Belmont Light, Underground Transmission Line

Cambridge and Belmont, MA




2019 Engineering Excellence Silver Award, American Council of Engineering Companies of Massachusetts
Belmont Municipal Light Department Underground Transmission Line
Belmont Municipal Light Department Underground Transmission Line

Belmont Municipal Light Department (BMLD) needed to upgrade their aging substation and power distribution system to improve reliability and prepare for future demands. Working with Eversource, the area’s electric service provider, BMLD oversaw construction of a new substation in Belmont and a 0.8 mile, 115kV transmission line between the new substation and the existing Eversource substation in Cambridge. SGH provided civil and geotechnical consulting services associated with alignment design and construction of the underground transmission line.

Scope | Solutions

The transmission line’s alignment was complicated due to site constraints, performance requirements, and its five crossings at important infrastructure, each with unique subsurface conditions affecting installation and soil stabilization considerations. Highlights of our work include the following:

  • Evaluated trenchless technologies for installing the transmission line to determine the best option for the project

  • Designed temporary support-of-excavation and concrete encasements where the transmission line came within 25 ft of active Massachusetts Bay Transportation Authority (MBTA) rail tracks

  • Designed a concrete mat supported on helical piles to minimize settlement in two areas with deep layers of soft organic soils

  • Collaborated with the owner’s team to obtain approval from utility owners (City of Cambridge, City of Cambridge Water Department, and Massachusetts Water Resources Authority), the MBTA, and the City of Cambridge Conservation Commission

  • Prepared construction documents, including temporary erosion and sedimentation controls, site plans and profiles, underground civil structures (e.g., manholes), temporary excavation support, dewatering, helical piles, provisions for performance-based design of trenchless technologies, and site restoration

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