There are more than 150,000 potable water systems throughout the US, with more than two million miles of buried pipeline. Many were installed in the early-to-mid 20th century and are now 75 to 100 years old. Currently, six billion gallons of water are lost daily through infrastructure issues. This webinar focused on buried large diameter water transmission pipelines. Presenters provided an overview of water conveyance systems and discussed design and installation of welded steel water pipe. Topics include a discussion of asset management through technologies that enable condition assessment of prestressed concrete cylinder pipe (PCCP) systems as well as trenchless renewal methods to rehabilitate distressed pipe.
Transmission lines carry large quantities of water from a source of supply to a treatment plant and on to distribution systems. Sizes can range from 16 to more than 200 inches in diameter. Materials include steel, concrete, ductile iron and fiberglass pipe.
Topics discussed include:
Alignments for large diameter pipelines pose a significant challenge. They often traverse urban sprawl with significant development, streets with congested utilities, and established transportation networks. Traditional alignment studies identify several corridors for consideration, but engineers have found that small adjustments can result in millions of dollars in savings.
Use of computational techniques can help identify the best route based on optimum parameters that could minimize impacts to commercial or residential developments, traffic patterns, sites of known contamination, large utility crossings, environmentally sensitive areas, etc. The corridor can then be broken down in a series of network links with each segment scored separately using weighted criteria based on project-specific parameters. Analytical programs are used to evaluate all segments and identify the most desirable alignment with its associated cost and time to complete. An alternative method focuses on geospatial analysis using stacked layers of publicly available information including population densities and traffic.
Risks such as the potential for pipe failures due to water hammers or conflicts with existing utilities should be identified and mitigated during large design. Established transient models will identify surge pressures that can be incorporated into the pipe’s design parameters. An extensive subsurface utility engineering program can identify and confirm the location of utilities not shown or incorrectly located on as-builts.
Valve selection, installation techniques and testing play a critical role in minimizing future leaks.
Construction approaches include open cut and tunneling. Open cut requires extensive shoring and often results in slow production rates in urban areas. Proper handling of pipelines can minimize damage during installation. Manufactured materials are nearly always used to embed the pipe for maximum pipe support. If properly embedded, the pipe should not deflect at all when loaded.
Tunneling is used extensively for large diameter projects where open cut is not practical. Tunnel Boring Machines or TBMs may include digging shields, open-faced tunnel boring machines or closed-faced tunnel boring machines.
Inspection is required prior to in-service usage to document proper welds, liner thickness, and no cracking in the mortar lining.
Asset management is critical to maintain and support infrastructure networks. Ruptures of large diameter pipes result in significant property damage, loss of life and service disruption to a significant number of customers. The key is prioritizing repair and determining maintenance methods based on risk and cost analyses. Risk is determined by determining the current condition of pipelines, through state-of-the-art condition assessment tools, and knowing the consequence of failure. It is then possible to decide whether a localized or comprehensive repair should be employed. The goal is to forecast and subsequently prevent failure through selection of the appropriate rehabilitation, which could include:
- Carbon Fiber Reinforced Polymer (CFRP) Repair
- Post-Tension Tendon repair
- Steel-Cylinder Relining
- Steel Cylinder Sliplining
- Removal and Replacement
For more information, feel free to reach out to our presenters: