The right solution

Dec. 18, 2015

In May 2015, the city of Ithaca, N.Y., contacted Don LeBlanc of the Snap-Tite Culvert Liner team (a division of ISCO Industries) to discuss and review a failing culvert underneath a major road in town. The culvert liner team specializes in analysis and the rehabilitation of structures via segmental lining.

Town engineer Dan Thaete met with LeBlanc on the jobsite to discuss possible lining solutions.  The host culvert was approximately 110 ft long and consisted of a 7-ft by 7-ft concrete box culvert on the upstream end and a 7-ft diam. rail-car metal pipe on the downstream end. At the transition between the materials, there was a deflection which made a lining solution even more challenging.

The structural component of this culvert required H25 loading and approximately 24 ft of soil cover. The watershed was estimated to produce approximately 780 cu ft per second during the 100-year storm event. In the design model, the culvert was determined to be in inlet control, a hydraulic condition in which the pipe capacity is limited by the area of the opening and its geometry. By considering a smooth inner wall pipe with a Manning roughness coefficient of 0.012 or better and a bevel on the inlet of the culvert, the pipe liner was approved as the proper solution. The beveling of the inlet allowed for an entrance loss coefficient (k) of 0.2.

The town decided to utilize the DuroMaxx Steel Reinforced Polyethylene (SRPE) pipe option, a product manufactured by Contech Engineered Solutions, as the suggested material. The pipe has a smooth HDPE interior and a low-profile thickness made from HDPE and steel. The complete HDPE encasement not only allows for improved flow characteristics, but also has improved resistance to abrasion and pH variations in soil and/or water. The pipe is also lightweight, which makes it easier for the contractor to handle. The 72-in. inner diameter pipe only weighs approximately 65 lb/ft.

The selected contractor was CLH & Son from Auburn, Maine. CLH had to be strategic with how it approached getting the liner pipe in position as access was limited on the upstream side, making it difficult to get any construction equipment close enough to the opening of the culvert. A crane was utilized to lower the pipe and then each piece was winched into position. The host pipe was prepared with 2-in. by 4-in. pressure-treated wood, which was subsequently lubricated to allow the pipe to ride on a smooth surface. The pipe joints were extrusion-welded with internal bands that spanned each conjoining pipe. Bulkheads were built and grout, consisting of cement, water and an admixture providing a density of approximately 40-50 lb/CF, was applied. The entire lining and grouting process took about 6 days from start to finish.

In conclusion, the city of Ithaca was able to avoid a large excavation—estimated at approximately 30 ft deep—and avoid digging up an active roadway by utilizing a segmental lining solution. 

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