Technical Training Manual
Operationally Superior Keyhole Coring Equipment from Utilicor
Not all coring equipment is created equal
Basic coring equipment commonly used to cut circular holes through concrete or other hard or paved surfaces has
been designed to cut the hole with no thought to the possible reuse of the cored coupon in the cost-effective restoration of the material – in our case the roadway – from which it was extracted. These basic coring or drilling machines are a mechanical hole saw driven by a small gasoline engine or electric motor, with a manual feed system held in place by the operator, or mounted on a portable stand secured to the surface of the material to be cut by its own weight or the combined weight of the operator, or temporarily anchored to the pavement by screw-in lugs or a rudimentary vacuum system. These basic devices are not very expensive, not very accurate, not very fast, and sometimes, not very safe – but they will cut a hole.
However, where the core diameter is large (12”, 18” or 24”), or the material to be cut is thick (8” to 18” or more), or the core or coupon that is removed is to be replaced in cost-effectively restoring the paved surface -- as in a keyhole project -- a much more stable and robust piece of coring equipment capable of accurate and finite adjustment should be used to safely and accurately cut the core.
With this in mind, all Utilicor coring units are manufactured to achieve the three fundamentals of a successful keyhole core cutting program: a stable and robust coring platform; a coring mechanism that is fully adjustable in both the horizontal and vertical planes to ensure that every core is cut perpendicular and true, or plumb, with the horizon and not the road surface; and a means - the center pilot hole - to safely extract the core or coupon cut from the roadway, and to safely and accurately manipulate it during the reinstatement process.
Because springs are integral to most wheeled vehicles, it is important that the suspension of the truck or trailer on which the unit is mounted, be isolated during the coring process. Otherwise, much of the downward pressure or vertical force required to initiate and sustain the coring action will be lost or absorbed by the suspension causing poor or erratic cutting action.
This problem can be solved by utilizing hydraulic stabilizers fixed to the deck or frame of the vehicle, on either side of the core drill. When deployed, these stabilizers take the spring action out of the suspension and concentrate the weight of the vehicle down through the core drum for an accurate and precise cut. The stabilizers can also be individually adjusted to accurately orient the core drill so that it is perpendicular to the horizon in the plane that parallels the width of road.
Utilizing the stabilizers as described above, together with the capacity to tilt the coring mast in the vertical plane, all Utilicor equipment can be properly adjusted to compensate for both the transverse camber or slope of the roadway, as well as its longitudinal angle or grade. Proper orientation of the core drum perpendicular to the horizon is essential to cutting a core that can be properly reinstated.
When the coring drum is set up perpendicular to the horizon, NOT the road surface, the effect of gravity on the core is eliminated which reduces the chance of the core getting stuck inside the coring drum. Proper orientation of the core cutting process will also ensure that the sides of the hole are plumb so that gravity will not interfere with the uniform flow of the bonding compound around the reinstated core, or cause the material to pool on one side or the other, resulting in a potential void during reinstatement.
An important feature, central to all Utilicor coring equipment, is the unique center pilot bit that simultaneously cuts a 2 3/8” pilot hole through the center of the core while the circumference of the core is being cut by the drum. The pilot bit not only centers and stabilizes the cutting process, but the pilot hole that is created allows for the insertion of a special core puller tool that extends through all the layers right to the bottom of the core, which is important should the layers of pavement come apart or delaminate. When adjusted, the rubber stopper on the core puller tool expands, friction-tight, inside the pilot hole, allowing the core to be easily and safely removed from the roadway and when the work is complete, reinstated back into the roadway.
Without a center pilot hole, cut simultaneously or drilled separately, the only way to get the core out is with some form of clamping device or surface-based extraction method such as sinking lag-bolted into the core. Not only is this another time consuming step, but it will not work if the pavement layers have delaminated, or on hot days, when the asphalt is soft and there is a real danger in the lag bolts pulling free, causing damage or injury to the operator.
Finally, there is the issue of core-weight. A typical 18” diameter core 10” deep weighs 215 lbs. Using a pry bar through the eye of the core puller, two men can share the load and lift the core. A 24-inch diameter core of the same depth weighs 380 lbs. and requires a hoist or crane to lift. All truck and trailer mounted Utilicor coring units come with an optional core hoist to assist crews in safely extracting and replacing heavy cores.
Truck mounted stabilizers are crucial for isolating the suspension and creating a solid platform to core from
Coring perpendicular to the horizon allows for proper core extraction and reinstatement
Without a center pilot hole drilled all the way through the core, core extraction is problematic and proper core reinstatement becomes impossible