Once the bottom elevation of the foundation was established, Ryder-Wilcox returned to establish pins for each of the forty 40-foot piles required to support this two-building residence. As part of designing the foundation of this structure, surveyors and engineers dug observation holes to allow them to establish soil profiles to determine both pile depth and the mean high-water level (which provided the lowest possible elevation of foundation, or bottom of the slab). These two factors combined to determine the optimal height of the pile caps. These calculations aside, driving a pile is not a perfect science; in the case of the Cape Cod Hemp House, the piles are tapered to assist in driving, but ultimately there is always a chance they could shift a bit. These are friction piles meaning that they are driven to resistance, not bedrock.
Step two of driving the piles made work at the site even less popular. A diesel powered, air compressive, impact hammer was brought on site to drive each of the forty piles to resistance… Bam! Ping! Bam! Ping!
After pinning piles it should have been ‘ready, set, go,’ but this is where things started going sideways in the neighborhood. Though they are common in this area for marine structures, piles are almost never required for residential construction on the Cape and therefore do not usually impact residential areas. In the case of the Cape Cod Hemp House, which is not on a secluded lot, the neighbors were most certainly impacted. Chats with neighbors on the corner, as well as the Building Commissioner became part of the routine. But more on that in a moment.
Driving piles is a two-step process: a vibratory hammer drives them part way, followed by an impact driver to finish the job. The vibratory hammer used to set the pile and start the driving is less impactful to the ground overall. Essentially, it picks up the pile, sets it in place, and then uses rapid vibration to guide the pile down as the sand freely gives way. There is no real friction at this point, and you get into the ground water quickly which ‘sinks’ the pile with very little force for the first 15-20 feet. This started the neighborhood wondering what was going on and as you might assume in what is usually a sleepy beach town, the Building Commissioner immediately started getting calls. Luckily for the project team, a stop work order was never issued, but this did create the silver lining of forcing permits to be finalized (after waiting close to three months).
Together with the commissioner, the crew re-established protocols for driving the piles, including additional assurances from the structural and marine engineers on their inspections, daily visits from the commissioner’s office, and three seismic monitoring points at the north and west property lines. Perhaps to the chagrin of the neighbors, according to seismic reports, the activity levels were within acceptable range for the US Bureau of Mines and the work continued.
Step two of driving the piles made work at the site even less popular. A diesel powered, air compressive, impact hammer was brought on site to drive each of the forty piles to resistance… Bam! Ping! Bam! Ping! as the hammer dropped and was hoisted back up with each blow, radiating the seismic (but allowable!) forces until each pile moved no more than 1” per 10 strikes. By the end of August, the hammers were finally silent, just in time to wrap up summer vacation.
