Stretching an entire city block, this 2.1 million sf, mixed-use development comprised of two residential towers (respectively 77-stories and 50-stories) connected by a ten-story podium and four levels of underground parking (820,000 gsf). It was constructed in a top-down method where the basement levels were simultaneously excavated as the towers rose above. By accelerating the vertical growth, our team reduced the schedule by eight months.
In total, the building features 735 rental apartments, 77 for-sale condominiums, 1,100 above and below ground parking spaces, 55,000 sf of offices, a restaurant, event space, a Whole Foods, a 125,000 sf Life Time Athletic Resort with an NCAA basketball court and four swimming pools, putting green, demonstration kitchen, multiple lounges, 120-foot-long elevated dog park, and a co-working space.
At the top of the taller tower are two liquid mass damper tanks which mitigate the effects of building sway for residents.
Constructing from the Top Down
A variety of traditional excavation sequencing, earth retention methods were explored when planning One Chicago. Given the sheer size of the jobsite, a full city block, the earth retention necessary to construct a four story basement was very critical. After exploring various internal and external earth retention bracing methods, it was concluded that a top down construction method would be the most cost effective and efficient method. Using the top down construction method, the below grade parking garage was retained by a 5' diameter secant wall and internally braced by reinforced concrete slabs. For the two residential towers, the concrete cores for each were constructed from the bottom-up within cofferdams (internally multi-level braced sheeting). The elevation of the internal bracing coincided with the parking slabs, which allowed for the earth retention at the cofferdams to be removed as construction progressed down each floor. A detailed sequence of events and safety plan was developed and implemented to manage personnel within the basement as well as manage exhaust and fresh air ventilation.
Constructing the basement at the same time as the two towers saved 6 months on the overall construction schedule and allowed for the below grade parking to open in advance of the residential units above.