Fifty-four floors high, the skyscraper that will house the new headquarters of Bank of America will is one of the largest excavation and foundation projects in New York. Already a focus of the media before construction began, the new building owes its fame to the many technological innovations that will serve to reduce the environmental impact and to state-of-the-art architectural details, such as the hanging garden created in the roof.
The geological characteristics of Manhattan have enabled one of the highest concentrations of skyscrapers per square mile in the world. The rock mass, while noted for its general hardness, is not distributed uniformly; depending on the area it has different consistencies making excavation a true challenge.
Manhattan bedrock, in fact, is made up of 170 different types of materials, with a prevalent make-up of metamorphic granite, gneiss, dolomite rock, schist and other formations noted for their hardness.The contractor assigned to the job, Civetta Cousins JV. of the Bronx, has been a name in the earthmoving business since the 1930s. Civetta took on the project using a hydraulic breaker to dig the pit (106 m in width, 259 m in length and 24 m in depth) that will contain the foundations and underground volumes.
According to John Lombardi, manager of Civetta Cousins JV, although breakers of other producers were present on the site, two Indeco 12000's had to be rented to increase productivity. Actually, the increase in productivity from the Indeco breakers allowed Civetta to get far enough ahead, that one breaker was replaced by a bucket to keep up with the material removal on the day of our visit.
With its 7.8 tonnes, an energy class of 16000 ft-lbs, and a rate of 240 to 550 blows per minute, the 12000, the largest breaker of the Indeco range, ensures exceptional productivity even when the application presents special challenges, such as the conditions on the Manhattan site. This was a consideration shared by John Lombardi:
"The Indeco 12000 immediately proved superior to the other equipment, and I'm not just referring to the size, but mostly to productivity. After hundreds of hours working away at the Manhattan bedrock I wouldn't hesitate to say the 12000 is ideal for a material such as this, which puts the excavators, equipment and operators to a hard test.
The breakers seem to completely ignore the hardness of the rock; it breaks it into much larger pieces than the other attachments working on the other side of the pit. We calculated that with the 12000 we could break over 45 cubic yards a day without effort, a level of productivity that may seem modest in absolute terms, but is exceptional when you're talking about Manhattan bedrock."