A trench for a 300 mm diameter utility pipe needs to be excavated in stable, cohesive soil to a depth of 2.5 metres. The provincial occupational health and safety regulations dictate that any trench deeper than 1.2 metres requires shoring or sloping. What is the minimum slope angle, relative to the horizontal, typically required for stable soil conditions to ensure worker safety without shoring?

Question: A trench for a 300 mm diameter utility pipe needs to be excavated in stable, cohesive soil to a depth of 2.5 metres. The provincial occupational health and safety regulations dictate that any trench deeper than 1.2 metres requires shoring or sloping. What is the minimum slope angle, relative to the horizontal, typically required for stable soil conditions to ensure worker safety without shoring?

Answer options:

• 1:1 (45 degrees) ✅ 1:2 (26.6 degrees)
• 1:0.5 (63.4 degrees)
• 2:1 (63.4 degrees)

Correct answer: 1:2 (26.6 degrees)

Explanation: For stable, cohesive soil, provincial regulations often allow for a maximum trench side slope of 1:2 (vertical to horizontal), which corresponds to approximately 26.6 degrees from the horizontal. A 1:1 slope is typically used for less stable soils or for general trenching guidelines, while steeper slopes like 1:0.5 or 2:1 are generally unsafe without significant shoring.