When performing geotechnical work in an urban environment, every plot of land is uniquely challenging and requires quick and careful thinking. One of our projects in the center of Queens, adding an automated parking system to a six-story residential project to the Rowan condominium project, underscored this. The client had strict budget requirements; the buildings next to the excavation had to remain in use by residents and businesses; a neighboring property would also be doing excavation work; and we were on the clock, breaking ground in April 2017 for work that had to be complete before the winter of 2018.
Then, of course, there are the challenges that arrive when you start the project. Initially our design called for single phase, full 20ft depth piers, but a quick redesign was required to stay on schedule when the Contractor encountered cobbles and boulders in the initial piers and to accommodate their preferences. We shifted the design to multi-phase underpinning, which brought a fresh challenge.
In this situation, soldier piles set with a vibratory hammer were the clear choice; they would be faster to install and better fit the client’s budget, compared to drilled piles, which require individual manpower and more time to install. However, using the hammer raised the question of settlement and vibration, particularly as we would be working below the foundations of buildings around us. We had to be certain there would be no impact on the surrounding properties.
We designed and implemented a demonstration program using vibration measurements at certain distances to test potential impact on surrounding buildings. With that data, we were able to determine we could use the hammer. However, we paired that technique with careful inspection and real-time vibration monitoring to ensure both efficacy and safety, ready to shift if conditions demanded it.
Our responsive redesign approach to the underpinning, other field conditions discovered during construction, and multiple design team and client requests kept the job on pace. Despite a second pier excavation, multiple redesigns, and tight deadlines, paired with the client’s ongoing reminders of the risk to the project delays would cause, we provided efficient turnaround for the client that maintained the timetable.
Ultimately, we beat the clock, finishing in December 2018. We helped reduce construction expenses, kept the time needed to install support and underpinning to the client’s schedule, and did so with innovative solutions and geotechnical know-how. As a crowning touch, the project won a Gold Award from the American Civil Engineering Council’s New York chapter in 2020 in the Structural Systems category.