because it is a surcharge load.
Traps that cost marks
- Entering for "just one quick look" without protection.
- Skipping the inspection after rain.
- Setting the ladder outside 7.5 m of travel distance.
- Assuming a trench box protects against everything, regardless of soil or surcharge.