When a 17 mile long Phoenix, AZ, water main was originally installed in 1975, the pipeline from its treatment plant traversed largely undeveloped land, but the city’s significant growth over the past 33 years has brought residential and commercial development adjacent to and directly above the waterline easement.
When a condition assessment of the existing prestressed concrete cylinder pipe (PCCP) using electromagnetic and forensic analysis identified the need to completely rehabilitate the pipeline, innovative construction techniques were used to achieve dual objectives: employ the least possible intrusive methods while providing a long-term, rehabilitated product, keeping time and cost factors in mind.
Currently, general contractor Kiewit Western is on track to rehabilitate 18,000 feet of “priority number one” (areas of critical rehabilitation need) using split can sliplining pipe.
Nine access pits
In order to gain access to the buried existing pipe, nine large excavations called portals were constructed, spaced between Tempe and Mesa. Due to extremely poor soil conditions along the Salt River and aforementioned city developments, the deep pits were shored using the slide rail method of soil support. Roughly 35,550-square-feet of slide rail were used. Three portals were 54-feet-long, 24-feet-wide and 23-feet-deep; three were 50-feet-long, 34-feet-wide and 29-feet deep; and the three largest were 90-feet-long, 25-feet-wide and 24-feet deep.
Slide rail system
The slide rail system for the 90-foot-long portal was manufactured by PRO-TEC Equipment, Charlotte, MI, and supplied by local shoring specialists Trench Shore Rentals, headquartered in Scottsdale. In addition to using 8-feet by 20-feet (4-inches thick) and 8-feet by 16-feet (4-inches thick) panels, 55-foot external Walers, braced to spreader and corner posts, were used to provide clear span accessibility. PRO-TEC’s Railing Post System, a guard rail device that enhanced the safety factor of job site personnel, was installed around the perimeter of the excavation.
Split can liners
Split can liners consist of steel plate rolled to the required diameter but not longitudinally welded. They are banded to a diameter about 10-inches less than the host pipe diameter. The existing PCCP pipe ranges from 72 to 96 inches in diameter. Slipliners are installed through the portals, spaced approximately 2,500 to 3,000 feet apart. Typically, two pipe sections are removed at each portal and steel liners are installed in each direction from the pit.
A cradle was installed between the PCCP sections at each portal. The liners were placed on the cradle and transported to the correct position within the host PCCP pipe. Once in place, the bands were cut from the steel liners and tack welded. After several liners had been fitted into place, the liners were welded longitudinally and circumferentially. The annular space between the finished line and host PCCP pipe is then grouted.
The overall project was started in 2005 and is targeted for final completion in 2013.
FOR MORE INFORMATION
PRO-TEC Equipment, (800) 292-1225, www.pro-tecequipment.com
Kiewit Western; (303)979-9330, www.kiewit.com