Dewatering Key To SR-414 Bridge Success

By Steve Hudson | September 28, 2010

In Florida's Orlando-Orange County, particularly in areas such as Apopka and northwest Orange County, roadway capacity is sometimes stretched to the limit — and beyond — as existing highways struggle to handle ever-increasing traffic counts.

To help alleviate the congestion, and to accommodate expected future growth, the Orlando-Orange County Expressway Authority is extending State Road 414 (Maitland Boulevard) westward for nine miles from U.S. 441 to SR 429, then northwest to U.S. 441 near County Road 437. The resulting highway — a six-lane elevated toll road — is being built in phases with multiple contracts in each phase.

Phase 1, now under construction, involves new construction from Maitland Boulevard at U.S. 441 to just west of CR 435, plus construction of a short connector road to allow access to SR 429. Multiple contractors are involved in this phase of the effort, which should be completed in 2009.

Working on the east end of the project is Hubbard Construction Co. Hubbard's $89-million contract involves construction of approximately 1.5 miles of new roadway — and as Hubbard superintendent Bob McKee puts it, the project is "almost all bridge."

Hubbard's McKee explains that plans for this portion of the work call for construction of 20 bents, each with multiple (typically four) footings which vary in size. These footings are constructed on piles — concrete piles up to 100 feet long in some areas, and longer steel pile in others. Deepest penetration to refusal has been about 106 feet. Typically, cuts of about 19 feet have been required.

It's an ambitious project with lots of footing construction. But the area's high water table means that extensive dewatering must be done before any footing construction can be completed.

To dry things out and allow excavation and footing construction to move ahead, Hubbard Construction called on Holland Pump to provide a Holland W12R pump for some serious dewatering. The pump is connected to a 600-foot wellpoint system to dewatereach work area and allow construction to move ahead.

A "Very Wet Project"

"It is a very wet project," notes Greg Chevalier, Holland Pump's Orlando branch manager, and Hubbard's McKeenotes that the dewatering operation has to "stay in front of the guys pouring the footers."

"Dewatering an individual work area takes several days," McKee says, adding that dewatering must be completed before any excavation for the footers can begin.

Needless to say, proper operation of the dewatering system has been extremely important to keeping this phase of the project on schedule.

"The wellpoint pump must run about three days before we can begin excavation," McKee says, "and then the pump has to continue to run until the footer and column are formed and poured."

As water is pumped from the ground during wellpointing, it is filtered through the screens of the wellpoints and then pumped into a small holding area near the construction zone. From there, it is transferred through an 8-inch pipe passing under an active rail line to a second and much larger holding area about a mile from the project site. Passing beneath the rail line required a 45-foot-long bore.

Pump Operation Critical

Wellpoint pump operation is critical not only throughout the dewatering operation but also during subsequent excavation and concrete placement. Without the pumping operation, the excavation would quickly fill with water — something that becomes especially critical during concrete placement.

To make sure the pump is in optimum operating order, careful attention is given to maintenance. Additionally, like other Holland pumps, the W12R used on the project features Holland's HANS system, which provides pump operating parameters via cell phone. The HANS system would also alert key parties, including Holland pump maintenance specialists, if for any reason the pump quit operating.

McKee notes that the project's pumps are monitored 24 hours a day to make sure that all are working as they should.

"We have someone out here constantly checking the pumps," he says. "If one of the pumps were to quit, then we would have a lot of cleanup to do."