Deep tunnels: Never maintenance-free

Most sewage and CSO deep tunnels have pump station facilities that are often equipped with screening and air and odor management facilities. The flows are then directed to water resource recovery facilities (WRRFs) and high-rate treatment systems for treatment and eventual return-back to surface waters and/or reuse facilities. In the case of deep tunnels dedicated to flooding and stormwater...

When Singapore PUB began the design of their Phase 2 Deep Tunnel Sewerage System (DTSS) project, they wanted to know the condition of their Phase 1 tunnel, which had been in operation for 10 years. When asking the operations team how the tunnel looked, they were shocked to get the response that this tunnel was “maintenance-free” and had no access points.

One of the biggest challenges for utilities is how to inspect and access these large-diameter tunnels. While many are aware of the tunnel’s presence during design and construction, once in the ground, tunnels can sometimes become a forgotten infrastructure due to their long service life and sometimes infrequent use. Because of this, many tunnels are not frequently accessed or inspected, and...

A concern that utilities have throughout tunnels is the buildup of sediment, debris, grit, and floatables. While all debris and grit must be dealt with, floatables are an important consideration because if not flushed through the systems, they can form a mat on the surface of the water. This could interfere with real-time control equipment or could eventually sink during dewatering and leave...

Faruk Oksuz is the vice president and director of infrastructure systems and civil works at Black & Veatch, based in Chicago, Illinois, United States. Brianne Nakamura is the senior manager of technical programs at the Water Environment Federation, based in Alexandria, Virginia, United States.