11. Concrete Piles Develop Complete Horizontal Cracks-Easy Driving.Determine tension stresses along the pile for observed blow counts. If high calculated tension stresses, add cushioning or reduce stroke. If low calculated tension stresses, check hammer performance.
12. Concrete Piles Develop Complete Horizontal Cracks-Hard Driving.Determine tension stresses along the pile. If high calculated tension stresses, consider heavier ram. If low calculated tension stresses, take measurements and determine quakes which are probably higher than anticipated.
13. Concrete Piles Develop Partial Horizontal Cracks in Easy DrivingCheck hammer-pile alignment since bending may be the problem. If alignment appears to be normal, tension and bending combined may be too high; solution will then be the same as for complete cracks above.
14. Steel Pile Head Deforms Timber Pile Top Mushrooms.
Photo by Fernandez Tadeo
Check helmet size/shape; check steel strength; check evenness of the pile head, banding of timber pile head. If okay, determine pile head stress. If calculated stress is high, reduce hammer energy (stroke) for low blow counts; for high blow counts, different hammer or pile type may be required.
15. Unexpectedly Low Blow Counts During Pile Priving.If soil borings do not indicate soft layers, pile may be damaged below grade. Investigate both tensile stresses along the pile and compressive stresses at toe. If calculated stresses are acceptable, investigate the possibility of obstructions/uneven toe contact on hard layer or other reasons for pile toe damage.
16. Higher Blow Count than Expected.Review the wave equation analysis and check that all parameters were considered. Check hammer and driving system. If no defects are found in driving system, field measurements should be taken. 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.
17. Lower Blow Count than Expected.
By Fernandez Tadeo
Probably, soil resistance is lower than anticipated. Perform restrike testing. Establish setup factor and drive to lower capacity. Hammer performance may also be better than anticipated, check.
18. Diesel Hammer Stroke Higher than Calculated.The field stroke is less than 90% of the calculated stroke. Check that ram friction is not a problem. Compare calculated and observed blow count. If observed one is lower, soil resistance is less than anticipated. If blow counts are comparable, reanalyze with lower combustion pressure to match observed hammer stroke.
19. Cannot Find Hammer in Data File.See if there is a hammer of same type, similar ram weight and energy rating and modify its data.
20. Cannot Find A Hammer Within Driving Stress and Resistance LimitsBoth calculated stresses and blow counts are too high. Increase pile impedance or material strength or redesign for lower capacities. If soil is fine grained or known to exhibit setup gains after driving, then end of driving capacity may be chosen lower than required. Capacity should be confirmed by restrike testing or static load testing.