You are spotting for a pipe crew that is laying 450mm diameter concrete pipe. The trench is 3 meters deep, and the pipe sections are 2.5 meters long. To maintain safety for workers in the trench, what minimum amount of cover should be placed over the pipe BEFORE heavy compaction equipment (e.g. walk-behind vibratory plate compactor used by hand) is used directly above the pipe?

Question: You are spotting for a pipe crew that is laying 450mm diameter concrete pipe. The trench is 3 meters deep, and the pipe sections are 2.5 meters long. To maintain safety for workers in the trench, what minimum amount of cover should be placed over the pipe BEFORE heavy compaction equipment (e.g. walk-behind vibratory plate compactor used by hand) is used directly above the pipe?

Answer options:

• 150 mm ✅ 300 mm
• 450 mm
• 600 mm

Correct answer: 300 mm

Explanation: A common site practice for protecting buried pipes, especially concrete, during backfilling is to ensure a minimum of 300 mm (12 inches) of compacted granular cover material over the pipe before heavier compaction equipment passes directly over it. This minimizes concentrated stress and potential damage from dynamic loads. For highly sensitive pipes, this depth may increase to 600mm.