In 2018, the city of Mobile, Alabama began a project to upgrade an existing 36’’ and 42’’ trunk sewer into a new 11,000 ft, 60’’ diameter gravity trunk sewer main. The upgrade would involve a segment of the pipe that starts on the south side of Three Mile Creek before crossing over ending at a Severe Weather Attenuation Tank. The upgrade was important to provide the needed transmission and storage capacity to reduce the occurrence of sanitary sewer overflows during rain events.
One of the main design challenges with this project was determining the constructability of the proposed upgrades due to the size of the pipe and structures. In the areas where the pipe would be installed, there were site constraints that limited the length of pipe that could be installed as well as the available the working space required for installation.
To overcome installation constraints, engineers utilized two sizes of AGRU HDPE pipe, which provided enough flexibility to allow the contractor to complete the installation while also managing the site constraints. Horizontal directional drilling (HDD) was used as the installation method.
Additionally, because some segments of the existing could not be increased in diameter, the engineer designed a solution that utilized sections of 48” and 63” diameter pipes in SDR 11. AGRU was the only manufacturer that could provide products that met this requirement.
The project’s construction is ongoing, but the contractor has been able to successfully install the pipes without issue. Furthermore, the engineering team’s choice of piping product and installation approach have already provided significant time savings as the alternative would have been tunneling under the creek. Once completed, this project will become the largest OD HDPE HDD project in North America.
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