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.