< Fusible PVC<sup>®</sup> used to Slipline 16” Water Main in Moorhead, MN

Fusible PVC® used to Slipline 16” Water Main in Moorhead, MN

While horizontal directional drilling (HDD) is the most common method for installing Fusible PVC® pipe, sliplining is another trenchless installation method that has increased in popularity over the last several years. Not to be confused with cured-in- place pipe (CIPP) lining, sliplining involves inserting a new, stand-alone pipe into an existing host pipe. The end result is a leak-free, fully-structural pipeline replacement solution that minimizes construction disturbance by utilizing an existing pipeline alignment.

A common concern with sliplining is that the reduction in cross-sectional flow area from the existing pipeline will reduce flow capacity. In actual practice, however, the improved Hazen-Williams Coefficient (C-factor) from using a new plastic pipe, as well as the elimination of tuberculation that may have built-up in the existing pipeline, often results in only minor flow capacity reduction. Additionally, the favorable OD/ID ratio with Fusible PVC® pipe enables end-users to maximize the amount of cross sectional flow area within the existing pipeline.

In Moorhead, Minnesota the local water utility was faced with the need to either rehabilitate or replace an existing 16-inch cast iron water main. The 16-inch main was experiencing failures because bolts holding together the pipeline’s mechanical joints started shearing off due to corrosive soils. Moorhead Public Service (MPS) and its engineer, Apex Engineering Group, decided that trenchless construction utilizing the existing water main alignment would be the least disruptive approach to replace the existing main. Trenchless construction also eliminated the need to design and permit a new pipeline crossing under an existing railroad track.

Pipeline Details and Project Summary
Project/Location: Center Avenue Water Main Replacement Phase 1; Moorhead, MN
Pipe Length/Size:: 3,015 LF 12” DR18 Fusible PVC®Pipe
Installation: Slipline
Owner: Moorhead Public Service
Engineer: Apex Engineering Group
General Contractor: Hough Inc.
Sub-Contractor: KW Boring, Inc.
UGSI Contact: Dan Christensen (715) 206-0518 dchristensen@ugsi.us

Project specifications gave bidding contractors the option to either rehabilitate the existing 16-inch water main with a CIPP liner or slipline a new 12-inch Fusible PVC® pipe inside the existing 16-inch main. Prior to specifying the slipline option, Apex hydraulically modeled the Moorhead system with the 12-inch Fusible PVC® pipe substituted in place of the existing 16-inch cast iron water main. Apex determined that the significant difference in the C-factors between the new replacement pipe and the existing host pipe resulted in only minor changes to pressures and flows within the water model despite the ID reduction.

In response to a request prior to the bid, Apex and MPS also gave bidding contractors the option to directionally drill a new 12-inch water main parallel to the existing 16-inch water main. The low bid contractor, Hough Inc., worked with KW Boring, Inc. and decided to slipline 12-inch Fusible PVC® pipe inside the existing 16-inch water main.

KW Boring used a directional drill rig to pull the new 12-inch pipe into the existing 16-inch water main. A slurry mixture was pumped into the host pipe to provide lubrication during the installation. The absence of bell joints on the Fusible PVC® pipe allowed the new main to be pulled in without casing spacers. After the new pipe was pulled into place, a flowable grout was used to fill the annular space between the new pipe and the existing host pipe.

Kristofer Knutson, water division manager with MPS, was pleased with the end result of the project and commented, “Sliplining with Fusible PVC® pipe was an effective, economical, trenchless solution that allowed Moorhead Public Service to complete the project within a short time frame with minimal impact to customers.”

Layout of Pipe Prior to Insertion

Pipe Insertion into Host Pipe