Jan. 16, 2012 04:27

Reconstruction of a Pond

Erosion is a problem that affects states, communities and residential areas alike.

Mother Nature’s natural wear and tear is brought about by a variety of events—from the violence of storms to the gentle flow of a river—or by man-made intrusions.

Dealing with these issues has lead developers to devise a means to help combat this inevitable wearing away of the land. There are many products available on the market today, but here we’ll focus on one product that can be considered a permanent solution to the violence of hurricanes or other storms, as well as providing a solid foundation for riverbanks and roadways.

A reclamation pond located in Sarasota, Florida, recently underwent an overhaul designed to provide a permanent, solid foundation to prevent the breakdown of the pond’s wave breaks.

Hi Hat Ranch Pond A is a manmade pond built about 25 years ago as a storage facility for the city’s reclaimed effluent water, treated in the city wastewater treatment plant. The pond came about following a Florida law enacted in 1973, restricting communities from pumping treated wastewater into area bays. At that time, the city of Sarasota was pumping treated wastewater into the Sarasota Bay.

According to Sarasota Public Works Manager Dale Haas, once the law was enacted, Sarasota officials began to explore the options available to the city. Haas said officials looked at a local ranch that raised cattle, tended orange groves and other various produce. At the time, the ranch was using the same groundwater for irrigation as the city was using for the residents. City officials determined that the situation could benefit both the ranch and the city. The city of Sarasota proposed to purchase a small section of Hi Hat Ranch land and construct a reclamation pond, where treated wastewater could be stored and later used for irrigation of the ranch grazing land, orange groves and sod fields. A contract was drawn up and signed.

Haas said that the city installed irrigation piping to various fields, as well as to the 110-acre pond. Advanced treated water flows through the pipes daily and is used for irrigation. Any remaining water not used immediately on any given day is stored in the pond for later use by the ranch. Florida’s winter months are dry, Haas noted.

The city of Sarasota finished building the pond in 1987. The original design consisted of earthen wave breaks around the perimeter of the pond, leaving the pond vulnerable to the wear and tear of the weather. The pond did well, Haas said, until 2004, when a series of hurricanes hit the area, causing substantial damage to the pond.

“Those storms came with such frequency and force that the waves broke down the earthen wave breaks,” Haas said. More storms in 2005 compounded the problem, leaving the city with serious dam age to the pond. Since the damage was due to hurricanes, Haas added, the city was able to get disaster funding from FEMA for the rebuild.

The next step was to come up with a plan for the reconstruction of the pond. “We had two choices,” Haas said.

The city could rebuild the pond with the original specifications, or they could consider a permanent concrete liner that would withstand Florida’s hurricanes year after year. Haas said the city chose the more expensive but permanent solution. “The engineers determined the concrete liner was a better use of the money,” he concluded.

The city brought in local engineering firm AECOM to handle the design and help with the permitting and preparation of the bid documents. AECOM also provided construction phase services. As the $3 million project got underway, engineers consulted with R.H. Moore & Associates, a distributor of cable concrete block, to determine the size, weight and construction of the block.

Design engineers considered various block configurations, ultimately narrowing the decision down to two choices. Those choices included an 8.5" thick wet-cast product manufactured onsite or a prefabricated interlocking block measuring 4.5" thick. The smaller block was to be made in a plant and transported to the site. Haas said the city looked at the pros and cons of the two manufacturing processes, including quality of product and transportation costs. General Contractor QGS Development chose the thicker wet-cast product manufactured onsite.

“The thicker block was chosen to combat the wave action created during a severe storm event,” said Jeff Peterson, a representative for R.H. Moore & Associates.

The bid was ultimately awarded to International Erosion Control Systems, out of Tampa, Florida. IECS, a company with 25 years experience in the development and manufacturing of erosion control products, makes many different products that can be used in a variety of situations. Manufacturing product onsite is a specialty of IECS. “The ability to manufacture product onsite can save a customer substantial cost in the end,” said IECS President Charles Chase.

RJ Services LLC, a subcontractor that provides manufacturing labor to IECS, set up on location to pour the mats. The product included an 8.5" thick open cell 55 concrete block cabled together in 8' x 16' and 8' x 14'8" sizes. Over the years, IECS has developed mats in a variety of sizes and weights, depending on the specifications of a specific project. The mats are poured in 8' x16' steel forms resembling an ice cube tray. There are 72 individual cells per form. When pouring an open cell mat, a cone is bolted to the center of each cell, leaving a round opening in the middle of each poured cell. The opening allows vegetation to grow.

Erosion control mats can also be poured as solid blocks, and in a variety of thicknesses. The mats are poured with either stainlesssteel cable or a strong rope called poly-steel cable. The cable is laced in both directions on the form, providing the tendons by which the individual blocks are held together. This makes the mat pliable, allowing it to lie smoothly over uneven ground. The specifications for the Hi Hat Ranch Pond rehabilitation required stainless-steel cable.

The geotextile materials are made with polypropylene fibers and come in a variety of weights . . . the different weights are designed to add different levels of drainage and strength to a project. It helps to keep the soil in place while allowing water to flow through the system, providing separation of water and soil.

