Head Spall and Out-of-Plumb Leads
During driving of a 50-ft, 14-in square precast concrete pile, the hammer has made about 20 blows when the head begins to spall on one corner. The leads are visibly out of plumb-about 1.5°-and the pile is being driven off center in the lead. The diesel hammer is still operating, and the pile has advanced only 6 ft into a dense sand layer. The crew wants to keep driving because the pile is 'almost plumb' and the hammer is developing good energy. The pile cushion looks compressed and uneven, and the hammer guides show wear. The signalperson reports that the pile head is moving sideways with each blow. The job specification requires the pile to be driven within 1/4 in per ft of plumb and the pile head to be protected. You must decide whether to continue, stop, or reposition.
1. What is your immediate decision, and why?
Read the worked answer
Stop driving. The pile head spall and the sideways movement show the hammer energy is not going down the pile axis. The leads are about 1.5 degrees out of plumb; over 50 ft that is roughly 15.7 in of offset, which exceeds a 1/4 in per ft tolerance (12.5 in over 50 ft). The compressed, uneven cushion and worn hammer guides can worsen the eccentric loading. Continuing risks a cracked or rejected pile, damaged hammer guides, and a pile that kicks out of the leads. Lower the hammer, secure the leads, and keep the crew clear before inspecting.
2. What corrective actions and inspections are required before restarting?
Read the worked answer
Lower the hammer and support it; do not keep driving to straighten the pile. Inspect the pile head and cut back damaged concrete only with engineer approval. Replace the cushion with the specified material and thickness. Realign the leads using two levels or a plumb line at 90 degrees, check the hammer guides and anvil for wear, and confirm the pile is centered in the lead. Recheck the pile plumb in two directions before restarting, then drive at controlled energy and monitor the head and lead alignment. If the pile cannot be brought within tolerance, stop and get engineering direction rather than forcing it.
3. How should plumb be verified and documented?
Read the worked answer
Verify plumb in two directions at 90 degrees using a spirit level, plumb line, or survey instrument-not by eye from one side. Measure the pile offset relative to the specified tolerance over the driven length and record the readings before and after corrections. Check the leads and pile separately; a plumb pile in out-of-plumb leads still drives eccentrically. Record the cushion condition, hammer guide inspection, and any cut-off or repair. If the as-driven plumb exceeds the specification, do not cover or accept it without the engineer's evaluation.