Common Pile Driving Problems and Solutions
Pile driving is often a cost-effective and time-efficient support method. But because you're working with soil and other features in the earth, there is an element of the unknown, and things don't always go as planned. Not surprisingly, problems with pile driving usually are related to adverse soil conditions, which can lead to pile damage, hammer-pile alignment, and other issues. In most cases, stopping the work and testing the soil, reviewing or revisiting borings or calculations, and inspecting the equipment will help highlight the most likely cause of the problem.
Piles With Blow Count Above Minimum Pile Penetration Requirements
Confirm that 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 the driving system operation for conformance with the manufacturer’s guidelines.
If no obvious problems are found, take dynamic measurements to determine if the problem is related to the driving system or soil behavior. 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 (requires restrike to check), large soil quakes, or high soil damping.
Piles Driving Significantly Deeper Than Estimated
Soil resistance at the time of driving could be lower than anticipated, or the driving system performance may be 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 the drive system performance and restrike capacity with dynamic measurements.
- If the drive system performance is as assumed and restrike capacity is 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 the recommended change.
Abrupt Change or Decrease in Blow Counts for Bearing Piles
If borings do not indicate weathered profile above the bedrock/bearing layer, pile toe damage is likely. For piles that allow internal inspection, reflect light into the pile toe and tape the length inside the pile for indications of toe damage. For piles that cannot be internally inspected, take dynamic measurements to evaluate the problem, or consider pile extraction.
Blow Count Significantly Lower Than Expected
Review the soil borings. If they do not indicate soft layers, the pile may be damaged below grade. If the pile was spliced, re-evaluate the splice detail and field procedures for possible splice failure.
Lateral Movement of Previously Installed Piles When Driving New Piles
Pile movements are 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.
Piles Driving Out of Alignment
Piles may be moving out of alignment tolerance due to hammer-pile alignment control or 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.
Piles Driving Out of Location
Piles may be moving out of location tolerance due to hammer-pile alignment control or 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 or below the water table, or the soil is contaminated, excavation may not be feasible. Spudding or predrilling of pile locations may provide a solution.
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 on pile damage potential and soil matrix support characteristics. Additional piles may be necessary.
Concrete Piles Develop Partial Horizontal Cracks in Easy Driving
Check hammer-pile alignment because bending may be causing the problem. If the alignment appears to be normal, the tension and bending combined may be too high.
Concrete Pile Spalling or Slabbing Near Head
Determine pile head stress for observed blow count and compare with allowable stresses. If the calculated stress is high, add pile cushioning. If the calculated stress is low, investigate the pile quality, hammer performance, and hammer-pile alignment.
Concrete Piles Develop Complete Horizontal Cracks in Easy Driving
Determine the tension stresses along the pile for observed blow counts. If the calculated tension stresses are high, add cushioning or reduce the stroke. If the calculated tension stresses are low, check the hammer performance.
Concrete Piles Develop Complete Horizontal Cracks in Hard Driving
Determine the tension stresses along the pile. If the calculated tension stresses are high, consider a heavier ram. If the calculated tension stresses are low, take measurements and determine the quakes, which are probably higher than anticipated.
Concrete Piles Develop Partial Horizontal Cracks in Easy Driving
Check the hammer-pile alignment because bending may be the problem. If the alignment appears to be normal, tension and bending combined may be too high.
Steel Pile Head Deforms or Timber Pile Top Mushrooms
Check the following:
- Helmet size and/or shape
- Steel strength
- Evenness of the pile head
- Banding of the timber pile head
If all of these check out OK, determine the pile head stress. If the calculated stress is high, reduce the hammer energy (stroke) for low blow counts; for high blow counts, a different hammer or pile type may be required.
Unexpectedly Low Blow Counts During Pile Driving
If soil borings do not indicate soft layers, the pile may be damaged below grade. Investigate both tensile stresses along the pile and compressive stresses at the toe. If the calculated stresses are acceptable, investigate the possibility of obstructions or uneven toe contact on hard layer or other causes of pile toe damage.
Higher Blow Count than Expected
Review the wave equation analysis and check that all parameters were considered. Check the hammer and driving system. If no defects are found in the driving system, take field measurements. The problem could be preignition, preadmission, low hammer efficiency, soft cushion, large quakes, high damping, greater soil strengths, or temporarily increased soil resistance with later relaxation.
Lower Blow Count Than Expected
Soil resistance is likely lower than anticipated. Perform restrike testing. Establish the setup factor, and drive to lower capacity. Hammer performance may also be better than anticipated, so this should be checked.
Diesel Hammer Stroke Higher Than Calculated
If the field stroke is less than 90 percent of the calculated stroke, confirm that the ram friction is not a problem. Compare the calculated and observed blow counts. If the observed count is lower, the soil resistance is less than anticipated. If the blow counts are comparable, reanalyze with lower combustion pressure to match the observed hammer stroke.
Cannot Find Hammer in Data File
Look for a hammer of the same type and with a similar ram weight and energy rating and modify its data to fit the application.
No Hammer Within Driving Stress and Resistance Limits
Both the calculated stresses and blow counts are too high. Increase the pile impedance or material strength, or redesign for lower capacities. If the soil is fine-grained or known to exhibit setup gains after driving, the end-of-driving capacity may be selected lower than required. Confirm the capacity by restrike testing or static load testing.