Common Pile Driving Problems and Possible Solutions to be Implemented.
1. Piles With Blow Count Above Minimum Pile Penetration Requirements.
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Check the pile has sufficient drivability and that the driving system is matched to the pile. If the pile and driving system are suitably matched, check driving system operation for compliance with manufacturer’s guidelines. If no obvious problems are found, dynamic measurements should be made to determine if the problem is driving system or soil behavior related. Driving system problems could include preignition, preadmission, low hammer efficiency, or soft cushion. Soil problems could include greater soil strength than anticipated, temporarily increased soil resistance with later relaxation (required restrike to check), large soil quakes, or high soil damping.
2. Piles Driving Significantly Deeper Than Estimated.
Soil resistance at the time of driving could be lower than anticipated or driving system performance is better than anticipated. Perform restrike tests after an appropriate waiting period to evaluate soil strength changes. If the ultimate capacity based on restrike blow count is still low, check drive system performance and restrike capacity with dynamic measurements. If drive system performance is as assumed and restrike capacity low, the soil conditions are weaker than anticipated. Foundation piles will probably need to be driven deeper than originally estimated or additional piles will be required to support the load. Contact the structural engineer/designer for recommended change.3. Abrupt Change or Decrease in Blow Counts for Bearing Piles.
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If borings do not indicate weathered profile above bedrock/bearing layer, then pile toe damage is likely. For piles that allow internal inspection, reflect light to the pile toe and tape the length inside the pile for indications of toe damage. For piles that cannot be internally inspected, dynamic measurements could be made to evaluate problem or pile extraction could be considered.
4. Blow Count Significantly Lower than Expected.
Review soil borings. If soil borings do not indicate soft layers, pile may be damaged below grade. If the pile was spliced, re-evaluate splice detail and field procedures for possible splice failure.5. Lateral Movement of Previously Installed Piles When Driving New Piles.
Pile movements likely due to soil displacement from adjacent pile driving. Possible solutions include redriving of installed piles, change in sequence of pile installation, or predrilling of pile locations to reduce ground movements. Lateral pile movements could also result from adjacent slope failure.6. Piles Driving Out of Alignment.
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Piles may be moving out of alignment tolerance due to hammer-pile alignment control or due to soil conditions. If due to poor hammer-pile alignment control, a pile gate, template or fixed lead system may improve the ability to maintain alignment tolerance. Soil conditions such as near surface obstructions or steeply sloping bedrock having minimal overburden material may prevent tolerance from being met.
7. Piles Driving Out of Location.
Piles may be moving out of location tolerance due to hammer-pile alignment control or due to soil conditions. If due to poor hammer-pile alignment control, a pile gate, template or fixed lead system may improve the ability to maintain location tolerance.
For piles encountering shallow obstructions:
If obstructions are within 3 feet of working grade, obstruction excavation and removal is probably feasible. If obstructions are at deeper depth, are below the water table, or the soil is contaminated, excavation may not be feasible. Spudding or predrilling of pile locations may provide a solution.
8. Pile Obstructions at Depth.
If deep obstructions are encountered contact the engineer for remedial design. Ultimate capacity of piles hitting obstructions should be reduced based upon pile damage potential and soil matrix support characteristics. Additional piles may be necessary.9. Concrete Piles Develop Partial Horizontal Cracks in Easy Driving.
Check hammer-pile alignment since bending may be causing the problem. If the alignment appears to be normal, tension and bending combined may be too high. The possible solution is as above with complete cracks.10. Concrete Pile Spalling or Slabbing Near Head.
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Determine pile head stress for observed blow count and compare with allowable stresses. If high calculated stress, add pile cushioning. If low calculated stress, investigate pile quality, hammer performance, hammer-pile alignment
