Keyhole Basics: Coring 101

By E. Marshall Pollock | February 2010 Vol. 65 No. 2
Truck-mounted coring unit with stabilizers

Over the past decade, as utilities and their underground contractors look for more efficient, economical and environmentally friendly ways to make repairs to underground utilities and install buried infrastructure, they are beginning to realize many benefits associated with keyhole technology – the process of making small, surgical circular cuts through the hard surface to gain access to the infrastructure buried below.

Besides a decrease in the need for a large variety of construction equipment on site and the resulting reduction in the environmental footprint when compared to traditional utility cuts, keyhole technology allows for the cored pavement, or “coupon,” to be saved for permanent reinstatement when the underground work is completed which results in substantial savings in permanent pavement repair costs. However, as with many new and emerging technologies, familiarizing new users and helping them to make an informed decision about equipment purchases and proper techniques to carry out these new procedures is critical to success.

Keyhole technology involves a rotary cutting unit, or core drill, that safely and accurately cores an 18-inch or larger diameter hole through asphalt, asphalt-concrete and reinforced concrete road systems, and sidewalks to enable crews to vacuum excavate and view subsurface activity or to repair underground plant from the road surface using long-handled tools. Because the goal is to reinstate the original core back into the pavement after the underground work has been completed, precision and accuracy in the initial coring operation are essential.

There are four key success factors involved in the coring and reinstatement process:

  • Choosing the proper coring equipment;
  • Proper set up and coring procedures;
  • A method of extracting the core; and
  • A bonding compound to reinstate the core back into the pavement.

Choosing the proper coring equipment
Because, at the end of the day, the intention is to put the core back into the road, the coring equipment used to cut it must produce an accurate and precise result. If you are going to throw the core away, any coring unit will probably work.
The selection of the proper coring equipment first depends on the size of core that needs to be cut, is the diameter of the hole needed to perform the underground work and the depth of the pavement.