What's the True Cost of Rehabilitation? – Calculating Lifecycle Costs for Trenchless Technologies in Portland, Oregon

摘要

The Taggart Outfall 30 is one of the longest-serving large diameter sewer pipes in the City of Portland. The 7,600 LF, 66-120" brick sewer was constructed in 1906 to replace cesspools and reduce the death rate from typhoid fever and other infectious diseases in the densely settled neighborhoods. At the time, it was the largest diameter and most expensive sewer Portland had constructed with an initial budget of $250,000. Over the past century, the City's Bureau of Environmental Services has utilized this asset with multiple tie-ins, diversion structures, and retrofits that allow the tunnel to function today as a critical piece of the combined sewer infrastructure as collection and overflow. As part of their proactive approach to asset management, the City identified the Taggart Outfall as a candidate for rehabilitation to extend the life of the asset and maintain the system for the years to come. This paper will review the background, preliminary design & alternatives analysis with discussion on the unique structural and geotechnical considerations and a description of the lifecycle net benefit-cost ratio (nBCR) method.