Shafts are being formed for an East Side Combined Sewer Outflow (CSO) project in Portland, Oregon. The CSO is designed to significantly reduce sewage and storm water overflows into the city's Willamette River. These shafts are being created by constructing a slurry wall and then excavating within. Excavation is carried out using a Liebherr HS 895 HD duty-cycle crawler crane fitted with clamshell bucket. Periodically a drop chisel was required to loosen highly consolidated sand/silt/gravel formations.
Seven shafts, ranging from 49 ft to 67 ft in diameter and ranging from 120ft to 160ft deep, are being built along the route of the tunnel. Construction on these began in March 2006, paving the way for tunnel boring to begin in May 2007. As of mid-November 2008, six of the seven shafts had been completed.
On completion of excavation, the crane is also used to support the construction and installation of rebar mats, as well as tremie concrete operations, before moving on to the next shaft excavation operation.
The HS 895 HD is the largest model in Liebherr's series of duty cycle cranes. It has a maximum rated lifting capacity of 220 tons and has a maximum main boom length of 276 feet. Maximum boom length when fitted with clamshell or dragline is 181 feet. The 12-cylinder MAN diesel engine generates 900hp at 1,900rpm.
Clutch and braking functions on the free fall system are provided by a compact designed, low wear and maintenance-free multi-disc brake. The drag and hoist winches use pressure controlled, variable flow hydraulic motors, with sensors that automatically adjust oil flow to provide max winch speed depending on the load. The winch can produce a line pull of 66,200 lbs.
When completed in December 2011, the CSO will collect and intercept overflows from 12 existing combined sewer outfalls that discharge to the River.
Main contractor KBB, a joint venture led by Kiewit Construction with Bilfinger+Berger, is constructing a 22ft diameter tunnel, which runs for six miles along the east bank of the Willamette River in Portland and connects to a similar project on the west side at the Swan Island Pump Station. At $382.5 million, the East Side CSO - known locally as The Big Pipe - is the largest public works contract ever let by the City of Portland.
