A trench is being excavated for a new water line in unstable, sandy soil. The trench is currently 2.5 metres deep. What is the required minimum distance that excavated material (spoil pile) must be kept from the edge of the trench?

Question: A trench is being excavated for a new water line in unstable, sandy soil. The trench is currently 2.5 metres deep. What is the required minimum distance that excavated material (spoil pile) must be kept from the edge of the trench?

Answer options: ✅ At least 1.0 metre from the edge of the trench.

• At least half the depth of the trench, so 1.25 metres.
• As far back as possible, but no less than 0.6 metres.
• Only enough to prevent it from falling back into the trench, typically 0.3 metres.

Correct answer: At least 1.0 metre from the edge of the trench.

Explanation: Excavated material (spoil pile) must be kept at least 1 metre (3 feet) back from the edge of the trench to prevent it from falling back in and to reduce the surcharge load on the trench walls, which can contribute to collapses, especially in unstable soil. Other distances stated are incorrect or inadequate for safety.