Sliplining & HDPE Provide Fix for Colorado Irrigation Tunnel

In 1901, a key irrigation tunnel was hand dug into the Western Colorado landscape to provide water from the Gunnison River to local farmers. One-hundred and ten years later, that tunnel suffered a collapse when layers of shale fell and blocked irrigation services to 94 percent of the North Delta Irrigation Co.’s (NDIC) headgates.

The tunnel, classified as an earthen ditch by the Colorado Water Conservation Board, travels through shale mountainsides and mesas as it winds through the Rocky Mountains east of Delta, Colorado. Today, 2,300 acres of land are irrigated by the tunnel’s water. A total of 174 shareholders depend on the water each year to grow crops that range from corn to beans to alfalfa.

Choosing and Executing a Method
Following the 2011 collapse in the irrigation tunnel under the Cory Bench, a solution was sought. At first, completely new alternatives were explored. The NDIC considered different delivery methods of their water rights, including pumping water out of the Gunnison River, boring a new tunnel, lining the tunnel with steel liner, using concrete box tunnel construction, and sliplining with high-density polyethylene (HDPE) pipe.

According to evaluation criteria documents available through the State of Colorado, “pumping and boring a new tunnel were eliminated as choices, as the cost of pumping would be prohibitive, and the cost of boring a new tunnel would be prohibitive.” The NDIC also lacked an easement for boring. The steel lining system was comparable in price to HDPE, but was eliminated because of the shorter service life. The concrete box tunnel was scrapped because of a concern in the stability. In the end, the NDIC turned to 1,500 ft of 54-in. SDR 17 HDPE pipe to reline the tunnel. By rehabilitating the tunnel, the NDIC could reopen the full 23 miles of irrigation line to shareholders. With funding from the Colorado Water Conservation Board and the Gunnison Basin Round Table, work began in April 2012.

Petty Construction Company LLC, was chosen for the project. Petty Construction has two locations, in nearby Grand Junction, Colo., and Dickinson, N.D. The firm was no stranger to working with HDPE pipe, with plenty of experience of fusing pipe from 1-in. in diameter and larger.

After sliplining was chosen as the method to pursue, contractors on site used a unique method of dispersing a concrete grout backfill.

The full range of the company’s ability was on hand as they fused the 1,500 ft of 54-in. pipe, as well as a bunch of 2-in. diameter pipe lengths that stretched to 200 to 300 ft long. The 2-in. pipe lengths were used to push the grout backfill into the hole as the pull occurred.

To create the unique concrete grouting method, Petty fused the lengths of 2-in. pipe near the construction of the large 54-in. pipe. Once a group of smaller diameter lengths was completed, workers strapped the pipe lengths to the top and sides of the larger pipe.

The pull of pipe was thought to be relatively simple, as the grade for the tunnel was relatively flat for the first half of the tunnel with a slight downhill grade for the rest.

Tom Petty, managing member of Petty Construction, stated in bid document communications available through the State of Colorado that “we propose to utilize our directional bore machine to bore through the cave in. We will use a back reamer to wash and drag out the spoils from the tunnel on the Highway 65 side of the tunnel. We will use water from the open irrigation ditch to help carry the spoils out of the pipe to be inserted. The HDPE will be carried down the existing service road, and fused together in the open ditch and pulled into the tunnel using our directional drill.”

A Variety of Fusions
The grout pipelines were joined with a McElroy Pit Bull 14, which is capable of fusing butt fusing pipes from 1-in. IPS to 4-in. DIPS (32- to 110-mm). The machine’s compact size and light weight allowed workers to carry the Pit Bull along the 50-ft sticks of pipe that had been laid out along the ground.

Both the 54-in. main pipe and the smaller 2-in. pipelines were joined with butt fusion. The process has been a popular method for creating leak-free pipelines for more than 40 years. The process starts by “facing” or shaving the pipe ends simultaneously so that the ends can be joined together with heat to create a continuous, sealed pipeline. The welding of the pipes is accomplished by using a hot plate or heater that comes in contact with the faced pipe ends. This heats the pipe to a molten state. After the heater’s removal, the pipe ends are pressed together under a controlled force to form a weld that is as strong as or stronger than the pipe itself.

To join the large 54-in. SDR 17 pipe, Petty Construction contacted McElroy distributor High Country Fusion to rent a Certified McElroy Rental MegaMc 2065. The 2065 butt fuses pipe from 20 to 65-in. OD (500- to 1,600-mm). The machine accommodated the 54-in. pipe due to the installation of inserts in the jaws of the fusion machine. Inserts reduce the circumference of the jaws to match the diameter of the pipe. This helps hold and reround the pipe for a better, more accurate fusion process.

Petty Construction chose a Certified McElroy Rental fusion machine because they are held to a higher standard than other rental fusion units in the marketplace. A Certified McElroy Rental location, like High Country Fusion’s, must check fusion machines using a McElroy factory-created checklist. If parts are needed, only genuine McElroy parts are used. Consistent training and audits ensure that each location maintains high-quality rentals.

Above all of the operations, the pipe was staged on top of Cory Bench. A piece of heavy machinery would bring a 50-ft stick of 54-in. pipe down one at a time and place it within the jaws of the MegaMc 2065 and within the built-in pipe roller of a MegaMc Pipe Stand. The pipe stand offered a self-contained, gasoline-powered HPU that could move the pipe up to 24 in. laterally and 34 in. vertically. This flexibility allowed fusion technicians from High Country to easily line up the pipe ends for the fusion process.

The pipe stand provided the largest benefit when heavy machinery was used elsewhere. The stand allowed the machinery to work and not “babysit” the pipe as it was being fused. The stands also prevent damage to the fusion machine.

The fusion area wasn’t as long as the tunnel itself, so after an initial length of pipe was fused, the pipe was pulled through the tunnel and a new 50-ft stick was fused onto the new tunnel liner. This process was repeated until the pipeline was complete.

The North Delta Irrigation Co. was happy with the timeline, cost and installation process using HDPE. Officials from NDIC believe HDPE could have a future in their irrigation system as they identify and pursue new projects within their 23 mile system.

Tyler Henning is public relations specialist at McElroy Mfg.