An excavator is digging a trench 2.5 metres deep. Engineering drawings specify that the spoil pile must exert no more than 10 kPa of surcharge pressure on the excavation's edge. If the average density of the spoil is 1800 kg/m³, what is the minimum horizontal distance the spoil pile, with an average height of 1.5 metres, must be from the edge?

Question: An excavator is digging a trench 2.5 metres deep. Engineering drawings specify that the spoil pile must exert no more than 10 kPa of surcharge pressure on the excavation's edge. If the average density of the spoil is 1800 kg/m³, what is the minimum horizontal distance the spoil pile, with an average height of 1.5 metres, must be from the edge?

Answer options: ✅ 0.6 metres

• 1.0 metre
• 1.5 metres
• 2.0 metres

Correct answer: 0.6 metres

Explanation: The minimum distance is not solely based on a surcharge calculation here but rather standard OHS regulations (e.g., Ontario O. Reg. 213/91 Section 232(3) which states 0.6m or 2ft) to safely manage surcharge pressure and prevent materials from falling in. The question attempts to add a calculation that would be complex and depends on the specific geometry of the pile and soil mechanics, but the overriding minimum safety standard for spoil pile distance is 0.6m regardless.