Green Dredging, Green Pumping
Green Dredging, Green PumpingInnovative Combination of Equipment and Materials Implement Unique Environmental Dredging Technologies
STURTEVANT, WI (February 2, 2010) – Highly ingenious environmental construction techniques, utilized in the first construction phase of the Illinois River Basin Restoration Program, have likely set the stage for handling future shallow water and soft sediment dredging projects in both a green-friendly and highly efficient manner.
A Putzmeister BSA 14000 HP-D 11-inch (280mm) trailer-mounted concrete pump, in an unusual application of pumping sediment from a lake’s bottom instead of its typical use in placing concrete, strategically teamed up with a Cable Arm® clamshell bucket and crane; a specially-engineered screening device; and MacTube™ geotextile containers, which resemble enormous sand bags the size of four semi-trailers paired side by side. This rare combination of equipment and materials implemented innovative and environmentally-friendly dredging technologies believed to be the first ever employed in a soft sediment application.
Going to Great Depths
The clever approach entails dredging sediment, filtering it and then reusing the dredged material by pumping it into the geotextile containers that will form the perimeter of an artificial island – offering a beneficial way to reuse dredged sediment and an inventive way of applying a concrete pump’s technological features to a new application. This special method is being applied during construction of the Peoria Riverfront Development, Illinois Upper Mid-sized Island Critical Restoration Project under the Illinois River Basin Restoration Authority – Section 519 of the Water Resources Development Act of 2000 (WRDA 2000). The efforts of Section 519 WRDA 2000 relate to restoring and enhancing the 30,000 square-mile (77,700km²) Illinois River Basin’s ecosystem.
As the largest bottomland lake in the valley, Peoria Lake, like many other lakes, has experienced the loss of ecological integrity due to sedimentation, especially noted in deeper off-channel parts of the lake going from a maximum eight foot (2.44m) to a minimum one foot (0.30m) depth in recent years. Consequently, the loss of aquatic and wildlife habitat is viewed as the greatest threat, followed by diminishing aesthetic values and recreational opportunities.
The U.S. Army Corps of Engineers, Rock Island District, and the Illinois Department of Natural Resources, with input from other agencies, identified opportunities and meticulously engineered and designed a unique restoration plan to improve depth diversity and enhance aquatic habitat, with ancillary recreational benefits.
Green Light to Proceed
As the first of 16 critical restoration projects, the contract for Stage I of the two-stage Peoria Riverfront Development project was awarded on March 19, 2009 to Midwest Foundation Corporation (Midwest) of Tremont, Illinois for $2,723,500. It involves constructing a perimeter for creation of a 21 acre (8.5 ha) island, which will be accomplished by dredging more than 15 acres (6ha) for a channel around the island's perimeter and using geotextile containers for its structural border.
“Establishing an island in the middle of this lake is tough to accomplish with its shallow water, soft clay sediment and its mud consistency,” says Troy Hythecker, civil engineer for the U.S. Army Corps of Engineers.
Midwest was up for the challenge. For the past 35 of its 40 years in business, the general contractor has focused on major bridge construction, demolition and rehabilitation; docks and terminals; as well as lock and dam rehabilitations throughout the Midwestern United States and Texas.
Mechanical Dredging Specified
For the special task, Midwest employed a high solids mechanical dredging process, as the more common hydraulic dredging method was specifically excluded as an option in the project’s specs.
“We needed a way to put the lake’s soft sediment into the geotextile containers without adding water. Using a hydraulic dredging process, which adds water, would result in dredged material with existing fine grain sediment that would clog the pores of the containers required to form the island,” says Randall Kinney, civil engineer with the U.S. Army Corps of Engineers. “It’s also difficult to get environmental permits because of turbidity and habitat issues.”
“Hydraulic dredging is basically pumping muddy water since 95 percent of it is liquid,” notes Tim Troyer, Midwest president. “On the other hand, the mechanical dredging approach we’re using maintains a high solid content with only 40 percent liquid. Therefore, we’re pumping less water and more solids for less turbidity and more efficiency.”
