MFS Consulting Engineers & Surveyor, DPC was contracted by POWER Engineers, Inc. to provide professional geotechnical and structural engineering services in support of the Eversource Andrew Square to Dewar Street Trenchless Crossings project in Boston, Massachusetts.
The overall project is comprised of the construction of a new 2.1-mile 115kV underground transmission line connecting the Andrew Square substation to the Dewar Street substation in Dorchester and South Boston, Massachusetts. As part of the project, two (2) trenchless crossings were required; one using an existing area bridge and the other using a microtunnel beneath an MBTA and MassDOT rights-of-way.
MFS prepared a subsurface investigation plan for the required subsurface investigation to inform the project design. The subsurface investigation was carried out by others and the results were provided to MFS for review and to inform the trenchless crossing designs.
MFS prepared a design package for the microtunnel crossing to include the design of the jacking and receiving pits, design of the casing using both steel and HOBAS materials, and determined the anticipated maximum forces in the casing. MFS prepared construction documents including plan, profile, and detail drawings as well as specifications for the microtunnel trenchless crossing.
MFS’ structural team provided the support of excavation (SOE) design for the jacking and receiving pits for the microtunnel beneath the MBTA and MassDOT rights-of-way. Due to varying subsurface conditions at both pit locations, two (2) types of SOE systems were designed. The receiving pit SOE was comprised of driven sheet piles with an internal waler and strut bracing system, and the jacking pit SOE was comprised of drilled pipe piles with an internal waler bracing system. Additionally, MFS provided the utility support design for the existing electrical utilities that were exposed during the excavation for the receiving pit.
MFS’ structural team also provided the utility crossing design at the Patten’s Cove Bridge Crossing. The Patten’s Cove Bridge is comprised of a reinforced concrete jack arch bridge superstructure with an asphalt topping supported by reinforced concrete abutments at either side of the bridge span. The Patten’s Cove Bridge Crossing consisted of demolishing a portion of the existing median slab and reconstructing the median embedded with the new conduits. MFS provided a structural analysis of the jack arch bridge to ensure it could support the thicker median slab. MFS prepared the Final Construction Document set, including construction notes, SOE and Bridge Crossing plans, sections, and details.