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Keyhole Standards and Approvals

1. The first formal Construction Standard for Keyhole Coring and Reinstatement was introduced in Toronto, Canada, where the keyhole coring and reinstatement process itself was developed in the late 1990’s by Consumers Gas (now Enbridge Gas Distribution) and promulgated by the City of Toronto in November 2007. TS 4.70 City of Toronto: Construction Specifications for Keyhole Cores and Permanent Core Restoration.


2. The second formal Construction Standard for Keyhole Coring and Reinstatement was introduced in Montgomery County in August 2009 as Specifications for Utility Construction Permit.



3. The third formal Construction Standard was developed by the municipalities around Phoenix (Maricopa Association of Governments – MAG) and was promulgated in August 2010. 



4. The forth formal Construction Standard was developed by the municipalities around Las Vegas (Clark County and The Regional Transportation Commission of Southern Nevada) in November 2010 and came into effect on January 1, 2011.




5. Each iteration was patterned on the previous ones and variations are discussed in the Annotated Version. 










Construction Standards for Keyhole Coring and Reinstatement - Overview

NEW (January 2014) Rules and Regulations for Construction in Chicago in the Right of Way recognize and approve Keyhole Coring and Reinstatement

In January 2014, Section 4.1.10 of the Rules and Regulations for Construction in the Public Way of the City of Chicago, specifically recognizes and approves keyhole coring and reinstatement for subsurface utility investigation or facility leak detection or repair in city streets. In doing so, the Regulation exempts keyhole coring that follows the guidelines from the more rigorous and complex conventional pavement restoration requirements that include full pavement restoration from curb to centreline or to the nearest horizontal or tranvesrse joint, milling and overlay with hot mix asphalt and full perimeter sealing.


The coring guidelines specify that the pavement core shall not exceed 18 inches in diameter and shall have a center hole drilled through the pavement so that it can be lifted out and replaced in its entirety when work is complete. The soft material shall be removed using vacuum excavation as required. Upon completion of utility work, suitable salvaged backfill material (or appropriate replacement aggregate or flowable fill) and new sand shall be placed back in the hole and compacted in one foot lifts using a tamping rod up to about one inch below the core bottom. The final inch of backfill shall be replaced with pea gravel. The hole shall be filled with a bonding compound, Utilibond or equivalent material. Then the pavement core shall be leveled in place leaving a smooth paved surface. After the bonding compound sets, the surrounding pavement shall be cleaned of all debris and excess grout. Grout material to be used must be Utilibond or other similar grout material approved by the Commissioner. The keyhole technology means and methods shall permit normal vehicular traffic to resume over the restored keyhole location within 30 to 45 minutes of the completed repair.

Reference pages 4-7 from Standards



Washington Gas (WGL) partnered with the Gas Technology Institute (GTI) and major keyhole vendors to promote and utilize keyhole technology techniques for use in the greater Washington, D.C. area across several paving jurisdictions. The primary focus of the project was to advance the current state-of-the-art small-hole technology within Washington Gas with a focus on gaining jurisdictional approval through presentations and field demonstrations. Keyhole technologies have been successfully employed by utilities for many years to reduce excavation and restoration costs. However, gaining jurisdictional acceptance of paving core reinsertion is relatively new.




The project focus incorporated the complete process integration of street coring, vacuum excavation, O&M work through small holes, and pavement core restoration. The project utilized existing keyhole methods, tools, procedures, and products to achieve a successful program startup. To insure success, WGL used experienced contractors and service providers known in the keyhole industry. This paper outlines the steps Washington Gas took to both start up its keyhole program and the steps necessary to secure jurisdictional approvals for pavement core reinsertion.






  • To update Council on two amendments to ROW management ordinance approved November and December 2003

  • To recommend revisions and to explain implementation guidelines

  • To provide an update on cut permit and enforcement activity

  • To inform Council about the Utilicor method of hard surface repair

City of Dallas - Keyhole Coring and Core Restoration

Keyspan (National Grid) and Con Edison win approval for Keyhole Coring and Reinstatement from New York City DOT.



Facilitated by GTI (Gas Technology Institute) and under the direction of Gerry Lundquist, George Mirtsopoulos and Cosmo Iannicco, crews from Keyspan Energy Delivery (now National Grid) and Utilicor Technologies performed demonstrations of the keyhole coring and reinstatement process, on an abandoned gas service cut-off, for the New York City Department of Transport on March 9th, 2006. The process gained quick approval from the DOT.


In addition to the Utilicor coring equipment and Utilibond, the demonstration included the Excavac vacuum excavation system, service cut-off tools from various manufacturers and the soil compaction supervisor from MBW.

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