Unique Fleet Results
To accommodate marine work, Midwest’s fleet encompasses a variety of cranes, excavators, pile hammers, barges and tug boats. However, to execute this challenging project, the company recently welcomed unique equipment additions – the world’s largest trailer-mounted concrete pump, a patented clamshell bucket and a one-of-a-kind screening device.
This equipment will join a 100-ton crane and various other machinery and tools on a barge that will remain on water for the duration of the project. However, to even reach the work site required dredging an access channel 545 feet (166.12m) long, 110 feet (33.53m) wide and five feet (1.52m) below existing ground, starting from the main navigation channel.
Once this step was accomplished, the project’s main task began. It required dredging a channel five and a half feet (1.68m) lower than existing ground at a 5,754 foot (1753.82m) length and 80 foot (24.38m) width. It will create a kidney-shaped island surrounded by containers positioned three in a row to form its mile-long (1.6km) perimeter.
Ingenious Dredging Process
In basic terms, the construction process involves a crane operating a clamshell bucket, which lifts sediment and deposits it into a screening device designed to filter out debris and transfer the remaining sediment to a trailer pump’s hopper. The trailer pump then pumps the material through eight-inch (200mm) diameter delivery line, extending distances up to 1,000 feet (304.8m) while floating on water with the help of marking buoys.
A pontoon excavator also assists in moving and connecting the delivery line to a container’s fill port. Once the sediment reaches the fill ports atop a container, it is deposited inside, filling one container at a time.
By involving the trailer pump in the process, the dredged sediment is quickly, easily and cost-effectively transferred from point A to point B, which eliminates one of the most time-consuming and highest expense in dredging – transportation and disposal costs.
“To our knowledge, this is the first time anything like this has been attempted, because it is certainly not common to our industry,” says Doug Bryan, estimator/project manager at Midwest. “To handle this high profile project with the greatest efficiency and least environmental disruption, we applied several different construction techniques and combined various types of equipment.”
Trailer Pump in Unfamiliar Waters
The resourceful use of a trailer-mounted concrete pump to pump the sediment is an example of Midwest thinking outside the box. Before purchasing the pump, the general contractor carefully compared brands to find the model best suited to meet the job’s demanding needs.
“We did a lot of research and selected Putzmeister’s BSA 14000 HP-D trailer pump with larger 11-inch (280mm) material cylinders and longer 83-inch (2,100mm) stroke to handle this specialized application,” says Troyer. “Watching the unit in action confirms we made the right choice.”
Although the concrete trailer pump finds itself in unfamiliar waters, pumping an out-of-the-ordinary material in an extraordinary application, the rugged machine still came equipped with all standard features, no modifications. Beyond the standard large-sized material cylinders, this includes the unit’s RS 900M “Big Mouth” hopper with high 21.2 cubic foot (600L) capacity; robust nine- to seven-inch (230 to 180mm) S-Valve to quickly gulp down the sediment; and exclusive free flow hydraulic system for smoother, more controllable pumping, while additionally achieving low fuel consumption.
To keep up with the fast-paced dredging process, the trailer pump’s maximum 1,146-psi (79 bar) pressure and up to 260 cubic yard (200m³/hr) output provides both high pressure and high volume on the rod side. Its 630 hp (470kW) diesel-powered Caterpillar® engine provides plenty of power in pumping the dredged material long distances at high outputs.
“Putzmeister’s positive displacement trailer pump with its high output was the only way for us to achieve our production goals and meet the project’s specifications,” says Troyer. “The pump is certainly doing its job, as it’s getting the material to the containers without any issues.”
Recognizing the trailer pump’s instrumental role on this project also highlights its versatility in applications beyond pumping concrete, Kinney says, “It’s much easier to set up delivery line for a quarter-mile (0.40km) and move material through it using a positive displacement trailer pump compared to the few other alternatives available that would have been cost-prohibitive.”
Clamshell Bucket Achieves Low Water Content
Also key to the process is Cable Arm’s navigational level-cut clamshell bucket, which offers a turbidity-free descent and ascent of the bucket and the ability to precisely remove material without leaving potholes in the lake’s bottom.
