If it is necessary to advance the piling through a strong or stiff layer where refusal is possible, an additional pile penetration note as follows may be required, "The contractor’s attention is drawn to the hard material in the soil profile, jetting and/or pilot holes may be necessary to advance the piling to the required penetration depth.”

Be aware that under these conditions of potentially high driving stresses, a wave equation drivability analysis is necessary to ensure piles can be driven to required embedment depth. Higher grade steel can be specified if needed to meet drivability criteria. Coordinate any changes in the pile size, section, or tip elevations with the structural engineer. The geotechnical foundation engineer is responsible for reevaluating pile drivability during this iterative process.

Candidate pile types that cannot be driven to the required nominal resistance and/or minimum pile penetration without exceeding material stress limits and within a reasonable blow count of 30 to 120 blows per foot with appropriately sized driving systems should be eliminated from consideration. 120 blows per foot or 10 blows per inch is often considered refusal driving conditions by many hammer manufacturers.