A top-down construction plan, created by J. F. White Contracting Co. Inc. on the Harvard campus, required versatile equipment that can work in tight spaces, but the overall benefits of the plan include a shorter, more efficient building cycle. Work on the $50-million underground parking garage started by pouring perimeter slurry walls some 70 feet deep, creating a 320 by 180-foot footprint. Next, support columns were installed at specified intervals after which the contractor poured a concrete roof surface with three 20 by 15-foot glory holes. One level at a time, excavation was completed and a concrete floor was poured. To accomplish that, excavating equipment had to be able to work under a 10-foot ceiling - an impossible task for conventional knuckle boom excavators.
"We lowered six Model XL 2200 Gradall® excavators through the glory holes and lined them up to move dirt from one to another," said Jim Cahill, project manager. "One Gradall dug the 'face' of the soil and passed the material back to the others to load out of the glory hole using a crane with a clam shell attachment." The Gradalls worked 12 hours a day. "Because of their low profile and telescoping boom design, the Model XL 2200 excavators were the only machines we could use to work efficiently under 10-foot ceilings," said Cahill. "Plus, they were able to scrape the inside walls clean because they could turn their buckets." By building from the top down, Cahill said his company saved a month or more on this 26-month project because crews could start working earlier on higher floors while lower floors were still being excavated. That included early installation of electrical/mechanical equipment, which is based on the top floor. Once completed, plans call for a science lab to be built over a portion of the garage. Another section will be covered with dirt, creating a green space and a playground.
For more information about Gradall excavators call (800) 445-4752.