Operated by a crane, the bucket picks up mostly solids, not water, using open vents that allow water to flow through the bucket as it quickly descends into the water, and closed vents to keep material inside the bucket until it reaches the surface where excess water can then drain. In addition, the six cubic yard (4.59m³) capacity bucket with its 10 foot by 11 foot (3.05 x 3.35m) footprint digs more sediment in fewer cycles to achieve a speedy high solids dredging process.
“As we have never performed a project like this before and we don’t know of any like it, we have no comparisons in productivity,” says Dan Nelson, Midwest project manager. “However, we matched the crane and bucket’s capabilities with a pump that could also achieve a 260 cubic yard an hour (200m³/hr) output; and as a result, when pumping, maximum production is available.”
"Although the pump and bucket perform flawlessly to get the maximum output," says Troyer, "we do face logistical challenges such as locating the containers, moving delivery line and other factors that prevent this type of high output eight hours a day."
Special Screening Device
Unable to source a device for screening out debris before the dredged material is dumped into the trailer pump’s hopper, Midwest engineered a special invention that was fabricated locally. The innovation resembles an enormous hopper with a 16 cubic yard (12.23m³) capacity and rugged grizzly grate that filters out unwanted debris.
The all-steel construction apparatus sets above the trailer pump’s hopper while stabilized by four reinforced leg braces. Its sloped sides funnel the debris-free sediment into an outlet, which covers the outside perimeter of the trailer pump’s hopper while cushioned with a rubber seal.
“We couldn’t take a chance of not screening the dredged material,” says Nelson. “It keeps out debris such as branches that could plug up the pump’s delivery line, which would be time-consuming and difficult to unclog, especially on the water.”
Containers Create Island Perimeter
To create the island’s structural perimeter, MacTube™ geotextile containers met the stringent specifications of the contract. The containers’ soft armored structure, constructed of high-strength geotextile fabric woven in a rip-resistant weave pattern, offers minimal impact to the environment; and when filled to a 420-ton (380-metric ton) capacity with the dredged sediment, the giant containers are 100 feet (30.48m) long, six feet (1.83m) high and 45 feet (13.72m) in circumference.
“The geotextile containers are typically filled with sand; and to my knowledge, they have never been successfully filled with soft sediment while employing hydraulic dredging,” says Kinney. However, all of that changed with this project’s high solids approach; and as a result, the containers are being filled without difficulty.
“We’re pleased with how well the overall project is progressing,” says Jack McDaniel, area engineer for the U.S. Army Corps of Engineers. “Midwest is doing a good job, the equipment is working well, and we’re even exceeding various specifications, such as achieving a higher percentage of solids than the 50 percent specified.”
In large part, credit for this achievement can be given to the clamshell bucket’s ability to dig a high solids material and the trailer pump’s ability to pump it without mixing the material and water into a blended consistency. Therefore any excess liquid coming out the delivery line, although very minimal in this application, can theoretically drain through the fines pores of the container's fabric and return to the waterways. Furthermore, additives or polymers are not needed to aid in the dewatering process for this sediment-based application, which further realizes substantial cost savings and avoids contaminants.
Completion on the Horizon
Dredging began in July 2009, and completion of the island’s perimeter is slated for November 2009. As part of Stage I, Midwest must next construct a 200-foot-long (60.96m) test section where another container will be stacked on top of the lower three containers and a berm built behind it. Completion of this step is slated for early 2010.
Once the entire first stage is finished, 125,000 cubic yards (95,569m³) of sediment will create the island perimeter of 165 geotextile containers, test section and interior berm.
Green Future Ahead
The key components – trailer pump, clamshell bucket, screening device and geotextile containers – proved to be the ideal combination to effectively accommodate the job’s specs. However, during the process, Midwest employed other time- and labor-saving techniques of a proprietary nature to further improve efficiency and ensure conservational benefits.
“Undertaking this unique construction project has better prepared us for handling even greater challenges on similar projects ahead,” concludes Troyer. “This is especially important because we see environmental construction technology as the way of the future.”