By Jim Johnson

Assignment Use a Grundocrack with special adapter to burst cast iron water main beneath busy three-lane highway.

-Grand Junction, Colorado
The thought of trenching through busy downtown streets was not favorable for Trent Prall, Utility Engineer for the City of Grand Junction. Yet, the city needed to upsize an old 6 inch cast iron water main which ran under two heavily trafficked thoroughfares to accommodate increased water needs.

Excavating the 70 year-old main also presented another concern. Colorado Department of Transportation required that all open cuts through state highways be backfilled with a lean mixture of sand and Portland cement. Not only was the special fill expensive, the city would need to pay for the transport of the spoils. Seeing the dollar signs starting to stack-up, Prall investigated other installation options.

Through various trade journals, Prall had become aware of pipe bursting. "When this application came up, we looked at (pipe bursting) in more detail during the design phase. Then we decided to make it an option for bid," stated Prall.

What Price Trenching?
The water main replacement was divided by Prall into two installations. In each case, the lowest bids were from bursting contractors. In fact, bursting came in at an average of 17 percent lower than open-cut.

M.A. Concrete Construction (Grand Junction, CO) provided the low bid for the second burst. M.A. Concrete Project Manager Jeff Nimon had two concerns with the project: maintaining water service and bursting through numerous stainless steel repair clamps.

A Nose for Bursting
Both bursts were performed with a pneumatic Grundocrack pipe bursting system. M.A. Concrete used a Grundocrack Hercules bursting tool, manufactured by TT Technologies, Inc. of Aurora, IL. To handle the stainless steel repair clamps, Nimon had a secret weapon ... known in the trade by the slang name of "schnoz."

The schnoz is a patented tool produced by TT Technologies for difficult bursts. Placed ahead of the tool during a burst, it concentrates force to penetrate difficult materials.

"The schnoz allows our tool to be incredibly productive where other trenchless tools fear to tread," remarked Dave Holcomb, TT Technologies Vice-President and Regional Sales Manager.

Providing Temporary Water
Before M.A. Concrete could shut down the main and start their 500 foot burst, they needed to provide a temporary supply of water. By connecting a line to a fire hydrant, crews bypassed the main and continued providing water to the neighborhood.

Puttin' Down the Hammer
With the main bypassed and their bursting equipment in-place, it was show time. The Hercules got off to a good start, splitting and bursting the old cast iron pipe and stainless steel clamps. Upon encountering each clamp, the tool slowed or stopped completely. However, the hammer action of the pneumatic tool continued to exert force to penetrate the vast majority of clamps.

As the tool traveled, it also pulled-in high density polyethylene replacement pipe. Prall selected 8-inch diameter SDR 13.5 PE pipe because its extra thick skin would not be affected by remnant cast iron shards. Once the burst was completed, the new PE pipe was connected at each gate and normal service was re-established.

Above ground, crews used a pipe fusing machine to butt-fuse lengths together. Electrofusion couplings and service fittings were used underground for tees and hydrant connections. M.A. Concrete crews also used electrofusion service saddles, which eliminated the need to put a fusion machine in the entry pit.

Successful Conclusion
Prall expressed that pipe bursting not only saved tax money, but also saved taxing the community's patience by eliminating disruptive open cutting and restoration. Said Prall, "In the future, we'll include pipe bursting anytime we're bidding a full replacement job."