A Testy Situation
The Owner’s engineer had designed 48-inch diameter pipe piles 190-feet long to support the heavily-loaded industrial wharf. The design capacity is 1,900 kips each, so, the engineer specified dynamic tests to 3,800 kips to prove that the piles were sure to have achieved the necessary bearing resistance. It turns out that a dynamic test of that capacity requires more strength and stiffness than the pile walls could provide.
A Pile of Problems
The test hammer would bounce like a pogo stick on the pile head, or it would crumple the pile top like a beer can crushed against John Belushi’s forehead. The soils around the very long pile were simply stronger than the pile element itself, which made it impossible to test the soil strength by striking the pile.
This is called an “impedance problem” and it’s relatively uncommon. It only happens on very high capacity piles where the engineer tries to save money on materials by specifying very thin walled pipe. The Owner’s engineer, despite following standard design procedures, inadvertently required tests that defied physical law.
Uncommon Engineering to the Rescue
Weeks needed us to explain the impossibility in ways that made sense to both the Engineer and Owner and then, while maintaining a productive relationship, get the testing requirement stricken from the specifications and replaced with physically possible quality assurance program.
We wrote up a plan, supported it with case histories and technical references, and presented the replacement program to an all-hands project meeting. Proper planning and preparation, combined with good communication skills, carried the day. The program was changed, the dynamic tests could use the production hammer, and the project was back on track.