Project At-a-Glance
- Trenchless installation of fused 42-in HDPE pipe across the James River
- 5700-ft of pipeline installed beneath the active 55-ft deep Newport News Ship Channel.
- Design-Build project delivery
Hampton Roads Sanitation District (HRSD) has embarked on their innovative Sustainable Water Initiative for Tomorrow (SWIFT) program to protect the environment of the Chesapeake Bay, enhance the reliability of the long-term water supply of Hampton Roads and mitigate sea level rise and saltwater infiltration in the aquifers. The HRSD is closing the Boat Harbour WWTF in Newport News, expanding the existing Nansemond Treatment Plant in Suffolk, and installing a large diameter force main across the historic James River between the plants. The wastewater force main pipe is 42-in to 54-in diameter HDPE pipe. The 4.5-mile pipeline includes a section of about 1.1 miles of Horizontal Directional Drilled pipeline beneath the active 55-ft deep Newport News Ship Channel.
The Design-Build team of Garney Construction and Dewberry Engineers was engaged by HRSD to design and build this force main which includes short sections onland at both shorelines. Located close to the mouth of the James River where it drains into the Chesapeake Bay, the soils underlying the river in this area are geologically recent, poorly consolidated and very soft marine sediments that provide minimal strength and pipeline support. Accurate characterization of the subsurface materials was therefore critical for assessing optimal burial depth, pipeline support, and marine installation methodologies.
Brierley personnel held several key roles on the design/build team as the HDD and geotechnical specialists. Brierley was responsible for developing the geologic interpretation and overall site characterization based on the Owner-produced Geotechnical Data Report, preparing 30% to 100% HDD design packages, and preparing one-dimensional and three-dimensional Finite Element Modeling (FEM) of anticipated short-term and long-term settlement of the soft surficial sediments related to the planned trenched pipe installation methods.
Brierley also planned, subcontracted, managed and performed supplemental geotechnical programs both on the north shore at Newport News and additional overwater deep borings for the revised alignment of the HDD and pipe casing design to the south of the shipping channel. These supplemental studies provided critical inputs to the transition between the onshore trenched portion of the pipe and the HDD component as well as geotechnical parameters key to HDD design including pipe buckling, pipe pullback forces, and hydrofracture assessment.
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