Open for Business

July 9, 2008

About the author: Dave Handy is project manager for Griffin Dewatering South Florida, LLC. Handy can be reached at 954.969.8854 or by e-mail at [email protected].

When the Palm Beach, Fla., area was growing into the north end of the county, it became apparent that a new shopping venue was required. Residents would not want to travel all the way to the Island of Palm Beach to shop at upscale department stores.

Pepper-Southern General Contractors of Atlanta was hired by owner Forbes-Cohen Florida Properties in 1988 to construct “The Gardens Mall” in Palm Beach Gardens, Fla. Griffin Dewatering provided the proper methods and materials to be utilized when dewatering the proposed structures’ footings. The proposed footings were designed to support both floor slabs and structural columns as well as the new glass-enclosed central elevator and adjacent water features.

This work was successfully concluded in 1999, and the mall opened with great success. Nineteen years later, some of the shine was gone; the tile grout was stained, the elevator was old and it was time to give the mall a facelift.

In 2007, Whiting-Turner General Contractors’ Ft. Lauderdale office hired Griffin Dewatering of South Florida to provide a workable dewatering plan to facilitate the demolition of the old and construction of the new while maintaining a low profile to accommodate everyday mall business. Griffin’s contract for services included dewatering of excavated areas where the new Grande Fountain, its control vault and the new elevator were to be constructed.

Project Challenges

The Gardens Mall project presented major challenges, most notably:

  • Providing an appropriate dewatering plan to facilitate excavation and placement of underground plumbing lines, concrete structures and fountain/pool shell;
  • Establishing an environmentally compatible dewatering process so as not to disturb the daily business of neighboring stores and eateries;
  • Overcoming the limited availability of a disposal location for dewatering effluent; and
  • Performing night work after hours.

Implemented Solutions

Workers installed a perimeter wellpoint/wick point system with 1/12-in.-by-15-ft, or approximately 7 ft below excavation bottoms, screened and wicked wellpoints at approximately 48-in. centers, horizontally. This procedure minimized and in some cases eliminated soil movement from adjacent existing footings and slabs by reducing hydrostatic groundwater pressure to a point well below the excavated areas.

The dewatering pump is electrically powered and was placed in an enclosed box, thus keeping noise well below any audible level in the work area. A typical wellpoint pump’s vacuum system is mineral oil-lubricated and sealed, thereby emitting hydrocarbon vapor during the cooling and sealing process, which was a problem. To resolve this issue, Griffin South Florida contacted Griffin Southwest and Griffin Pump & Equipment for an appropriately sized electrically powered wellpoint pump with a water-cooled and sealed vacuum pump.

A newly refurbished Griffin Model 4NCRE with a Travaini vacuum pump was available and suited this project perfectly. The size was right to be placed inside the mall and transported through service corridors and the motor size worked with the available three-phase power. The general contractor installed a flexible steel exhaust line to the adjacent ceiling fans to vent any water vapor or groundwater odor.

For disposal of dewatering effluent, a floor drain was available, but only in a 3-in. size. This constituted a problem because the anticipated dewatering effluent yield was on the order of 500 gal per minute.

Griffin subsequently cut and replaced tile, installing a 300-ft-by-6-in. discharge line under the existing floor slab via a service corridor and into an outside service area where a 2,500-gal weir-type settling tank aerated the groundwater prior to its disposal into the onsite drainage system.

The night work was the easiest problem to address. Shifts started at 9:30 p.m. and concluded at 6:00 a.m.

The discharge line is to remain in place for future use by the owner when draining or servicing the new water features. This work commenced for Griffin Dewatering in April 2007 and was completed by September 2007.

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About the Author

Dave Handy

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