Project Update on Eastside CSO Tunnel!
Construction of the Eastside CSO Tunnel Project in Portland Oregon continues with an expected completion in the fall of 2011. The 29,000-foot long, 22-foot inside diameter tunnel, ranging in depth from 100 to 160 feet, will convey captured flows from Southeast Portland under the East Side Industrial Area to a CSO pump station on Swan Island. The tunnel alignment will intercept a series of gravity conduits and drop structures that connect to 13 existing combined sewer outfalls. Nine microtunnel drives—of 84-inch inside diameter reinforced concrete pipe, totaling 7,800 linear feet—will divert flows from the existing outfalls to the main tunnel. When this project is complete, the volume of combined sewage and stormwater that now overflows to the Willamette River when it rains will be reduced by more than 94%.
In November 2009, the north 20,500 linear foot (lf) portion of the tunnel excavation was completed. The tunnel boring machine (TBM) was then removed from the shaft, loaded onto a barge, and transported up the Willamette River. it was then lowered back into the driving shaft, this time heading south. And in March 2010, excavation began on the 8,500 lf south portion of the tunnel. As of July 2010, 3,400 lf of tunnel excavation remained.
Build-out on all seven of the large-diameter shafts is in various stages of completion. Inside diameters range from 49-feet to 67-feet, and are 112 to 153-feet deep. These large shafts were constructed either to facilitate the tunnel drive, or to contain one or two drop shafts for getting outfalls and interceptor sewer flows down into the tunnel.
In May of 2009, the last of the nine microtunnel drives was completed. The outfalls are either diverted directly into one of the large shafts or into a microtunnel that will convey the flow over to the shaft. Diversion structures that will divert flow from the outfalls to the tunnel are being constructed with the use of temporary flow pipes and bulkheads. Once the tunnel is completed, the temporary pipes and bulkheads will be removed, diverting the flows to the tunnel.
