State-of-the-Art Compaction Technology Helps Heal South FL Everglades

By Dan and Gini McKain | September 28, 2010

The massive population growth in South Florida during the past century has significantly altered the Everglades environment. Wetlands were drained to create dry land. Canals, roads, levees, and pumping stations were built to provide flood control. Vast farmlands added tons of pesticides to the runoff water with undesirable results.

Today, in a more enlightened time, more than $11 billion is being invested to reverse this.

The massive undertaking by the South Florida Water Management District is an effort to significantly improve the quality of water in the Everglades Protection Area. It is the largest project of its type in the world.

The existing SFWMD's Stormwater Treatment Area #2 is a 6,430-acre constructed wetland treatment system located in southern Palm Beach County. Presently it is divided into three cells which operate in parallel. The original design of STA-2 was for receiving agricultural runoff waters containing an estimated total phosphate concentration of 50 parts per billion and, through natural filtration flow through the cells in STA-2, reducing phosphorus to no more than 20 ppb. The primary objective of the ongoing STA 2/Cell 4 expansion project is to provide additional treatment capability and further improve water quality.

This cell is a submerged vegetation cell that contains a Naiad grass which grows below the water's surface. The levees are all approximately 14 feet wide at the top. The base level is about 73 feet across. The two levees under construction are about 12,500 feet long, and they turn north for about another 5,000 feet to tie into another supply canal levee.

The "seeds" for the creation of the SFWMD were planted in the late 1940's by flood and drought. Today, the agency's responsibilities include regional flood control, water supply and water quality protection as well as restoration of the ecosystem. With the current environmental needs, the district instituted a new program to accelerate the ecological remediation, and several private sector contractors are being contracted to help with this.

SFWMD subcontracted engineering and geotechnical investigations to Brown and Caldwell Engineering, and according to Project Manager Don Stetter the contract (now called Acceler8) is being completed on a fast track basis. Bergeron Land Development Inc. is the earthwork subcontractor to The Gulf Group, the general contractor on the $18-million Cell 4 expansion project. The job involves handling a total of 1.2 million cubic yards of various materials for construction of water retention levees, roads and berms.

Because of the extremely tight working deadline and the complexity of the soils and rock being handled, Bergeron recently imported a new Bomag BW225D-3 compactor outfitted with the Variocontrol (BVC) system to help achieve thick lift compaction densities. The machine has an operating weight of approximately 58,000 pounds, plus a maximum centrifugal force of more than 90,000 pounds.

The first step in building the new levees and canals is to clear that area of the saturated ground level vegetation and muck. This is usually dried and stockpiled for later reuse. A large tracked dozer handles the task. The underlying limerock is then drilled and blasted on a 15-foot by 16-foot square pattern. Damco drill rigs were drilling 4.75-inch diameter holes 10 feet to 13 feet deep, and on a typical day the two rigs were able to punch down an average of 100 to 150 holes before blasting was done. Orica Powernap powder was used for blasting. Fragmentation was good.

Large hydraulic excavators then either sidecast or stockpile the crushed material to drain and dry, or outload it into Terex TA30 end dump haulers. The levees are built from the adjacent canal material, which is stockpiled when not put on the levee location.

The new Bomag BW225D-3 has the ability to measure the compactive effort and can chart (on a hard copy graph) progressively how the soil tightens up. It gives the operator, by way of red or green go/no-go indicator lights, a very good indication of where any weak spots are and where more passes or density tests should be made.

The Bomag BW225D-3's Variocontrol single drum rollers, as being used by Bergeron, incorporate an intelligent exciter system, which enables the contractor to adopt an efficient and effective on-site compaction management program. The new Terrameter BTM is a support system for owners, engineers and roller operators. It is used as an integrated working tool for continuous surface area assessment of compaction and load bearing capacity of granular soils, rock fills and unbound bearing courses. It provides a direct test for soil densities during the compaction process.

The Bomag Terrameter relies on the relationship between the acceleration of the vibrating drum and the dynamic stiffness of the soil to measure compaction output. The measuring system monitors the acceleration and indicates when optimum compaction has been achieved, saving time and money.

Construction manager Ed Bashman of Brown and Caldwell, which represents the SFWMD, said that Bergeron Land Development requested permission to put down the rocky levee building material in 36-inch thick lifts instead of the previously specified thinner lifts.

"We took a look at the request and agreed to do some studies including some in-place testing," Bashman said, adding, "We decided to actually go in and pothole down and test the density of the bottom 12 inches of the 36-inch lift."

At the same time, he added, the test was for the possibility of rock nesting, a situation where rocks cluster together and possibly form a flow path through the material — something which would be unacceptable.

"So far," he said, "the geotechnical results have been very good. We have noticed no signs of nesting, and the density readings using Troxler nuclear testing equipment have all met the specifications. Provided these results continue, we plan on using the same testing procedures throughout the remainder of this project."

If new approaches and the use of new equipment capabilities make good sense from a construction technology viewpoint, Stetter says, "We probably will agree to take a look at it. If it proves out and will speed the project along we will try to work with them to implement it. That's simply taking advantage of today's changing technology."