Innovative Auger Boring Sewer Rehabilitation Project to Renew a Century Old VCP Combined Sewer at Over 30-ft Depth

Innovative Auger Boring Sewer Rehabilitation Project to Renew a Century Old VCP Combined Sewer at Over 30-ft DepthAbstractThe Pittsburgh Water & Sewer Authority (PWSA) engaged Mott MacDonald to provide engineering and design services for the rehabilitation of an aging 24' VCP Combined Sewer, which had served the community for over a century. The challenges we faced were twofold. Firstly, the sewer had deteriorated significantly, exhibiting cracks, deformations, and signs of impending collapse. Its unique alignment within a meandering stream bed, subsequently backfilled to a depth of over 30 feet, presented complex design and construction obstacles. Secondly, this combined sewer played a vital role in handling both sanitary and stormwater flows, making it imperative to maintain uninterrupted service during the rehabilitation process. Traditional CIPP lining methods were deemed inadequate due to the sewer's extensive defects, posing a warranty risk. Mott MacDonald devised an innovative solution: an auger bore trenchless sewer installation to replace the existing sewer minimizing the impact to the surroundings. This approach involved two open excavation pits to install the auger bore, launching it in both directions. The downstream bore reached a depth of approximately 36 feet, connecting to an existing brick manhole via hand tunneling. A 36' diameter steel casing pipe was installed as part of the boring process, within which a 24' HDPE Carrier pipe rested on spacers. Grouting filled the annular space, ensuring a secure and lasting solution. The construction progressed successfully meeting the accelerated schedule, showcasing the effectiveness of our innovative approach. The auger bore cored through the existing VCP sewer at a crossing point without complications. To maintain uninterrupted sewer flows, we implemented strategic bypass pumping. Additionally, we introduced a new service lateral with an inside drop connection, reducing excavation depth and minimizing disruption to the community. In conclusion, Mott MacDonald's auger bore design offers a blueprint for addressing complex sewer rehabilitation challenges. Our project not only rejuvenated critical infrastructure but also underscored our dedication to sustainable engineering solutions. We eagerly look forward to sharing our success and insights with the engineering community, where we believe our innovative approach will inspire water and wastewater providers to consider innovative solutions in complex situations.This paper was presented at the WEF Collection Systems and Stormwater Conference, April 9-12, 2024.SpeakerLenner, JeffPresentation time09:30:0010:00:00Session time08:30:0010:00:00SessionTrenchless InstallationSession number27Session locationConnecticut Convention Center, Hartford, ConnecticutTopicBypass pumping, Combined Sewer Overflow, Combined Sewer System, Construction, Cured-In-Place Pipe Assessment, Design considerations, Rehabilitation, Trenchless TechnologyTopicBypass pumping, Combined Sewer Overflow, Combined Sewer System, Construction, Cured-In-Place Pipe Assessment, Design considerations, Rehabilitation, Trenchless TechnologyAuthor(s)Lenner, JeffAuthor(s)J. Lenner1, T. Stutzman2Author affiliation(s)Mott MacDonald 1; Pittsburgh Water and Sewer Authority 2SourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Apr 2024DOI10.2175/193864718825159369Volume / Issue Content sourceCollection Systems and Stormwater ConferenceCopyright2024Word count19