Erosion Control March/April 2017 : Page 27

state dipped the fish out with nets and released them later [well away from the project site]. Then we had to refill the cofferdam.” This project was Durkin’s first time using the Dam-It Dams. He found them easy to install and notes that they have “a pretty good liner on the outside, a good protective cover. They hold the water back really well.” This section of the Niangua River has gravel on its bed. The Minnesota Limited crew saw some seepage with air pockets within the gravel, so they kept six pumps (6-inch size) running to take up the water that seeped through the gravel. Durkin says that in clay soil the Dam-It Dams would work very well. Other erosion control measures used at the project site included straw bales and wattles. Silt fence was moved fre-quently, as needed, and was sometimes right at the river’s edge. For most of the job, Minnesota Lim-ited operated with a crew of 30 workers. Other workers were added for specific parts of the work, increasing the crew size at one point to 80. Two islands, each measuring about 5 feet long and 25 to 30 feet wide, also had to be cut through for the pipeline installation. They added to the scenic nature of the farmland site. An access road was set up for the crew. It ran for 3 miles to the south side of the river. At the top of the hill the pipeline and a valve had to be placed under Cloverdale Road. “We had to cut 25 feet deep under the road, and it had to be closed to traf-fic,” recalls Durkin. The final portion of the work will involve restoring the land as it was before excavation began. Rye will be seeded first for quick cover, followed by grass and wildflowers, using a hydro-seeding machine. The pastures of the farm will be seeded with clover and timothy. Demolishing a Bridge A cofferdam was also required for a bridge project in Pennsylvania. This bridge demolition and replacement project was done by Deblin Inc. of Mechanicsburg, PA. The firm special-izes in public works projects involving bridges and other infrastructure. “PennDOT’s [Pennsylvania Depart-MARCH/APRIL 2017 ment of Transportation’s] District 8 is our home district, and we do quite a bit of work there,” says Tom Powell, Deblin’s vice president and the manager for this project. The bridge that carries State Route 743—known locally as Hershey Road—crosses over the Conewago Creek. It is situated between the cities of Conewago Township (in Dauphin County) and Mount Joy Township (in Lancaster County). Almost 14,000 vehicles travel across this bridge daily. The heavy traffic load and the years since its construc-tion in 1940 caused the deterioration that made PennDOT declare the bridge structurally deficient and approve its replacement. “The bridge was cast-in-place concrete, and it was in bad shape,” says Powell. Constructing the replacement bridge cost more than $3.1 million. Work was done in two phases so the bridge could still be used while construction was going on. “We set up temporary traffic signals at each end of the bridge,” says Powell. “Then we shifted traffic into the north-bound lane and demo’d the south-bound lane and part of the bridge.” The cofferdam was set up around the bridge’s pier and abutment number 1 for this work. In the next phase it was reset so that abutment number 2 could be removed and rebuilt. In the last phase, the cofferdam was flopped to the other side. Traffic was switched to the new southbound lane, and the old north-bound lane was removed and rebuilt. The project’s challenges were “an aggressive schedule, traffic that ran pretty heavily, and a tight work area. We had access to roads on the sides of the bridge. They opened them to us and we used them as staging areas,” says Powell. Conewago Creek’s normal depth is 6 to 7 feet. But during storms it becomes flashy because the land nearby has gentle slopes. PennDOT’s original specifications called for using sand bags and a concrete jersey bar. However, the creek’s flood depth made this idea impractical. The ground beneath the bridge had been scoured out by the Temporary Cofferdam Solutions for Erosion Control Projects Cost-effective -Proven free-standing design eliminates the need for costly sheet piling and heavy equipment. Versatile -Used in areas where other methods are not feasible. Schedule-friendly -Simple installation and removal can help keep your project on track, particularly when there are multiple phases. EROSION CONTROL 27

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