HDD Water Line Relocation For Tunnels Project

May 2014, Vol. 69 No. 5

Mears Group Inc. successfully relocated a raw water line for Skanska, Kiewit and Weeks, known as SKW Constructors, in 2013.

The group contracted with Elizabeth River Crossings OpCo LLC as the design-build contractor for this public-private project with the Virginia Department of Transportation in the city of Norfolk, VA. The project consisted of installing an internally and externally coated 36-inch steel pipe for raw water transmission under the Elizabeth River using horizontal directional drilling (HDD) methods at the 4,500-ft long crossing, as well as installing ductile iron pipe using open-trench methods on the land portions with tie-ins to the existing raw water line.

The existing Midtown Tunnel is a two-lane tunnel under the Elizabeth River connecting the cities of Norfolk and Portsmouth. This expansion project will add a new two-lane tunnel running parallel to the existing one – dedicating eastbound traffic for one tunnel and westbound for the other to increase the capacity for traffic between both cities. Prior to the tunnel construction (which requires dredging technique to install precast tunnel sections), the existing raw water line needed to be relocated. Throughout the duration of this project, the city of Norfolk was able to provide uninterrupted water service to local residents.

Mears was selected to handle the water line relocation portion of this high profile project which included a tight construction schedule and challenging drilling geometry. As the sub-contractor, Mears supervised activities related to the onsite fabrication and handling of the HDD pipe by Patterson & Wilder, and the open-trench ductile pipe installation by TA Sheets, in Portsmouth and Norfolk.

Mears’ crews mobilized in December of 2012 to install 60-inch casings on the entry and exit sides of the river crossing to mitigate the inadvertent return of drilling fluids in the upper strata of softer soils and isolate the problems with drilling through fill material. Once the casings were installed and reamed out, centralizers were installed to maintain the drill string in the centers of the casings during pilot hole operation, as well as subsequent reaming passes.

Drill begins

Pilot-hole activities started in January, with 48-inch diameter reaming activities finishing in March. The geometry of the 4,470-foot drill included two horizontal curves to circumvent existing and proposed structures within the new raw water line easement. The pilot hole was drilled using the intersect method – drilling from both the entry and exit sides and meeting beneath the Elizabeth River.