After about a month, the dam was removed and the Des Plaines River was able to flow unimpeded.
A Link-Belt 240 LX long-reach excavator was used to place toe stone along the river banks, while a Link-Belt 300 was paired with a Chicago Pneumatic RX25 hammer to break up the concrete dam.
The long-reach excavator and a tracked carrier helped place toe stong more quickly that anticipated and heavily contributed to the success of the project.
Machines were filled with Ecoterra hydraulic fluid to minimize damage if a leak occured, but there were no leaks.
The dam to be removed was adjacent to a historic tower which required careful consideration of the vibrations created when breaking the concrete.
The Chicago Pnuematic RX25 was fitted with an under water kit.
Accurately placing toe stone was one of the key challenges faced by Illinois Constructors Corp.
Dam removal presents a unique set of challenges, and the proper tools can make all the difference. So when the Army Corps of Engineers awarded Illinois Constructors Corp. the contract to remove the Hofmann Dam across the Des Plaines River near Riverside, IL, the company relied on specialized tools to complete the project.
Elburn, IL-based Illinois Constructors Corp. has established a reputation for the successful building of roadway, railway and marine projects. “We are a small- to mid-size general contractor,” reports Jim Carson, project manager.
The company traces its roots in the Chicago area back to the mid-1920s. The general contractor has the ability to self-perform work with its own skilled union workforce, and generally performs structural and site demolition, excavation and concrete forming and placement.
“Our company is predominately heavy civil construction — mainly bridges and structural work,” says Carson. The company also removes dams and rehabilitates shorelines.
The scope of the $3.1 million Hofmann Dam project went well beyond the dam removal. “The removal of the dam really wasn’t a large amount of work,” says Carson. “There were quite a lot of other things that had to happen.”
First, stone needed to be strategically placed along the river banks to prevent erosion. “We had to place about 9,000 tons of toe stone, which is basically a rounded cobblestone, upstream of the dam along the river banks to prevent the bank from eroding into the river,” says Carson.
This would be no easy feat. “We had to install 75% of the toe stone prior to removal of the dam,” Carson notes. Much of this material needed to go underwater, which meant equipment operators would be unable to see where it was being placed.
But before any stone could be laid, the equipment had to be able to access the site. “To start off, the main challenge was to establish a location where we could put a road into the river,” says Carson. The thickness of the required road also had to be calculated to support the weight of the equipment used to place the stone.
In addition, there was a downstream portion of the project in Riverside. “It was a low point that was protected by walls on both sides,” recalls Carson. One or two times each year, this area would flood the adjacent park. “It would not drain properly. The only way for the water to drain out would be for the water to evaporate. We re-graded that whole pond and installed a culvert, so when it does flood, it will drain out properly.”
Putting the Stones Into Place
Illinois Constructors owns an extensive fleet of equipment that includes excavators ranging from 15,000 to 125,000 lbs., as well as friction and hydraulic cranes. However, specialized equipment was required to most efficiently complete all phases of the dam removal project.
“This is a very unique project that requires a very specific scope of work,” says Carson. “If we think it is the best way to do it, we will obviously put the equipment in the bid to get the job done.”
Illinois Constructors rented an LBX Link-Belt 240 LX Long Front. This is a 58,900-lb. excavator with a 26-ft. 3-in. arm length and a 48-ft. digging depth. It can handle buckets ranging from .82 to .95 cu. yds. The long-front machine made it possible to effectively reach into the river and place the toe stone.
To get the stone from the staging area to the excavator, Illinois Constructors rented a Morooka MST-2200 rubber track dump carrier, which has a hydrostatic transmission and is able to navigate river terrain. “Basically, it was capable of handling 9,000 or 10,000 lbs. of stone,” says Carson. “We used that machine to track back and forth in the water between where the long-boom machine was placed and the rock.”
The company’s Link-Belt 300 loaded rock into the dump carrier from the stockpile. “The Morooka was moving the rock to the job location where the long-boom machine would place it,” Carson explains. “That was basically the operation for about a month and a half — placing the toe stone in the river along the river embankments.”
Thanks to careful planning and the use of the rubber tracked dumper and long-reach excavator, Illinois Constructors was able to move and place the stone much faster than anticipated. This saved both time and money.
“Those two machines really made this a successful project,” says Carson.
Getting the Dam Job Done
Once the stone was in place, the Army Corps of Engineers gave Illinois Constructors the green light to begin the dam removal. The company utilized its Link-Belt 300 with a 3,970-lb. Chicago Pneumatic RX25 hydraulic hammer designed for 20- to 33-ton carriers. Since the hammer would primarily be used under water, it was equipped with an underwater attachment kit, which uses an air compressor to force water out of the hammer to prevent damage.
The RX25 hammer, which incorporates advanced noise and vibration damping technology, was specifically chosen for the task because of a historic tower located adjacent to the dam. “We had requirements in our contract to monitor vibrations and ensure the Army Corps of Engineers that we would not damage that structure,” says Carson. “We couldn’t just use the largest hammer we could find to start breaking out the dam.” The hammer was sized to specifications provided by an engineer who performed a structural analysis.
As part of the demolition process, an access road to the dam was built so that broken concrete could be hauled away. The decision on where to place the haul road was critical.
“We were allowed to use some of the broken concrete from the dam to assist in our haul road,” says Carson. “But it was really a challenge to make sure we placed the haul road in a location where it was productive and we were able to remove the most amount of concrete per hour.”
Of course, working in a waterway presented special environmental concerns. Two measures were taken to mitigate any environmental impact. To avoid any sediment, a turbidity curtain was installed on the downstream side of where the rock material was being placed. And the company replaced all of the hydraulic fluids in its equipment with Conoco Ecoterra to minimize the potential consequences of a leak, which never occurred.
Ecoterra Hydraulic Oil is a zinc-free anti-wear oil specifically developed for use in industrial and mobile equipment operating in environmentally sensitive areas. It’s nontoxic to fish and aquatic species as determined by OECD Test Method 203 1-12, and is classified as inherently biodegradable by the OECD Test Method 301B. It also passes the visual “no sheen” requirements of the EPA Static Sheen Test.
This oil is much more expensive than traditional hydraulic fluid. “It actually costs a significant amount of money to get the oil that was in the Link-Belt 300 replaced with the Ecoterra,” Carson admits.
These efforts were rewarded by successful project completion with minimal environmental impact. Started in late 2011, all work on the project — including removal of two dams along the river and comprehensive improvements to a nearby park — was completed the following October. ET