Construction of the Largest Solid Wall HDPE Outfall in North America - McLoughlin Point WWTP Outfall, Victoria B.C.

摘要

AECOM and its Joint Venture partner Graham Construction (AGJV) designed and facilitated construction of a new ocean outfall as part of the new McLoughlin Point Wastewater Treatment Plant in Victoria, B.C. The 1.92 km (1.2 mile) long outfall was primarily constructed with 2250 millimetre (88.6 inch) DR26 High Density Polyethylene (HDPE) pipe which is the largest solid wall HDPE outfall in North America.The inshore section from the new treatment plan to the ocean consisted of a 120-metre (394-ft) long, “wet-exit” microtunnelling drive was constructed with a 2120-millimetre (6.95-feet) steel pipe section driven through highly abrasive granodiorite bedrock. The drive started from an inshore blasted jacking shaft at a depth of approximately 12 metre (40 feet) below ground, to a blasted offshore marine trench at a water depth of approximately 12 metre (40 feet). This section of pipe was installed by a Herrenknecht AVN MTBM.The offshore section of the outfall was comprised of concrete weight ballasted 2250 millimetre (90 inch) HDPE pipe, installed by “float and sink” methods, in water depths up to 62 metre (203 feet) deep. The float and sink installation was approximately 1800 metre (5900 ft) long, and includes a 210-metre (690-feet) long, 36 port diffuser. The 2250 millimetre (88.6 inch) HDPE pipe consists of a short inshore section of DR 21 pipe (107 millimetre (4.2 inch) wall), and the balance being DR 26 pipe (87 millimetre (3.4 inch) wall thickness). This is the largest deployment of solid wall HDPE and the largest solid wall HDPE outfall in North America.This paper will discuss design and construction details for the microtunnel as well as the landmark float and sink process for the largest solid wall HDPE outfall in North America.