SPECIALLANDMARKS :ISSUE FEATURE ARTICLE Digging Deeper: Top-Down Construction of the Marriott Marquis On May 1, 2014, the 6th Marriott Marquis in North America officially opened its doors for business according to schedule. This 4-Star, LEED Silver building boasts over 1.2 million sq ft (111,484 sq m) of usable building space, including nearly 1,200 guestrooms, over 75 meeting spaces and 6 food service outlets. The main challenge was fitting all of the amenities needed for the Marquis brand within the building space allotted: a two-acre site (8,094 sq m) and 130 ft (39.6 m) ceiling cap in the heart of downtown Washington D.C. To further challenge the project team, the building included a grand atrium, a one acre (4,047 sq m) skylight in the center of the tower, and a subterranean interface with the adjacent convention center, complete with loading docks and a pedestrian connector. The hotel also included a below-grade grand ballroom AUTHORS with 30,000 sq ft (2,787 sq m) of column- free space, and the incorporation of a live electrical duct bank that crossed the site. The solution: dig deep. In order to provide enough usable space for all of the hotel’s meeting rooms and support facilities, the excavation extended over 100 ft (30.5 m) below the street level, exposing soil that had not seen daylight since the Cretaceous period, over 100 million years ago. The only viable delivery method for a project of this magnitude and configur- ation was the approach of top-down construction. Top-down delivery allowed crews to construct the deep subgrade structure concurrently with installation of the building’s superstructure. The use of slurry walls, drilled shafts and diaphragm slabs were essential in overcoming the many challenges derived from the Marquis’ limited space. Slurry Walls The top-down construction began with a continuous slurry wall that was installed around the site perimeter. The wall was designed to act as the finished basement wall for the lower parking levels. A circular slurry wall shaft was also installed, which connected to the main slurry wall and formed the outer limits of the helical parking ramp to service the bottom two floors. The slurry walls ranged from 3 ft to 3.5 ft (.9 m to 1.1 m) in width and extended 120 ft (37 m) deep into a stiff, dense clayey sand to cut-off the recharge of water back into the excavation. In total, 95 slurry wall panels formed over 168,000 sq ft (15,608 sq m) of surface area and were filled with over 19,000 cu yd (14,527 cu m) of concrete and 1,800 tons (1,633 tonnes) of reinforcing steel. Three different types of end stops were used for the slurry wall: cast-in place, Nathan Rosenker and Andrew Cameron, Hensel Phelps Construction Company, and Giovanni Bonita, Ph.D., P.E., GEI Consultants, Inc. 58 • DEEP FOUNDATIONS • NOV/DEC 2014
