A River Runs Through It: Force Main Relocation Across the Neuse
Prepared for the 2014 NC American Water Works Association & Water Environment Association (AWWA-WEA) Annual Conference by Ben R. Latino, Jr., PE, and K. Jason Savage, PE
Read the full white paper
Abstract
The purpose of this paper and presentation is to discuss the challenges encountered and solutions developed for the relocation of a wastewater force main across the Neuse River that involved portable dams, open cut installation, and in-water construction moratoriums. A 12-inch steel force main owned by the City of Raleigh Public Utilities Department (CORPUD) was attached to the Auburn-Knightdale Road bridge (Bridge No. 237). North Carolina Department of Transportation (NCDOT) is currently designing a replacement for that bridge, and requested that CORPUD permanently relocate its force main to allow demolition and construction of the bridge replacement. Reattaching the force main to the new bridge structure was not an option allowed by NCDOT.
McKim & Creed was contacted by the CORPUD to perform an expedited evaluation of alternatives for the project and determine an appropriate method for relocating the force main within the timeframe established by NCDOT. Relocation alternatives included new installation by horizontal directional drill (HDD), bore and jack, microtunnel, aerial installation with truss and piers, and open cut installation. Although trenchless methods such as HDD were very attractive for both scheduling and environmental considerations, longer replacement length, increased construction costs, and higher risks due to the geology reduced the feasibility of these installation methods.
Ultimately, an approximately 200 LF open cut installation with partial damming of the Neuse River was the most appropriate method of installation for the project. Permitting of the installation required evaluation of the permanent and temporary impacts to the Neuse River caused by the temporary dam and construction equipment. Historical river flows were reviewed to evaluate feasibility of different portable dam methods to provide the force main contractor with options for construction.
The team faced additional challenges associated with the proposed bridge demolition and construction schedule, and associated limitations on construction of the bridge within the Neuse River waters to protect wildlife habitat. Design, permitting, and easement acquisition had to be completed on an expedited schedule to minimize impact to the bridge construction schedule and to adhere to the Neuse River in-water construction moratorium. Close coordination in the planning and design stages between the CORPUD, NCDOT and its design build team, and regulatory agencies was required to successfully execute this project within the desired timeframe.
The project was successfully constructed and placed into operation within the allowable construction timeframe of October 1, 2013 to February 14, 2014.