An excavator operator is backfilling a foundation. The civil engineer requires the fill material to be placed in lifts of no more than 300 mm and compacted to 95% Modified Proctor density. What is the most effective excavator technique to achieve thin, consistent lifts before compaction?

Question: An excavator operator is backfilling a foundation. The civil engineer requires the fill material to be placed in lifts of no more than 300 mm and compacted to 95% Modified Proctor density. What is the most effective excavator technique to achieve thin, consistent lifts before compaction?

Answer options:

• Dumping large bucket loads randomly and spreading them with the bucket floor.
• Placing a full bucket load and dragging it horizontally across the area in a single wide sweep. ✅ Metering out smaller amounts of material from the bucket while dragging it backwards, or using a controlled 'slicing' motion.
• Using the side of the bucket to push large piles of material into the required depth.

Correct answer: Metering out smaller amounts of material from the bucket while dragging it backwards, or using a controlled 'slicing' motion.

Explanation: To achieve thin, consistent lifts for compaction, the operator should meter out smaller amounts of material. This can be done by slowly opening the bucket as it's dragged backwards or by using a controlled 'slicing' motion with the bucket edge. This technique ensures a manageable and uniform layer, which is essential for proper compaction. Dumping large loads or pushing piles would result in inconsistent depths.