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Slipline Construction Accelerates Hibbing’s Pipe Replacement Schedule

Hibbing Public Utilities’ water supply transmission mains developed several major leaks from external corrosion which led to the design of pipe replacement. HPU chose trenchless construction to replace the failing water mains and limit construction impacts to the community. In less than one year, three trenchless projects were completed to restore sound, reliable water supply to Hibbing by sliplining a new pipe within the existing pipeline.

Trenchless Project 1 – Fall 2024
Water main replacement for a 24-inch ductile iron pipe located along US Highway 169 was required and multiple construction methods were evaluated. Sliplining of a new smaller water main through the existing pipe was determined to be the preferred installation method. Sliplining would provide a new water main pipe with limited disruption to the traveling public, adjacent utilities, existing pavement, and storm water channels. Additionally, sliplining was estimated to be a lower cost option than several other construction methods. 

The project was designed with approximately 1,350 LF of 18-inch Fusible PVC pipe to be sliplined into the 24-inch pipe. Fusible PVC pipe provides a restrained joint pipe with no gasketed connections within the trenchless alignment. The project was competitively bid in July 2024 with Minger Construction of Jordan, MN the low bidder. Construction commenced in September 2024 and was completed within one month.

Waterworks distributor Core & Main supplied pipe fusion, creating a single 18-inch pipe of 1,350 LF length. Minger Construction installed the new Fusible PVC pipe by pulling the pipe forward into the open end of the existing pipe with their excavator. The excavator pulled the pipe forward with a nylon strap, while moving parallel to the pipe alignment north of the insertion point, then the excavator moved back north and began pulling again. 

With all connections completed, the open access points were bulkheaded, excavations back filled, pressure testing completed, and bacteria tested passed. For grouting the annular space between the new and old pipes, 2-inch piping was installed through the bulkheads and brought to the surface. Once all testing was completed and the pipe was operational, the annular space was grouted with cellular concrete. 

Trenchless Project 2 – Spring 2025
A one mile stretch of HPU’s 30-inch water main supplying the City was anticipated to be replaced or rehabilitated later in the 5-year capital improvement plan. With cost and schedule savings from the 2024 project, the work was moved up and bid in December 2024. The 30-inch cast iron water main was installed in 1967 and has experienced several leaks due to exterior corrosion. The project was competitively bid and Geislinger & Sons of Watkins, MN was awarded the work. Bids for the project were significantly less than the budgeted amount, providing costs savings for HPU.

Pipe fusion was completed by Core & Main in March 2025 with three separate slipline segments planned. In this project, 5,220 LF of 18-inch Fusible PVC pipe was sliplined through the existing pipe. The slipline installations began the first week of April 2025. Despite significant weather delays, the project was completed in less than two months from start to finish.  

This slipline installation was completed using a directional drill rig to pull the pipe through the existing 30-inch pipe. Subcontractor EBI Drilling of Duluth, MN completed the slipline installation with their Vermeer D100x140 rig. Based on water main valve locations and site conditions, three slipline segments were completed. The two longest segments were approximately 2,100 LF. Installing the new pipe with a directional drill rig provided consistent installation force and speed, monitoring of pull forces, and overall quick installation rates. Pull forces averaged less than 30,000 lbs. throughout installation. 

Trenchless Project 3 – Summer 2025
During completion of the second project, additional failures on another section of the existing 30-inch cast iron main occurred. This led HPU to complete an emergency project to slipline another 4,905 LF of the pipe. This water main was not expected to be replaced until late in their 10-year schedule.  Geislinger and Sons completed this slipline project as well. Underground Solutions supplied pipe and fusion services starting in July 2025. 

This section included approximately 2,400 LF of water main under the local golf course. EBI Drilling returned with their directional drill rig to complete two slipline segments on this portion. The longest segment between an existing valve and bend fitting was over 3,200 LF. Installation of this segment saw pull forces averaging around 25,000 – 30,000 lbs. The highest pull force, less than 50,000 lbs., occurred to restart the installation after sliplining was paused to allow additional pipe fusion. Due to recurring large rain events this summer, extremely wet and muddy conditions prevented the entire pipe length from being laid out ahead of installation. Therefore, during the slipline installation, two segments were fused together to create a single pipe over 3,200 LF. The project was wrapped up in mid-August.

Conclusion
Overall, greater than 12,000 LF of important water supply pipes were rehabilitated through sliplining. Through these three trenchless construction projects, Hibbing Public Utilities achieved significant cost savings over other installation methods, which allowed key transmission main replacements to occur years ahead of schedule.