Keyhole Technology:

More than 50 years ago, entertainer Eddie Cantor reminded us that itsometimes takes 20 years or more to become an “overnight success.” That may alsoapply to new technology as well.

Small hole technology — or what is now called keyhole technology — seeks tomake repairs to underground plant from the road surface using long-handledtools. This technology was first reported in the United States in the early1960s when utilities looked for ways to reduce the size and cost of utility cutexcavations and avoid having to “put a man in the hole.” Both the PhiladelphiaElectric Co. (PECO) and Peoples Gas Light and Coke of Chicago were earlypioneers in developing a number of small hole maintenance techniques in aneffort to reduce the number of large street openings that were both a nuisanceto the public and costly to excavate and repave.

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According to a report presented to the Institute of Gas Technology in August1963 by W.E. Rosengarten Jr., early keyhole repairs undertaken by PECO includedrepairs to leaking bell joints and cathodic protection through a narrow“keyhole-like” slot 4 in. wide and 18 in. long.

“The area to be excavated is laid out on the pavement with a piece of 2 by 4.On concrete highways, this rectangle is cut with a diamond saw. The penetrationof the highway is made using standard pavement breakers and concrete drills. Theremoval of the dirt can be accomplished easily using a power driven auger toloosen the dirt and an air jet vacuum cleaner removes the spoil. A clamshellpost-hole digger is also a very useful tool. The hole is belled out slightly atthe bottom to permit some room to maneuver around the pipe.”

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Although by comparison to today’s rotary coring and vacuum excavationtechniques, the early procedure seems a little rudimentary but it appears tohave achieved the desired results.

“[The keyhole process] resulted in very substantial savings for thePhiladelphia Electric Company. The excavation of this small hole can be easilyaccomplished with simple tools and the small volume of dirt removed, usuallyless than 2 cubic feet, is very easy to handle. The worksite is confined to asmall area reducing the interference with traffic.”

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In the next two decades, large, dedicated vacuum excavation units supplantedthe “vacuum cleaners” and the clamshell post-hole diggers and typical small holesizes increased to 2 ft by 2 ft to accommodate more repair applications. Duringthis period, rotary coring of small-diameter holes using portable coring deviceswas introduced at Southern California Gas as an alternative to traditionalpavement breaking methods.

But it was not until the early 1990s, when the Consumers Gas Co. of Toronto(now Enbridge Gas Distribution) experimented with reinstating an 18-in. diametercore back into the pavement after the repair had been completed. Soon, the majorsavings potential of the keyhole process was realized. Instead of disposing ofthe core as spoil, Enbridge developed a bonding compound that allowed them toeffectively reinstate the core in the pavement as a permanent repair — requiringno temporary patching or repaving. This resulted in huge savings in time andmoney.

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Golder Associates, the international engineering firm that provided theengineering proof of the process for Enbridge and monitored performance over a10-year period from 1992 to 2002, reported that they cored and reinstated morethan 3,000 utility cut repairs in streets and sidewalks in Toronto with nofailures. Regular monitoring of high traffic sites showed no weakening ordegradation of the reinstated cores or adjacent road system, even thoughmillions of commercial and other vehicles had passed directly over the keyhole.

As a result, Golder concluded that “the equipment, procedures and materials,including Utilibond, developed and used by Enbridge over the last 10 years, willensure satisfactory long-term performance of pavement reinstatement.”

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This type of long-term research has gone a long way in helping to convinceskeptical municipalities and other road authorities that the coring andreinstatement process, when properly executed, is effective in minimizing damageto pavement and the underlying roadbed.

“Nothing succeeds like success,” says Buddy Secor, manager of engineeringtechnical support at Washington Gas, which implemented the coring andreinstatement program in 2004. “The Golder 10-year study was instrumental inhelping us gain approval for the process from more than a dozen municipalauthorities in our service area.”

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Today, more than 20 local gas distribution companies and their contractors inNorth America employ rotary coring and reinstatement in their keyhole activitiesand are achieving average savings of almost $1,000 per hole over conventionalmethods of pavement cutting and rehabilitation.

Typical utility repairs through keyholes include cast iron main joint repair,sacrificial anode installation, low-pressure service cut-offs, new serviceinstallation and valve box replacements. In addition to utility maintenance, theprocess also has direct application to other underground and trenchlessoperations including: test holes; service drops and shallow splice pits for thetelecommunications industry; daylighting and test holes for directionaldrilling; and inspection holes for pipeline integrity and SUE.

