Balancing Pipe and Backfill Requirements in Difficult Installation Conditions

Engineers provide the best service to their clients by optimizing the cost of projects without affecting the quality or performance. Since buried pipe performance is the result of interaction of both the pipe and the surrounding soil embedment, projects involving buried pipes require careful decisions in selecting both the pipe and the backfill to provide owners with quality projects at appropriate costs. Design decisions on pipe and backfill can become even more important when difficult ground conditions are encountered. Increasing pipe strength or stiffness may appear to be an appropriate step to address this situation, but ignoring backfill and construction issues may mean that the overall reliability of the project is not increased, or that optimum cost is not achieved. This paper presents a case study of a significant fiberglass pipe installation in soft native soils. Evaluation of native materials, available pipe materials, and construction procedures led to a design decision to use pipe with a stiffness of 18 psi (124 kPa), along with a carefully monitored construction process. Topics discussed include native soil conditions, pipe specifications, and available backfill materials. The paper demonstrates a rational process by which engineers can evaluate the relative benefits of modifying backfill materials, pipe strength or stiffness, or construction practices to achieve the most economical results for a client. The project was completed successfully meeting both quality and performance requirements.