When Size Matters: CCCP Solution For Large Inverted Siphons Rehab

By Angus W. Stocking, L.S. | June 2011 Vol. 66 No. 6

The Sabine River Authority (SRA) of Texas was created in 1949 to equitably distribute the waters of the Sabine River and its tributaries. As part of this distribution, “We provide surface water to eleven industrial customers, such as Conoco and Louisiana Pigment, for cooling and processing,” says SRA Facility Manager Mike Carr.

This water is conveyed mostly via a 35-mile long open canal. But where that canal must cross under roadways and railroad tracks, the water passes through inverted siphons.

The siphons are made from reinforced concrete pipe that is typically used in storm sewers and other low pressure applications. But the siphons are usually full and, with wear and movement over time, leaks and structural cracks have occurred.

“Most of this concrete pipe went in back in the ’70s,” explains Carr, “and now we’re seeing broken lips at the joints, a lot of leakage, and sediment is getting into the water and compromising quality. Also, the possibility of collapse at the crossings is a danger to the public and the railways. When we see problems, we have to fix them.”

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The Authority is systematically rehabilitating all 40 siphon crossings in its network. The preferred method is cured in place pipe (CIPP) and SRA has a long history with this method. But CIPP hasn’t worked well in large diameter pipe for the SRA.

Two crossings in particular were problematic. One was a roadway crossing with three 84-inch diameter siphons running parallel for 180 feet. The other was a railroad crossing with two 78-inch siphons running parallel for 185 feet. Both were bid for CIPP.

“We’ve used linings before with a lot of success, but that was mainly on pipes up to 42-inches,” explains Carr. “We tried to use cured linings on pipe this size and ran into problems.”

Bad experience
In fact, the first attempt at cured-in-place lining one of the 78-inch siphons was a disaster as the lining collapsed and had to be cut out and removed. A second attempt was successful, but not totally satisfactory. There was visible sagging at siphon ends, and the Authority was uneasy about structural integrity. Carr asked the project engineer, Meyer & Associates, to look into alternatives. The contractor, Boh Brothers Construction Company, also wanted an alternative for the larger diameter siphons, and suggested CentriPipe, a centrifugally cast lining solution used by one of their associated firms, Repipe-Texas. CentriPipe turned out to be a successful alternative for these troublesome large-diameter crossings.

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