This group of three emergency contracts negotiated with the City of Portland were to replace severely deteriorated gravity sewer lines that serve the Ross Island Bridge and Naito Parkway interchange and the Lair Hill residential neighborhood of Portland. Utilizing a combination of open-cut, microtunneling and trenchless methods, JWF was able to successfully replace over 4,000 feet of sewer pipeline in an extremely busy section of metropolitan Portland. In addition to the challenges associated with the location, the project also required close coordination with local businesses and residents to minimize impacts and we were able to successfully complete all work with minimum disruption. The open-cut work included construction of 400 lineal feet of 36-inch combined sewer reinforced concrete pipe (RCP), 275 lineal feet of 24-inch diameter cured in place pipe, approximately 1,000 lineal feet of 36-inch RCP at a depth of 15 to 25 feet, and 1,000 lineal feet of 6- to 16-inch sewer services.
Approximately 904 lineal feet of 36-inch reinforced concrete pipe was installed by microtunneling in one drive with two interjacks. The 55-inch diameter microtunnel crossed beneath fifteen traffic lanes serving the greater downtown area, including Interstates 5 and 405, at a depth of up to 45 feet. The conditions which lead to the collapse of the sewer lines also promised challenging tunneling conditions. The emergency nature of this contract resulted in a shared risk approach. The project team collectively decided to eliminate grouting of the dry gravels and cobbles which were encountered at the beginning of the drive. These conditions proved difficult to control at the face of the tunnel machine and the project team agreed to steer it up and out of the gravels and cobbles into more suitable sands and silts. This planned approach to the work resulted in a successful vertical curved drive raising quickly out of the challenging dry gravels and cobbles and into more desirable tunneling conditions. A gyroscope was used for guidance of the machine and surveys were conducted regularly to ensure accuracy of the curve and of the final recovery location.
The remaining portion of the project involved two guided auger bores of 54-inch steel casing with 42-inch HDPE carrier pipe. The first bore was 140 feet which we self performed under a heavily traveled US Highway 26. During the bore, substantial blocks of concrete were encountered, which required removal of the cutter head and auger flights to manually dislodge the concrete. Extreme caution was required to prevent the running soils from creating a void under the road. JWF used a guided auger bore to maintain the precise grade control and alignment required for the gravity sewer to meet design grades and avoid existing underground utilities. A second 300-foot guided auger bore was offered to a minority subcontractor to support the City’s diversity program.
JWF designed and maintained an extensive bypass pumping system that handled abnormally high winter flows, while coordinating closely with the City of Portland Bureau of Environmental Services to identify multiple discharge points. In addition, the project required abandonment of the existing sewer using cellular grout, and the restoration and repair of street surfaces and related utilities in the area of construction.