The cable is looped in short single lengths across the length of the form for each row of cells. Another single length of cable is cut long and fed back and forth across the width of the form. The long strand of cable is held in place by hooks attached to a single long bar running the length of the form.

The bar is turned and locked into place with steel pins. The cable sits in V-shaped crevices that are cut into each cell wall, bringing one cable underneath the other as it is poured and raked level to the top of the form. The forms are sprayed with a form-release product.

The mats are typically poured using concrete batched at a 4,000pound mix. Once the concrete is raked level to the top of the form, a worker follows behind with a concrete vibrator, working each cell to help the concrete settle smoothly into the form. After the mats are poured, they are left to cure overnight.

The following morning, the forms are flipped over with a large forklift loader equipped with a boom. An I-beam bar is secured to the forks of the loader, and flipping chains are attached with steel clevises to the ends of the bar. A thick, flat rectangular piece of steel is attached to the changes with eyelet holes cut in the center. The flipping chains are placed on spindles that extend from each end of the form.

As the loader lifts the form, it flips over. The forms strike the ground on each side, causing the mat to loosen from the form. When it is lowered, workers will strike the frame of the forms with sledge hammers to further loosen the mat. Each mat will eventually drop out of the center of the form, bowing as it remains held fast by the long bars on each side. The mat is then stacked and the bars are released, to fully drop the mat from the form. As the form is lifted off the mat, it flips back upright and is set in place, to be strung and poured again.

On the Sarasota job, the specifications required the mats to cure for a minimum of three days before they could be laid around the perimeter of the pond. QGS job manager Jimmy Byrd said the job required 254,000 square feet of block to be installed around the perimeter of the pond. “We arrived on the job and we cleared and grubbed the vegetation and the slope,” Byrd said.

Byrd said QGS imported 19,000 yards of fill for the job. The fill was used to create a three-to-one slope. The job then required QGS to dig a trench to provide embedment for the mats. A filter fabric was then laid providing a foundation for the mats. “The purpose of the geotextile material,” Byrd said, “was to hold the soil in place.”

The mats were laid around the slope in 8' x 22.67' sections. This was accomplished by laying two 8’ x 14'8" mats side-by-side, and laying one 8' x 16' mat horizontally on the bottom of the two shorter mats. Each set of mats covered two 8' x 22.67' sections.

This configuration was not how the mats were first ordered; they had been ordered as 8' x 21' mats. The original order required the mats to be poured in an 8' x 16' section and a shorter 8' x 5' section.

The two sections were to be clamped together and laid perpendicular to the base of the pond as one long mat. It became apparent that this would be time consuming, slowing down the overall project.

A meeting between engineers, the city of Sarasota and the contractors lead project organizers to determine that laying the mats in sets of three would cover the desired square footage while speeding up overall production, allowing the general contractor to meet a tight completion deadline.

Before the mats could be laid, workers rolled out the geotextile material provided by Willacoochee Industrial Fabrics, Inc., of Willacoochee, Georgia. WINfab manufactures a variety of woven and nonwoven fabrics that are used for foundation material in several different types of erosion control projects.

“These fabrics provide separation, filtration and reinforcement to the cabled concrete system,” said manufacturer’s representative Ken Bedenbaugh. The manufacturer’s website says the fabric “resists ultraviolet deterioration, rotting and biological degradation.”

The geotextile materials are made with polypropylene fibers and come in a variety of weights. Bendenbaugh said the different weights are designed to add different levels of drainage and strength to a project. It helps to keep the soil in place while allowing water to flow through the system, providing separation of water and soil. The condition of the soil, particle size and how hard or soft the ground is all play a role in determining the suitable product for a project, Bendenbaugh concluded.

WINfab 600N is the style of fabric chosen for the Hi Hat project. Bendenbaugh said this fabric is a mid-weight nonwoven geotextile material that “allows for acceptable drainage while providing a stable cushioned base for the mats.”

QGS Development laid the mats in place using a crane with a steel-lifting bar. The mats weigh between 6,500 to 7,200 pounds each. The lifting bar is equipped with two spreader bars, complete with six hooks on each side. The hooks are attached to the loops on each side of the mat. The crane swung the mat out over the slope and workers helped to guide it into place.

As the mats were laid in place, the workers clamped the mats together using stainless-steel clamps. The project called for a granular or rock fill to cover the mats from the waterline to the bottom of the pond, while topsoil was used to cover the mats on the upper section of the slope above the waterline. Byrd said QGS Development’s turf division finished the project by laying sod and hydroseeding local grasses on the exposed sections of the pond above the waterline.

Hi Hat Ranch Pond A is designed to hold approximately 180 million gallons of treated effluent or reclaimed water. With the completion of the project, Haas said the city does not expect to need to do a major rebuild of Hi Hat Ranch Pond A. General maintenance is expected to keep the pond in good working order indefinitely.

EDITOR’S NOTE: Rebecca Johns is International Erosion Control Systems Job Manager/RJ Services LLC

Also in Soil Erosion News

In many ways, we are fortunate that, in our chosen profession, we are able to help people when certain disasters occur: the tornadoes in Missouri, Oklahoma, Louisiana and Georgia, the flooding in Louisiana, the snows in the northeastern part of the country, the rain in California, and the snow in Colorado....

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