The Chicago Transit Authority has awarded a construction-management contract to Parsons Brinckerhoff for a rail replacement and tunnel rehabilitation project on the system’s Blue Line subway, which connects the downtown business district with O’Hare International Airport. The $88-million project is one of the first in Chicago to be fully funded by the American Recovery and Reinvestment Act of 2009. It involves replacement of 31,000 existing wooden half ties with new concrete half ties and 6,200 track feet of stone ballast with new concrete slab and direct fixation fasteners. The project also includes the installation of 29,000 ft of new rail
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.