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The Gas Technology Institute estimates that in 2004 more than 800,000 smallholes were cut through pavement in North America, but only a fraction — lessthan 2 percent — employed this innovative process.

Some of this delay in acceptance is due to resistance encountered at themunicipal level where those who own the right of way are reluctant to move awayfrom traditional repair methodologies. Improperly restored utility cuts can anddo affect pavement performance and contribute to deterioration and reducedpavement life. We need no more proof of that than an examination of our roadsfollowing the fiber-optic boom of a few years ago.

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But things are changing there too. Independent studies, such as thesoon-to-be-released “Restoration of Utility Cuts Study” conducted by theNational Research Council of Canada and the U.S Army Corps of Engineers,document the superiority of keyhole excavation and reinstatement overconventional methods and recommend utilization of the keyhole process wheneverfeasible.

“The credibility of that study, which involved a number of North Americancities, utility companies and U.S. state departments of transportation, shouldgo a long way in dispelling some of the myths or ‘conventional wisdom’ thatsurround the restoration of utility cuts, and replace them with facts,” saysColin Donoahue, vice president of field operations at Utilicor Technologies, themanufacturer and distributor of the pavement coring units and bonding materialdeveloped by Enbridge.

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Utilization of keyhole technology will also grow as more and more utilities,under pressure to reduce costs and improve operational efficiency, look for newprocedures and methodologies to reduce construction and maintenance costs. Thesecosts represent at least 60 percent of their operational budget, and thepotential of multi-million dollar savings that can be realized through keyholetechnologies has reached the level of utility boardrooms.

Obviously, keyhole technology cannot accommodate every kind of repair andopen trenching and other more intrusive methods will be around for a long time.But utilities and their contractors continue to make a strong case at themunicipal level for new, less intrusive procedures, including directionaldrilling and pavement coring and reinstatement.

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At the same time, more and more municipalities are beginning to recognize thesignificant advantages that coring and reinstatement can offer their citizens.The absence of jack-hammers and pavement breakers makes for less disruption ofthe neighborhood and the replacement of conventional, low-strength cement groutswith super-fast strength gain bonding agents, like Utilibond, means that theroad can be safely reopened to traffic within 30 minutes of the completedrepair. This results in less traffic disruption, shorter road closings, lessstructural damage to the road system, longer pavement life and reducedmaintenance, resulting in huge tax savings for local ratepayers.

The keyhole coring and reinstatement process is also a winner from anenvironmental standpoint. There is no road cut spoil to be disposed, notemporary patching compounds with volatile organic compounds to escape into theatmosphere and the significantly smaller circular keyhole footprint meansreduced scarring of the community landscape.

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These were the key factors that persuaded the Dallas-Fort Worth Metroplex toformally approve the keyhole coring and reinstatement process and to exemptAtmos Energy TXU from having to employ pavement slurry techniques in therehabilitation of the roadway after completing keyhole repairs.

“This was a huge step forward for us,” says Marc Chapman, Atmos Energymanager of repair and construction in the Dallas-Fort Worth area. “As cities inTexas continue to upgrade their paving requirements to include flowable fill,slurry sealing entire blocks of streets, panel-to-panel concrete replacement andcolor matching of existing pavement, we need to work with them in adopting newtechnologies that will ease this burden on the utility and at the same time meetthe needs of the municipality in maintaining its infrastructure.

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“For us at Atmos, coring technology is certainly the way of the future andwill continue to be one of our main tools in minimizing paving expense andimproving relations with municipalities.”

In Toronto, where the coring and reinstatement process was born 15 years ago,city officials have approved it as a permanent repair. Councilor Jane Pitfield,head of the works committee, says the process “leaves the road in bettercondition than it was when they cut into it.” She is seeking to apply theprocess to other city-owned utilities like the water system.

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That kind of recognition at the political level may be what is needed to kickstart the process in other municipalities. Pothole-conscious politicians arebeginning to recognize that taxpayers also benefit from the reduced impact thatthis type of pavement “microsurgery” has on the road itself and from the longerroad-life and better pavement performance that results. This recognition at themunicipal level bodes well for the future expansion of keyhole technology.

After 40 years, Eddie Cantor may have been right — keyhole technology hasbecome an overnight success.

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