April 2010 Vol. 65 No. 4
Features
Shoring, Dewatering In Flood Zone
There are few, if any, basements beneath the homes and office buildings of South Florida. The cellar (root or otherwise) is a rarity there and if you’re in search of an underground parking garage, you may spend a lifetime looking.
Why, in a part of the country so congested with development and desperate for space of any kind, ignore the subterranean strata? The answer, simply, is water. The water table that belies the city of Coral Gables is just inches below the surface in some spots. Water prevents most underground construction in this area and presented one of the biggest challenges that Sarasota, FL-based DooleyMack Constructors of South Florida has ever faced.
Last year, ground was broken on the New Riviera Nursing Home and Rehabilitation Center, a six-story state facility for the elderly located in the densely populated city of Coral Gables, just south of Miami, FL. The building will be constructed on a small parcel of land adjacent to a school, bank and office buildings and in the middle of the city. To accommodate the facility’s staff and visitors, a 175-foot long, 125-foot wide and 25-foot deep underground parking lot had to be constructed and double as the building’s foundation walls. This was the challenge facing DooleyMack, who was chosen to spearhead the project. Not only would the notoriously high water table jeopardize the garage’s construction, but the contractor would have to shore the soil to ensure the safety of their crews and the stability of the buildings that rested on the ground above.
DooleyMack Senior Project Manager Brian Shirley turned to sales representative Bob Gray of the Ft. Lauderdale offices of Mabey Bridge & Shore Inc., a Baltimore-based renter of sheet piling, frames and other shoring products, to develop a solution that would conquer their garage shoring and foundation challenge. Mabey engineers developed a system utilizing the contractors own 45-foot steel sheets and Mabey’s Powerbrace framing system. The sheets, bolstered by the Powerbrace equipment, would be driven into the ground to act as excavation walls and then encased in concrete to remain a permanent part of the foundation walls later on.
Water, water everywhere
“It was a unique challenge for us,” said Gray “The soils here are tough, and water begins to flood almost immediately after digging begins.” Mabey’s proprietary Titan struts and corner braces provided lateral stability during excavation and once the sheets and frames were in place, DooleyMack excavated and dewatered the pit in two, 175-foot by 62.50-foot phases. In spite of the normally water tight interlocking sheets and pumping equipment, water was intruding at a rate that exceeded dewatering in each of the excavation’s sections.
“It was amazing; several feet of water would be pumped out each day but tidal changes would cause more water to flood in overnight. It was definitely an uphill battle,” explained Gray. To combat this, Dooley Mack hired divers to assist in the installation of the building’s concrete pilings and support systems before a 4-foot thick concrete seal slab was poured at the base of the excavation utilizing the tremie method. This stopped ground water from penetrating the excavation and allowed work to continue. When the first half of the excavation concluded over the summer, DooleyMack moved on to the second phase of the pit and again, Mabey’s framing and struts were used in tandem with the contractor’s sheets. The excavation phase of the project wrapped-up in early December before Mabey’s modular frames and equipment were removed. To date, it is the largest and deepest excavation on record in South Florida.
FOR MORE INFORMATION:
Mabey Bridge & Shore Inc., (800) 956-2239, www.mabey.com
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