The Rowan is a new six-story residential structure in the Astoria neighborhood of Queens, New York. The developer boasted that “we are creating a product that hasn’t existed in Astoria—a modern, thoughtfully designed condominium building that has all the high-end finishes and amenities you see across the city.” An unusual and interesting aspect of the development is the 35-foot deep excavation for several cellar levels for an automated parking system, a novel use of underground space which hadn’t been done before in Astoria.
GZA worked with the project team to develop geotechnical recommendations and support of excavation design. Excavation support and underpinning up to 35 feet with multiple levels of lateral supports were required to provide control over the movement of abutting buildings, utility, infrastructure, and roadways.
The support of excavation system includes soldier piles with timber lagging, underpinning piers and multiple levels of lateral support. Compared to other options, tieback anchors allow more working space within the excavation and were selected.
Soldier piles installed with a vibratory hammer were preferential from a commercial standpoint. By implementing an innovative observational-based approach, less expensive soldier pile installation techniques were allowed to be used to save construction expenses and durations.
Several rounds of design changes had to be made to accommodate the contractor’s logistical and commercial preferences, and GZA provided quick, timely turnaround and efficient communication with the design team that maintained the client’s timetable.
The cost effectiveness and performance of the excavation support and underpinning design were essential. By introducing innovative solutions, we helped to reduce our client’s construction expenses and duration, and the excavation was completed ahead of schedule.
A technical paper summarizing the project was published and presented at the 2019 ASCE Metropolitan Section Geo-Institute Chapter Annual Seminar and the project won a Gold Award in the 2020 ACEC New York Engineering Excellence Awards Competition. The project was also featured in the Winter 2019 edition of the design develop construct journal.