Lake Manatee Dam Rehabilitation Project Completed Near Tampa, Florida

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Hayward Baker has completed remediation work on Lake Manatee Dam. The nearly 50 year old dam serves as a freshwater reservoir for 300,000 residents in Tampa, Florida.

Hayward Baker Inc. (HBI), North America’s leader in geotechnical construction, recently completed remediation work on the Lake Manatee Dam located in Manatee County south of Tampa, Florida. The nearly 50-year-old dam, constructed of sandy soils with a clay core, serves as a freshwater reservoir for 300,000 area residents.

Significant erosion observed during annual inspections and supplemental subsurface investigations revealed a compromised dam core with areas of permeable soils, allowing excessive seepage through and under the dam, which threatened major flooding and depletion of the water supply if left untreated.

Priority remediation goals implemented included reestablishing seepage control via a new cutoff wall within the existing dam embankment and beneath the service spillway.

Remediation Scope

The scope of the remediation work ultimately consisted of a 3,300 feet long, nominal 2 foot thick cutoff wall to maximum depths of 105 feet below the current crest elevation. The cutoff wall required a minimum of 5 feet embedment into a deep underlying low permeable clay layer. The design required that the wall have a very low permeability of 1x10-6 cm/sec.

Emergency priority Phase I goals of remediation included reestablishing seepage control within the dam embankment and beneath the service spillway. To achieve this, HBI worked closely with the client, Manatee County, and its consulting engineer, AMEC, to develop a plan to achieve the goal.

As the focal point, HBI designed and constructed a Trench cutting Remixing Deep (TRD) cutoff wall located on the north and south sides of the spillway. The 105-foot-long chainsaw-like TRD vertical cutter was inserted vertically in segments by the crawler machine until the design depth of the wall was reached. The base crawler rig then moved along the planned wall alignment as the cutter post cut and mixed the soil with a cement binder constructing the wall in place.

The TRD wall tied into a jet grouted cutoff wall that HBI constructed beneath the spillway. The jet grout process advanced drill steel to the maximum treatment depth and then high velocity jets of cement slurry located at the tip of the drill steel mixed with the soil to create soil-cement columns as the drill steel was retracted.

The columns were constructed side-by-side along the planned wall alignment to create the cutoff wall. Most of the TRD and jet grouting were designed to be completed through the shell of the dam along the lakeside edge of the crest.

Quality control measures included a pre-production 40-foot long TRD cutoff wall test section, on-rig computer data acquisition of all construction parameters during both TRD and jet grouting operations, plus post-construction permeability testing.

“We found Hayward Baker to be a quality partner in this endeavor,” said Mark Simpson, Manatee County Water Division Manager. “We had a relatively short time to correct some major weaknesses in a critical piece of infrastructure, and HBI was able to overcome some substantial issues to get the job completed. The 3,300-foot-long cutoff wall was designed and completed within 10 months, all while we maintained operation of the reservoir and uninterrupted service to our customers,” he added.

Curtis Cook, Vice President of HBI stated, “The depth, performance requirements and constraints of the project made this a perfect candidate for our TRD and Jet Grouting techniques. As a specialty contractor, it is professionally fulfilling to have the full range of tools to help clients solve difficult geotechnical issues – and an added pleasure to be able to work with the professional team of Manatee County and AMEC. Once again, our crews made us proud by successfully constructing a high quality product while under the pressures of a tight schedule.”

For more information about the Lake Manatee Dam project in Tampa, as well as the ground improvement capabilities and services provided by HBI, contact Curtis Cook at (813) 884-3441 or CRCook@haywardbaker.com.

About Hayward Baker Inc.

Hayward Baker Inc. [http://www.haywardbaker.com is North America’s leader in geotechnical construction, annually ranked by Engineering News-Record (ENR) magazine as #1 in the profession. With a 60-year record of experience, Hayward Baker Inc. offers geotechnical construction technologies through a network of more than 20 company-owned offices and equipment yards across the continent. Project applications include foundation support, settlement control, site improvement, slope stabilization, underpinning, excavation shoring, earth retention, seismic/liquefaction mitigation, ground water control, and environmental remediation.

Hayward Baker Inc. is part of the Keller Group of companies, a multinational organization providing geotechnical construction services throughout the world. Web site address: http://www.keller.co.uk.

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