Swimming to Jacksonville Underground

Sometimes, before you can start building a highway, you first have to build up the ground beneath it. That's what is happening in Florida's Citrus County as the latest phase of the Suncoast Parkway extension rolls on.

Ground-improvement specialists Menard USA are relying on ALL Crane Rental of Florida, a member of the ALL Family of Companies, to provide a series of cranes needed for ground-densification operations.

Superior Construction as the general contractor for Florida's Turnpike Enterprise, the project owner.

Citrus County, like many parts of Florida, is notorious for the presence of sinkholes. The state's limestone geology is an aggravating factor, as groundwater can erode the limestone and create holes and tunnels within the limestone layer. "This is especially true in areas where there is no layer of clay separating limestone from sand," said Robert Dubay, the south region safety manager for Menard USA. "The limestone is like Swiss cheese. The sand eventually shifts and filters into the holes and tunnels, creating vaults in the ground above that turn into sinkholes."

Dubay notes that Florida's limestone layer is so porous, there's an old saying that if a person could hold his or her breath long enough, they could swim from Key West to Jacksonville (a distance of approximately 500 mi.) completely underground.

Dubay's team is using three main types of densification processes for this phase of the Suncoast Parkway expansion: compaction grouting, the addition of wick drains and vibro sand compaction. It is this third process that requires the use of cranes.

Smaller crawler cranes from ALL are outfitted with a 20-in. vibrating probe followed by a 60-ft.-long tube that is 12 in. in diameter. The probe vibrates laterally as it bores into the earth. After reaching the limestone layer at a depth prescribed by an engineer (approximately 50 ft. below the surface) the cranes begin backing out the tubes. While this reversal is occurring, Menard USA's crew starts pouring new sand into the vertical tunnel left behind.

"This hardens the ground and ‘tightens' the hole," said Dubay. Cranes work the site in a grid pattern to ensure complete coverage.

So far, Menard USA has used three 80-ton Link-Belt 138HSL crawlers configured with 120-ft. booms. A fourth will be implemented soon. The probes and follow tubes are connected to the crane booms using 5-ft.-long, 1.25-in. diameter eye-to-eye chokers. The aim of all densification efforts is to prepare the ground to accept the weight of the coming highway as well as the traffic it will carry.

"Often when we're discussing road and bridge work, we're talking about cranes with long reaches and large capacities in excess of 500 tons or more," said Dennis Davis, sales representative of ALL Crane Rental of Florida. "This project serves as a reminder that our smaller equipment are critical assets, and that they're an important part of any well-rounded crane fleet."

Dubay said another collaboration between Menard USA and ALL is coming soon, as three more cranes will work to shore-up the ground for the Polk Parkway project, inland from the current job in Citrus County.

For more information, visit allcrane.com.