The Challenge:
Install cofferdams and place 60,000 cubic yards of concrete on the underwater level of the Holtwood Dam.
The Players:
Walsh Construction
ALL Erection and Crane Rental Corp.
The Process:
Three Potain tower cranes are helping expand a hydroelectric generation facility at the Holtwood Dam, located on the Susquehanna River near Holtwood, Penn., U.S.
The general contractor is Walsh Construction, which owns two cranes on the job - a Potain MR 615 and a Potain MR 415 - and is renting a Potain MD 485 B from ALL Erection and Crane Rental Corp. The cranes are configured with jibs that range in length from 131 to 145 feet, and will remain in this configuration throughout the job.
Nick Everson, a project manager at Walsh who oversees powerhouse construction, said the cranes are spaced to provide different lifting options.
“The construction site is approximately a 150-foot deep hole, 180 feet wide and almost 600 feet long,” he said. “We arranged the cranes so that any two cranes can reach almost all areas of the construction site at one time.”
The cranes are equipped with Potain’s Top Tracing anti-collision and controlled work zone software, which helps manage overlapping operation zones. The system also alerts the operator if the crane’s jib comes too close to another crane on the site. If the operator doesn’t react to this condition, a cut-off switch stops operation before impact can occur.
As an additional safety measure, Walsh configured the three cranes with the cabs all at the same level to allow eye contact between the operators. But because of the uneven terrain, each crane is a different overall height ranging from 146 to 221 feet high.
Walsh is working on the underwater section of the two-part powerhouse building. The company installed cofferdams on each side of the powerhouse and then used the cranes, fitted with concrete buckets, to place 60,000 cubic yards of concrete. Loads for this concrete work weigh 10 USt.
Throughout the project, the cranes will place concrete forms and reinforcing bars needed in the building process. The cranes will also help place some embedded components of the turbines. Sections of the draft tube liners for each of the turbines will be lifted into place using the cranes. These sections weigh approximately 15 to 17.5 USt.
The cranes will also help build the portion of the powerhouse that is at ground level and consists of structural steel and pre-cast concrete sections.
The three Potain cranes have been on the jobsite since October 2010 were scheduled to work through May 2012.
