Final Breakthrough for NSP Stage 2
Friday, February 26, 2010, marked the completion of tunnel excavation for Northern Sewerage Project’s (NSP) Stage 2 with the breakthrough of the NIS Section 1 drive, a 1.2-kilometer (3,940-foot) section between Newlands Road and the Carr Street shafts. The first 500 meters (1,640 feet) of this drive were excavated using drill-and-blast methods because of the prevailing ground conditions, which consisted of good-quality basalt. The remaining 700 meters (2,300 feet) were excavated by “Victoria,” a 3-meter-diameter (10-foot) Herrenknecht earth pressure balance (EPB) tunnel boring machine (TBM). Challenges faced and successfully overcome by Victoria included a shallow crossing of Merri Creek and passing within 3 meters (10 feet) of the existing Merri Creek Reliever sewer tunnel.
With shaft and tunnel excavation complete, attention is now turning to shaft- and tunnel-lining operations. Tunnel lining commenced late last year in the already-completed drives and consists of the installation of fiberglass reinforced plastic (FRP) pipes within the excavated tunnel using a low-strength grout backfill. John Holland, the contractor, has installed approximately 10% of the tunnel liner pipes to date. Shaft lining is scheduled to begin late March at the L.E. Cotchin Reserve Shaft. Because of a recent design change request, the final lining for this 40-meter (130-foot) deep shaft has approximately 25 meters (80 feet) of unreinforced concrete.
The two-stage NSP, developed jointly by Melbourne Water and Yarra Valley Water, involves construction of approximately 12.5 kilometers (8 miles) of new sewer under the northern suburbs of Melbourne, Australia. This will increase the capacity of the existing sewerage system and help to protect local creeks. Working with Sinclair Knight Merz (SKM), Jacobs Associates led the tunnel and shaft design on both stages of the project and is now providing construction support services as the owner’s design representative. The construction partner for both stages is John Holland.
Additional news, videos, and photographs are available on the project’s website at http://www.nsp.net.au.
