Phoenix Water Main Undergoing Innovative Methods

Wed November 18, 2009 - West Edition
CEG

Split can steel liners are banded to a diameter 10 in. (25.4 cm) smaller than the host PCCP pipe to allow easy installation.
Split can steel liners are banded to a diameter 10 in. (25.4 cm) smaller than the host PCCP pipe to allow easy installation.



When the 17-mi. (27 km) long Phoenix 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.

So 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 least possible intrusive methods while providing a long term rehabbed finished product, keeping time and cost factors in mind.

Currently, general contractor Kiewit Western is on track to rehabilitate 18,000 ft. (5,500 m) of Priority 1 area (areas of critical rehab 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 shoring method of soil support. Roughly 35,550 sq. ft. (3,300 sq m) of slide rail were used, sourcing from three manufacturers. Three portals were 54 ft. (16 m) long, 24 ft. (7.3 m) wide, and 23 ft. (7 m) deep; three were 50 ft. (15 m) long, 34 ft. (10 m) wide, and 29 ft. (8.8 m) deep; and the three largest were 90 ft. (27 m) long, 25 ft. (7.6 m) wide, and 24 ft. (7.3 m) deep.

Slide Rail System

Slide Rail for the 90 ft. long portal was manufactured by PRO-TEC Equipment, Charlotte, Mich., and supplied by local shoring specialists Trench Shore Rentals, which is headquartered in Scottsdale and has branches in Phoenix and Tucson. In addition to 8 by 20 ft. (2.4 by 6 m) by 4 in. (10 cm) thick and 8 by 16 ft. (2.4 by 4.8 m) by 4 in. thick panels used, 55 ft. (16 m) 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 in. (25 cm) less than the host pipe diameter. The existing PCCP pipe ranges from 72 to 96 in. (182 to 243 cm) in diameter.

Slipliners are installed through the portals, spaced approximately 2,500 to 3,000 ft. (762 to 914 m) 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.