Design-Build Project Delivery for Sewer System Rehabilitation

This paper presents a case-study of a design-build project to rehabilitate 80,000 linear feet (LF) of small diameter sewers over a 20 mile square area on a large military base. The design-build process created a strong team effort among the engineer, contractor, subcontractors and owner.In order to rehabilitate a portion of its sanitary sewer system, a Government agency decided to utilize a design-build delivery. By selecting this approach, the same team could conduct the closed-circuit sewer inspection (CCTV), determine the necessary repairs and repair methods, perform value-engineering of the proposed rehabilitation, and complete the construction work all on going over two years. Construction activities were limited by numerous environmental constraints, traffic control issues, and coordination with residents and military activities.The design-builder prepared a cost proposal based on the existing CCTV and other information provided by the Government. The CCTV was five years old and partially incomplete. It was expected that conditions had changed, an issue that needed to be addressed in the early stages of the project. After the project was negotiated, the design-builder retelevised all pipeline segments to refine and update the scope of work and find the means to best-value alternatives to rehabilitate the system at a cost consistent with the original negotiated fee.A matrix-approach was developed to determine cost effective solutions at each site. Cured-inplace piping (CIPP) became the selected alternative to repair much of the existing cracked vitrified clay pipe and cured-in-place spot repairs were completed where only a portion of a sewer segment required rehabilitation. Open trench repair was performed for pipe sags, collapses or other major defects.This paper discusses the advantages and disadvantages of the design-build delivery method in regards to large conveyance projects. The case study will demonstrate that the project approach allowed the design-builder flexibility to adapt the project to existing site conditions within the original project budget. By having the contractor and engineer on the same team, the engineer could more easily review the sewer inspection videos and develop the scope of work while the contractor looked at constructability issues. The engineer collaborated with the contractor when alternative construction approaches were proposed to ensure the original design intent was still satisfied. This design-build delivery method also allowed the design-builder the flexibility to evaluate the use of newer technologies including the use of ultraviolet light cured CIPP.