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Marginal Interceptor Rehabilitation

  • Marginal Interceptor Rehabilitation
  • Marginal Interceptor Rehabilitation

The Somerville Marginal Interceptor is an 85-inch by 90-inch brick combined sewer constructed in the 1890s to convey combined sewer flows from wards one and three to the Mystic River. It now conveys combined sewer flows to the Massachusetts Water Resources Authority’s (MRWA) Somerville-Medford Branch Sewer and combined sewer overflows (CSOs) to MRWA’s Marginal Primary Treatment Facility.

Subsequent Construction and Highway Loads

Approximately 60 years after construction of the interceptor, McGrath Highway was constructed, with the Sommerville Marginal Interceptor situated under the center northbound lane. Introduction of highway loads and the method of construction of the original access structures led to the development of a continuous longitudinal crack at the pipe crown, extending between access structures, and deflection of the crown arch, indicating incipient failure.

Analysis and Recommendations

Kleinfelder performed cleaning, removing almost 300 tons of debris, and multi-sensor inspection of the Interceptor to support an analysis of rehabilitation alternatives. The project team ultimately recommended a sprayed-in-place cementitious liner to reinforce the pipe barrel, and internal reconstruction of the access structures to transfer traffic loads from the pipe crown to the piles and soil sub-grade supporting the pipe.

Project Results

Kleinfelder’s solution met the City’s need for a full structural rehabilitation of critical infrastructure, while also satisfying key stakeholders. Disturbance of the highway was minimized by eliminating excavation and allowing all work to be performed overnight. Impacts to MWRA’s CSO operations were managed by minimizing reduction of the storage volume.

Project Details

Somerville, MA
City of Somerville

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