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Process of Elimination

Process of Elimination

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    Photo: Hubbell, Roth Clark Inc.

    Western Townships Utilities Authority in southeast Michigan budgeted $600,000 to replace 3000 feet of sanitary sewer that runs along the bottom of a ravine at depths of more than 20 feet. When closed circuit televising revealed open joints, cracks, and groundwater infiltration, the authority decided to restore the 64-year-old interceptor using in-situ lining. Because leakage at the joints and cracked pipe would inhibit curing, they were pressure-grouted before the lining was installed. Total cost: less than $200,000.

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    Photo: Hubbell, Roth Clark Inc.

    Landmark tree-lined streets: A spider web of buried utility lines. The Detroit suburb of Grosse Pointe Farms saved $100,000 while preserving tree roots by replacing 9000 feet of 4- and 6-foot deteriorated cast-iron water main with 8-inch HDPE pipe. Here, workers guide a bursting head into a launch pit. As the old pipe is 'bursted' out of the way, the new pipe is pulled in behind.

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    Photo: Hubbell, Roth Clark Inc.

    At first, it looked like pipe bursting was the ideal way to replace a force main in Ann Arbor, Mich. But a geotechnical analysis showed that soils at the pipe's elevation were loose, and that it was dangerously close to an old, 16-inch water main. That, and because the main had to cross a cemetery entrance as well as an interstate bridge, prompted the city to leave the old pipe alone and lay 3700 feet of 8-inch HDPE at a deeper elevation using horizontal directional drilling. Savings over open-cut construction: $400,000.

To minimize disruption, the public works department wrote a 13-page “Horizontal Directional Drilling Guidelines Handbook” that specifies permitting, design, construction, stormwater pollution prevention, and drilling fluid requirements for contractors working for private utilities in the public right of way. Morehead then taught employees from other departments how to inspect construction sites, and began shutting down uncooperative contractors.

“They got with the program real quick after that,” Morehead says.

Require the project designer to conduct a geotechnical analysis. Soil conditions influence what construction method to use—pipe ramming, for example, works better for loose or unstable soil, such as sand, than in dense material like clay—and bid prices.

Most contract claims on trenchless installations arise from “changed ground conditions.” Owners can minimize potential liability by involving contractors as early as possible in geotechnical investigations.

The extent of the investigation depends on the project-delivery method, says Naresh Koirala, senior technical engineer with Golder Associates in Burnaby, British Columbia, a geotechnical and environmental consulting firm that works worldwide.

For conventional design-bid-build projects, the investigation should be carried out in phases: a preliminary investigation to determine what trenchless construction method would work best given the soil conditions and a more detailed investigation later during design.

With a design-build contract, the owner or its geotechnical adviser conducts only the preliminary investigation because the contractor is responsible for the more detailed investigation. Specialized Services Co., whose clients include Phoenix and Scottsdale, has been retained under design-build and contract-manager-at-risk contracts, not under design-bid-build.

With a “no product /no-pay contract,” the owner doesn't pay if the job isn't installed properly. Of course, owners pay handsomely for offloading all potential liability onto the contractor.

Write a competitive request for proposals. This is easier than you may think, says Jesse Van DeCreek, PE, an associate with underground consulting firm Hubbell, Roth & Clark Inc. in Bloomfield Hills, Mich.

Simply prepare a bid document with all the elements—such as excavation, traffic control, and restoration—of traditional cut-and-cover construction.

Then, assuming you've determined the appropriate trenchless method that will be used, prepare an alternative bid proposal in the same contract that includes all the elements of work unique to trenchless construction for the same length of pipe. In many cases, the per-foot cost to complete the work will be lower for the trenchless method.

For horizontal directional drilling projects, you can also require the contractor to submit a mud-mix design and drill plan that shows how the drill rig and bore path will be set up.

For pipe bursting, microtunneling, and in-situ lining, prequalify contractors or use a quality-based selection process to ensure all elements of the bid—not just price—are satisfactory. Low bid doesn't mean lowest project cost if the contractor isn't capable of the work.

While there's no zero-impact pipe installation method, trenchless construction methods are saving communities millions of dollars on pipe rehabilitation by minimizing disruption.

Related Articles & Links
  • To learn more about products that keep water flowing, click here
  • WEB EXTRAS: To view Overland Park's guidelines for horizontal directional drilling, and to develop specifications for “subsurface utility engineering” services, visit the "Article Links" page.
  • Read the article "Eenie, meenie, miney, or mo?" to learn about four rules of thumb for selecting the right application.