DC Water at Work: Using a Composite Liner Design to Rejuvenate the Service Life of Large Sewer Tunnels

As a municipal client, we see a lot of support for standalone structural liner designs, however much less support is given to its alternative, “composite liner design.” It’s easier said than done in engineering a standalone structural liner to retrofit a sewer tunnel constructed more than a century ago. The “fully deteriorated” definition by NASSCO has been proved easily controversial, subjective, and difficult to apply to large diameter sewers, and hard on sustainability, hydraulically, and financially. We need to spend within the means of the owner as professionals that fix pipelines for a living, instead of replacing pipelines for a living as the expensive “low-hanging fruit.” In the indefinite life of huge arched sewage tunnels, its continuous life comes from the continued capability of additional deformation without compromising its compression-ring stability. A composite liner may suffice in achieving that because it works with the host tunnel’s in situ strength that remains indefinite.