Shoring Underground Parking Lot in Area With High Water Table – a Rarity in Region

There are few, if any, basements beneath the homes and office buildings of South Florida. The water table prevents most underground construction in the area, presenting a big challenge for contractors.

The Riviera Nursing Home and Rehabilitation Center in Coral Gables is a six-story state facility catering to those who require short- and long-term care as they transition from the hospital to their home. 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. Not only would the notoriously high water table jeopardize the garage’s construction, but the contractor would have to shore the soil to keep crews safe and ensure the stability of the buildings that rested above ground.

DooleyMack, general contractors focused on retail construction, contacted Sunbelt Rentals (formerly Mabey Inc.) Ft. Lauderdale office to develop a solution for this project. Our engineers developed a plan utilizing the contractors own 45-foot steel sheets and our Powerbrace framing system. The sheets, bolstered by the Powerbrace equipment, were driven into the ground to act as excavation walls and then encased in concrete to remain a permanent part of the foundation walls.

Sunbelt Rentals 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 a Sunbelt Rentals team member.

To combat this, DooleyMack hired divers to assist in the installation of the building’s concrete pilings and support systems before a 4-foot thick concrete slab was poured at the base of the excavation utilizing the tremie method. This stopped groundwater from penetrating the excavation and allowed work to continue.

Excavation was completed a short time later and the parking garage was completed in 2013. To date, it is the largest and deepest excavation on record in South Florida.