PRESCRIPTIVE SPECIFICATION DESIGN: THE IMPACT ON COST AND CONSTRUCTABILITY – CASE HISTORY

摘要

This paper outlines how specification driven design has made Toronto Area transit infrastructure projectsmore expensive than similar private projects, and provides a case study of the results of an excavation atLaunch Shaft 1 (LS1) for the Eglinton Crosstown Light Rail Transit project in Toronto, Ontario. Thepaper will describe the impact specification driven design parameters can have on design economy,constructability, and schedule and will suggest an alternative approach utilizing the ObservationalMethod. As a result of the initial specification based design, Isherwood was retained by both the GeneralContractor and the Specialty Excavation Shoring Contractor to provide value engineering leveraging theObservational Method to improve constructability and construction schedule. By using well known,accepted design methods coupled with local experience in lieu of the specified design pressures andparameters, the redesigned bracing scheme reduced construction cost and schedule. This excavation casehistory can be a lesson learned for future transit projects.