Case Study:Texas Municipality Diverts Flow in Large Diameter Sewer Lines

By: Brandon Dalton

Customer

In the past few years, there have been several sewer line rehabilitation projects in Texas involving large diameter sewers (6 feet to 11 feet diameter) located 50 feet to 60 feet below ground. These projects have either required the city to block flows in order to divert to other sewer lines during construction, or, to block flows for leak testing of newly rehabilitated sewer lines. 

Challenge

Finding a way to block off large diameter sewer lines when they were so far below ground presented a challenge. One of the stop log applications involved installing a sewer 11-feet in diameter, located 60 feet below ground. In order to install the solution, crews needed access to a sewer line located in a shaft in the middle of the street. There were no immediately adjacent city facilities where the stop logs could be stored.

Solution

Plasti-Fab engineers developed a plan to build a stop log system that could be stored in the shaft when not in use, which was based on a design used for the same municipality on a project with a smaller sewer line. Plasti-Fab’s composite stop logs are the perfect answer for this because of their corrosion resistance.

However, engineers informed Plasti-Fab that when the stop logs are installed, and the sewer line is blocked, the water could back up as high as 30 feet in the shaft behind the stop logs. This much head pressure on a stack of stop logs would require a tremendous amount of lifting force to move the stop logs.

In order to reduce the amount of lifting force, Plasti-Fab designed the bottom stop log to include a sluice gate. The sluice gate would open and allow the built-up water to drain before trying to lift the entire stack of stop logs.

The design included additional stop logs that would stack on top of the bottom log to create an overall height of 31 feet of stop logs.

The sluice gate on the bottom stop log was built with two attachment points to connect a stainless steel lifting cable. To raise the stop logs, the lifting cable would be pulled from above to open the sluice gate. Once the water on the upstream side of the stop logs drains down, the same lifting cable is pulled from above a total of 11 feet. This lifts the entire stack of stop logs clear of the sewer line. The lifting cable was made with loops towards the top that allow the cable to hook onto anchor assemblies installed at the top of the shaft. Therefore, once fully opened, the lifting cable can hook onto the anchor assemblies and the stack of stop logs stays suspended in place (within the guide frame) until it needs to be used again. Installation is done in the opposite order, and the sluice gate closes under its own weight to block off the flow.

Results

The design team at Plasti-Fab was able to provide a unique stop log design that not only met the immediate need to block flow but also provided a corrosion-resistant solution that could withstand the harsh environment of a sewer collection system for years to come.

About CC Lynch

C.C. LYNCH & ASSOCIATES, INC. has been in continuous operation since 1966. Founded by Chuck Lynch and wife Barbara “Babs” Lynch the company has operated as a manufacturer’s sales rep firm specializing in water and wastewater monitoring instrumentation since the early 1970’s. Beginning in 1992 the company ownership was sold by Chuck and Babs Lynch to sons Malcolm and Kelly Lynch and friends Trey Campbell and Russell Park. Chuck Lynch continued with C.C. Lynch & Associates, Inc. as the CEO until he passed away in 1999. Babs Lynch continued working at C.C. Lynch until she passed away in 2009. In 2001, C.C. Lynch & Associates, Inc. acquired Environmental Monitoring & Sampling Instruments (EMSI) of Houston, Texas. Our central office is located in Pass Christian, Mississippi and we maintain regional offices in Lafayette, Louisiana, Mobile, Birmingham, Baton Rouge, Houston, Austin, and Dallas, Texas.

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