Grading and Excavation Contractor

By Gini McKain

The massive population growth in South Florida during the past century has significantly altered the Everglades environment. Wetlands were drained to create dry land for farms and homes, reducing the size of the Everglades by half and polluting the remainder. Canals, roads, levees, and pumping stations were built to provide flood control. Vast farmlands added tons upon tons of pesticides and insecticides to the runoff water with major undesirable results. Today, in a more enlightened time, a total of over $11 billion is being invested to reverse this.

The massive undertaking by the South Florida Water Management District (SFWMD) 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. Nothing of this size, scope, and intensity has previously been attempted.

The existing SFWMD’s Stormwater Treatment Area #2 (STA-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 (ppb) and through natural filtration flow through the cells in STA-2, reducing this 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, as a result, to improve even further the water quality in the Everglades Protection Area.

This "heavyweight" provides a high-quality compactive effort at a fast pace.

This Cell is known as a submerged vegetation cell that contains a Naiad grass, which grows below the water’s surface, as opposed to an emergent vegetative cell that contains plants similar to cattails. 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. Then they turn north for about another 5,000 feet where they tie into another supply canal levee.

The “seeds” for the creation of the SFWMD were planted in the late 1940s by flood and drought. Today, the agency’s responsibilities include regional flood control, water-supply and water-quality protection, and restoration of the ecosystem. The district operates and maintains approximately 1,800 miles of canals, roads, and levees; 25 major pumping stations; and 200 larger and 2,000 smaller water control structures. With the current environmental needs, the district instituted a new program to accelerate the ecological remediation. Several private-sector contractors are being contracted to help with this. Rather than doing their own in-house engineering and geotechnical investigations as had been done in the past, the SFWMD subcontracted this out to Brown and Caldwell Engineering.

The Gulf Group and Bergeron Land Development Inc. are just two of the contractors involved in this endeavor. According to Project Manager Don Stetter, due to some SFWMD operational changes, the contract, now called Acceler8, is being prosecuted on a Fast Track basis. Bergeron is the earthwork subcontractor to the Gulf Group, the general contractor on the $18 million contract for the South Florida Water Management District’s Cell 4 expansion of Stormwater Treatment Area 2. The job involves handling a total of 1.2 million cubic yards of various materials for construction of water retention levees, roads, and berms.

The project will expand the size and enhance the performance of the existing stormwater treatment areas created as part of the Everglades Construction Project. These constructed wetlands naturally reduce stormwater runoff (phosphorus) pollution levels flowing in from the Everglades Agricultural Area primarily. Stormwater from roads and developments are another lesser concern.

Because of the extremely tight working deadline and the complexity of the soils and rock being handled, Bergeron recently imported a new high-tech Bomag BW225D-3 compactor. With its patented Variocontrol (BVC) system and its ability to easily achieve thick lift compaction densities, the machine was able to help solve the time-critical project problem.

With an operating weight at approximately 58,000 pounds, the Bomag is more than double the weight of many of the competitive compactors sold in the United States. The maximum centrifugal force converts to over 90,000 pounds. The bottom line for this “heavyweight” earthwork behemoth is that it provides a higher-quality compactive effort faster and at a lower cost.

“With all the levees averaging between 9 and 10 feet tall, that equates to making only three lifts instead of five. I feel that one of the best features about the new Bomag BW225D-3 is the fact that the compactor lets me know that it has done as much as it can for me. Anything else is simply a waste of time, energy, fuel, and money,” concludes Operator Diana Stetter. Construction Manager Ed Bashman of Brown and Caldwell, who represents the SFWMD, says that Bergeron Land Development requested permission to put down the rocky levee building material in 36-inch-thick lifts instead of the previously specified lesser amounts.

“We took a look at the request and agreed to do some studies, including some in-place testing. Bergeron had brought in a new Bomag compaction machine, which exerts a tremendous compaction effort. In order to prove this, we decided to actually go in and pothole down and test the density of the bottom 12 inches of the 36-inch lift. This was on the theory that if that lift met the specifications, the odds were favorable that the other two lifts above it would also meet the specs.

“At the same time we were also looking for the possibility of ‘rock nesting.’ This is where rocks cluster together and possibly form a flow path through the material, which is an unacceptable condition. So far, the geotechnical results have been very good. We have noticed no signs of nesting, and the density reading using Troxler nuclear testing equipment has met the specifications. Provided these results continue, we plan on using the same testing procedures throughout the remainder of this project.

