When an existing culvert failed causing an entire irrigation canal to wash out, the Harlingen Irrigation District
had to react quickly. They were interested in getting the culvert and canal fixed as quickly as possible so they could maintain the raw water supply to the City of Harlingen Water Works for treatment and distribution to the surrounding community and local farmers supplies. The District needed something that could be installed quickly but would also be a solution they could count on not to fail again.
One of the most critical requirements was to find a product that had the structural capabilities to withstand the seventeen foot height of cover necessary to install the culvert beneath the existing canal. The District concentrated on finding a solution that would not allow water from the canal above to seep into the pipe which could cause infiltration of the backfill and ultimately a washout the entire canal - similar to what they had just experienced with the poorly installed pipe arch culvert.
Even though there were several 9 x 9 and 10 x 10 reinforced concrete boxes (RCB) available from a previous job and were free to the District, Ferris and Flinn, LLC, the project engineer, realized that to make use of this type of solution would involve more time and money then was available. They would also require an entire concrete slab to be poured on top to ensure the structural capacity and prevent the joints from allowing infiltration of the soil below which could result in another washout. Ultimately, they selected a solution supplied by Contech Engineered Solutions which utilized DuroMaxx® Steel Reinforced Polyethylene (SRPE) pipe. Not only is DuroMaxx lightweight, allowing for the use of smaller equipment, but its smaller outer diameter required less trench excavation for a fast installation and its steel reinforced profile could structurally withstand the seventeen foot height of cover.
There were three different diameters installed – 54”, 60” and 72” diameters – each 192 feet in length. While the installation was in progress, the part width construction allowed the District to maintain canal operation while the construction took place. The entire installation took place in two phases due to the bypass of the irrigation canal.
Although several granular backfill materials are perfectly acceptable, the final decision must take into consideration various project circumstances including available trench width and desired speed of installation. In this particular project, a concrete slurry backfill was selected so that no seepage from the earthen canal would find its way into a granular backfill.
It is also important to consider pipe buoyancy to prevent pipe floatation during backfill placement. Contech was involved in grout plan recommendations involving pipe diameter, slurry weight, individual lift thicknesses and other parameters. The critical envelope was backfilled in two days, allowing contractor to begin embankment fill placement.
Frank A Ferris, President of Ferris and Flinn LLC stated, “The primary reasons for selected DuroMaxx SRPE were corrosion resistance, availability and a lightweight pipe which allowed the District to utilize their own equipment. We used varying sizes to reduce the shipping costs.”