Advancing Cut and Cover Tunnelling in Auckland –Experience Gained from New Lynn Rail Trench

摘要

KiwiRail has a goal of signifi cantly improving passenger rail services to west Auckland, as part of itsrnDART (Developing Auckland’s Rail Transport) suite of projects. The New Lynn Rail Trench (NLRT)rnproject was a signifi cant component of this work. The NLRT project facilitates essential doubletrackingrnof the Western Auckland line, and provides a new commuter transportation hub within arnbusy town centre.rnThe 1.5 km stretch of track through the New Lynn town centre has bisected the township for overrn80 years. Double-tracking the line provided the opportunity to grade-separate road and rail, whichrnwould help to re-connect both sides of the township and enhance public amenity and safety.rnKiwiRail employed an Early Contractor Involvement (ECI) procurement model engaging arnconsortium comprising Fletcher Construction, Beca Infrastructure and Synergine to develop arnDesign and Construct solution.rnWith weak soil conditions and high groundwater levels, a diaphragm wall construction method tornform the trench walls was selected as the best solution. Further challenges to construction includedrnworking within a narrow rail corridor constrained by buildings along much of the boundary, andrna requirement to keep the existing line open for rail services. Detailed construction planning wasrnrequired to ensure rail and construction safety in a constrained space whilst building the trenchrnwalls, propping these walls during excavation, and constructing the base slab in the most effi cientrnway possible.rnThis paper will detail the geotechnical conditions and the additional constraints that made thisrnrail trench a challenging structure to design. It will also describe the fi nal design and constructionrnmethodologies that were employed, that allowed very successful completion of the project.rnAdditionally, this paper will review the design and construction lessons applicable to therncurrent Victoria Park Tunnel project, and indeed for all future cut and cover tunnel projects in thernAuckland isthmus.