York Street Sewer Pump Station

Springfield, Massachusetts needed a new pump station to transfer wastewater from the community to the Springfield Regional Wastewater Treatment Facility across the Connecticut River. Existing infrastructure wasn’t keeping up with the region’s growing needs, and a proposed $115 million project would convey approximately 70 percent of the region’s wastewater across the river for treatment via three new wastewater pipes. GeoEngineers’ staff provided geotechnical recommendations for excavation support and temporary structural design for the project.

The deep excavation pits required for the project, and their proximity to existing infrastructure and the Connecticut River, presented a number of geotechnical challenges. Designers opted to use a pipe jacking approach to install the three new wastewater pipes beneath a set of railroad tracks. Pipe jacking uses powerful hydraulic jacks to thrust pipeline through soil formations in a straight line. Unlike horizontal directional drilling, which can drive pipe from the surface and beneath obstacles along a curved path, pipe jacking must take place in deep excavation pits at the installation depth of the pipeline.

Approach

SOE Redesign

Our team quickly realized that each of the project’s five major excavations were unique—and each support of excavation (SOE) design had to meet specific needs and conditions. During contract review, the team found serious issues with the prescribed 35-foot-deep secant pile jacking pit required for pipe installation. The jacking pit was not constructible based on the proposed geometry of the proposed 72” and twin 48” pipes. The original design called for the pipes to enter the excavation at a skew, causing large and structurally insufficient wall penetrations within the secant pile excavation wall. The team re-evaluated the originally prescribed secant pile support system and piping layout and provided a slurry wall SOE with two levels of internal steel bracing that was robust and effective enough for the large proposed pipe openings.

The team also saw a creative opportunity to improve project efficiency through more robust excavation support. Originally, the project team planned to install the new lengths of wastewater pipeline before the associated pump station due to concerns about pipe jacking forces harming the new structure and equipment. GeoEngineers found a way to speed up construction and safely install the pipeline after completing the pump station. The team protected the pump station’s infrastructure from jacking pressures with T-panels embedded into the underlying bedrock along the jacking wall. This design provided additional wall stiffness and saved the client time and money.

Support for Levee-Crossing Bulkhead

The 72” and twin 48” wastewater pipelines that would carry wastewater across the Connecticut River for treatment needed to cross sensitive levees on either side of the river. Our geotechnical team designed shoring systems for the levee-crossing bulkhead to allow access for the future open cut excavation and installation of the pipelines. In total, the team designed 130 linear feet of bulkhead, secured by threaded tie rod to a sheet pile deadman shoring system.Temporary Structural Design

Temporary Structural Design

The team also provided structural concrete design for an additional wastewater diversion structure, a design for cantilevered soldier pile shoring to support the excavation and a temporary work trestle that will extend approximately 100 feet into the Connecticut River and allow a crane to move out over the river to support construction.

Results

Our geotechnical and temporary structural design work supported construction for the York Street Sewer Pump Station project—all while reducing costs. Thanks to the combined efforts of the project team, the City of Springfield will soon have a drastically upgraded wastewater system providing sewer overflow reduction, climate resilience, system redundancy and reliable infrastructure for decades to come.