M Street Diversion Sewer, Division E

Client

DC Water

Location

Washington, DC

Key Challenges & Project Details

  • Consent decree project is part of the “Clean Rivers” Program enabling DC Water to reverse the combined sewer flow from approximately one third of Washington, DC’s systems from East to West to West to East.
  • The reversed flow is carried within a new 48 in., 974-ft. long and 108 in., 1,315-ft. long sewer installed using trenchless excavation by a tunnel boring machine.
  • Flow from the tunnels is deposited in a cast-in-place 7.5-ft. wide X 15.5-ft. high (277-ft. long) concrete approach channel and into the main tunnel shaft.
  • Supported and protected a 72 in. turn-of-the-century brick sewer where it crosses through the lower approach channel and a large diameter Washington Gas main.
  • Several shafts and the approach channel were excavated to 61-ft. deep and were constructed of a contractor-designed soldier beam and lag support system with cross lot bracing up to five levels.
  • Work was within active roadway and limited amounts of open areas.
  • To access the existing ESI Sewer, three shafts were constructed up to 50-ft. deep within a busy travel-way of M Street using the elliptical configuration. Shafts were precisely centered on the existing sewer and required contractor-designed supports of gas, water and duct bank with enclosures for construction protection.
  • Relocated two duct banks that conflicted with new CSO structures and coordinated relocating overhead Pepco and Verizon lines to allow access to install the support of excavation soldier pile and lagging.