Read the investigation with its limits

Start with the boring logs, recovered material and site history. Record the depth and location of coarse particles, rubble or rock. Use the classification system stated in the logs for cobbles and boulders, and retain measured dimensions or photographs where available. A borehole samples one location; an isolated object can lie between investigation points.

Read SPT refusal with the recorded blow count and penetration under the specified procedure. A high count or incomplete penetration can reflect a coarse particle or sampler obstruction as well as strong ground. CPT resistance peaks or refusal also need correlation with samples and adjacent investigation. Neither test alone identifies a boulder, proves rockhead or establishes pile capacity.

The geotechnical team may use trial pits, probing, additional drilling or geophysics to reduce uncertainty. Select each method for the target depth, ground and access. Correlate geophysical interpretation with direct investigation. Complete utility checks before intrusive investigation.

References: 1, 2

Respond to an unexpected change in driving

Before production, the engineer should define the driving criteria, pile stress limits and stop conditions. Specify who records the event, who can stop work and who approves the response. The operator should follow that procedure if penetration falls, blow counts rise, the pile loses alignment or damage is suspected.

Record the depth, penetration or blows, hammer settings and observations. Check pile alignment, head condition and the clamp or impact interface. Compare the event depth with the ground profile and nearby piles. For impact work, review hammer performance and driveability before increasing energy. Further driving can worsen damage if the toe has struck an obstruction.

Keep investigation refusal separate from pile-driving refusal. Also distinguish an unexpected stop from the project’s specified termination criteria. The responsible engineer must assess pile condition, minimum penetration and the required capacity evidence before accepting the installation.

References: 2, 3

Approve the method change before continuing

The project team may consider removing a known obstruction, predrilling, changing the pile toe detail or revising the foundation arrangement. A pile shoe can protect or strengthen an approved toe detail, but it does not guarantee passage through a boulder. Guide frames and leads help control alignment; they do not remove an obstruction.

Predrilling can reduce driving resistance and change shaft or toe resistance. The engineer must assess the effect on capacity and acceptance, and specify the hole diameter, depth and treatment. Check bore support, groundwater and spoil handling where drilling requires them. Do not extend the drilled zone beyond the approved limits without review.

Jetting also changes the ground around the pile. Use it only where the project permits it and after the engineer has checked its effect on the foundation and nearby ground. If removal or installation aids cannot provide an acceptable solution, the designer may need to revise the pile location, pile type or foundation method.

References: 2, 3

Match equipment to the approved sequence

Vibratory driving may suit compatible piles in favorable granular overburden. A vibratory hammer is not a rock-drilling tool. A stalled pile needs review of the ground, pile and operating conditions before the team changes equipment. Do not assume that a larger vibratory hammer will pass a boulder or buried concrete.

An impact hammer may suit an approved driving or seating stage. Check the hammer-pile system using the driveability analysis and project criteria, including expected blow counts and pile stresses. Review the helmet or drive cap, cushions where required, alignment and energy settings. Impact energy alone does not confirm that the pile can pass an obstruction without damage.

BRUCE can review SGV vibratory and SGH hydraulic impact equipment for the selected sequence. That review needs the pile drawing, ground investigation and approved method. Check the equipment interface, hydraulic supply and crane capacity at the working radius. The project’s responsible designers and site team retain design, lifting, monitoring and acceptance duties.

References: 2, 3

Keep the encounter and acceptance records

Record the obstruction evidence, pile position and event depth with the action the engineer approved. Keep removal or drilling records, revised driving settings and pile condition checks. Compare the installed pile with the specified depth, alignment and acceptance requirements.

Use restrike, dynamic measurements or static load tests where the project specifies them. A penetration rate or blow count alone cannot establish capacity. If damage is suspected, the responsible engineer must assess it and define any inspection, testing, replacement or remedial work before acceptance.

References: 2, 3