2014 - Washington, D.C.
The project site is located on First Street NW across from McMillan Reservoir in Washington, D.C. The purpose of this project is to provide support of excavation for the Channing Street Mining Shaft, which will be an entry point for a tunnel boring machine. The work consisted of the construction of a reinforced concrete slurry wall shaft that will allow a tunnel boring machine to be lowered 150ft into the excavation, in conjunction with cement-bentonite cutoff wall to limit water infiltration at the head of the underground tunnel to begin the tunnel mining process. Once complete, the tunnel will increase storm water discharge capacity for neighborhoods north of Capitol Hill.| Owner | DC Water and Sewer Authority |
| Design Builder and Construction Manager | Skanska-Jay Dee Joint Venture |
| Geotechnical Engineer | Parsons Brinckerhoff |
| Structural Engineer | Parsons Brinckerhoff |
The slurry wall was constructed using the tremie concrete method, with thickness of 42” to provide adequate strength to retain soil during mass excavation. It used over 200 tons of both steel and GFRP (Glass Fiber Reinforced Plastic) bars, and 6000 cubic yards of concrete.
The slurry wall was constructed with various “soft eyes” where the tunnel boring machine will bore through to begin tunnel excavation. GFRP bars were used in place of traditional black steel at pre-determined locations to accommodate slurry wall opening requirements for the tunnel boring machine.
Due to the depth required for this project, maintaining verticality of excavation is the most important aspect for a quality product, as such multiple technologies were used to monitor the deviations of the panel.