“This is important because we have a time-critical 300-day completion deadline. The project is due to be flow capable by the end of this year, and there are stipulated $6,000-a-day liquated damages. That’s moving 1,200,000 cubic yards of tough lime rock. The material must be excavated, moved, put in place, and compacted, not to mention building the many water control structures associated with it.

Clearing ground level vegetation and mulch from underlying limestone

“I won’t say that anything the contractor requests of us we will do, but, if it sounds reasonable and makes good sense from a construction technology viewpoint, 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.

“The BW225D-3 actually has the ability to measure the compactive effort and can chart (on a hard-copy graph) progressively how the soil tightens up and measure this off its 84-inch drum as it vibrates. 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 you should make more passes or take density tests,” he adds.

Bomag’s Variocontrol single-drum rollers, as being used by Bergeron, incorporate an intelligent and powerful exciter system, which enables the contractor to adopt an efficient and effective onsite 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, according to factory specifications, indicates when further compaction is not possible. It consists of two accelerometers, the distance meter, and an electronic and a display unit for “on the go” compaction control. The BTM05 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 produces an Omega value. This denotes soil stiffness and can be correlated with the results of conventional compaction density tests. Depending on the type of material to be compacted, Omega values between 0 and 1,000 can be displayed. In general, Omega value produced on specific soils or granular materials will be higher where compaction is better.

“The rock being excavated and compacted out here is really tough. You can see that by the sharp edges from where it breaks when blasted. It’s almost like flint in some places. This is a rough place to work; there is nothing easy out here. The teeth on the excavator buckets are wicked; in fact, they call one of them the ‘Ugly Bucket.’ It is designed specifically to rip rock and, at times, it even has a hard time,” Stetter continues. “Because of its rock content there are so many variables in testing for density. One of these is simply getting a good, solid, flat testing surface. Another factor is that, if you are reading down on a rock and it is beside the source point and the Troxler receiver, you are likely to get a higher reading than normal. On the other hand, if it is on the other side of the source, you might get more reflection off the rock and your count could go higher and your density figure could go lower. To cope with this possibility we rotate the instrument 90 degrees and repeat the test. If the combination satisfies us, then the test is valid.”

The geotechnical testing engineers at NODARSE International elected to perform their Troxler nuclear density tests on the first (or bottom) 12-inch segment of the 3-foot-thick course of material. To do this they had Bergeron excavate a 2-foot-deep cut in the compacted fill. This was cleaned off to where a technician could set the machine on a level pad that was typical of the compaction of the overall lift. A minimum of 95% compaction density was required at every level.

The cross sections of the project, according to plans produced by the consulting engineers, Brown and Caldwell, indicate the typical levee to have a 14-foot width, a 3:1 sideslope, and a design elevation of 19 feet in height overall. The top of the levees are planned wide enough to be used as roadways with occasional safe passing zones. The majority of the inflow and spreader canals have a 34-foot wide bottom, 2:1 sideslopes, and an average of between 12- and 15-foot depth.

The first process in building both the new levees and canals is to clear that area of the saturated ground level vegetation and muck from the underlying limestone. This is usually dried and stockpiled for later reuse. A large tracked dozer is used for this.

The limerock is then drilled and blasted on a 15- by 16-foot square pattern. 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 and stockpiled when not put on the levee location.

The BW225D-3 compactor is just one of many such high-technology “tools” being employed to carry out that mission. In another instance Don Stetter points out an 8-cubic-yard hydraulic excavator that is outfitted with only a 4-cubic-yard rock ripping bucket to give it more power to rip out the limerock substrate.

Damco drill rigs were drilling 4.75-inch-diameter holes 10 to 13 feet deep, on a 15- by 16-foot square pattern. On a normal 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.

There were no overt indications that Bergeron Land Development’s bright yellow vibratory compactor was probably in the process of forever changing the history of roadbuilding in America. As its operator, Diana Stetter, made the typical 80-inch-wide passes, it was not apparent that the machine was successfully compacting a 36-inch-thick lift of rocky limestone fill with minimum effort. That was all taking place below the line of sight.

Gini McKain is a photojournalist specializing in construction activities.

GEC - November/December 2006

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