Launch Slideshow

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Utility microsurgery

Utility microsurgery

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    Coring the street in a residential area is done quickly and easily by a two-man crew.

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    The advantages of small keyhole cuts are readily apparent in these two utility cuts, which cause large, unsightly scars in the street.

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    The core from a utility cut is set aside. It will eventually be replaced and fused into place with a bonding material.

Small-hole or keyhole technology in the utility maintenance industry is the equivalent of microsurgery in the healthcare industry. Those who embrace this innovation are achieving benefits and cost-savings for themselves, their stakeholders, and the municipalities where they operate.

The fundamental approach consists of opening the street surface using pavement coring technology, performing repair tasks through the 18-inch diameter cored hole with specialized extension tools, and reinstating the core removed in the first step via a specifically formulated bonding material. This low-intrusion approach to performing routine repairs and infrastructure upgrades is packed with benefits for customers, the work-force, and the community.

Although the technology requires investments in capital equipment, specialized tooling, and retraining workers, the benefits for all of the stakeholders can provide substantial returns on those investments. A street coring machine, which costs from $30,000 to $90,000, saws an 18-inch diameter core or plug from the street surface. The earth over the top of the infrastructure is removed using a vacuum excavator, which typically costs from $60,000 to $80,000, resulting in a vertical tunnel directly down to the area of infrastructure to be repaired.

Workers, standing on the street surface and not inside of an excavation pit, “operate” on the infrastructure using specialized extension tools. Most first-time implementers initially invest about $20,000 to $35,000 in tooling to perform an average of three to four repair types. When the operation is complete, the earth is replaced and the street plug that had been set aside is reinstated using a specifically formulated bonding agent. The “healed” street surface is as strong as the original surface and the “scarring” is minimal.

Depending on how the street coring and vacuum excavation components are configured on the truck chassis, the fleet investment can run from $50,000 to $100,000. Some first-time investors invest in training and consulting services to shorten the startup time and begin gaining returns on the technology quickly. Those who use these services estimate spending around $30,000 for the advice and training.

Why should a public works department consider using keyhole technology? Because like microsurgery, smaller and less intrusive is better. If one makes the analogy that cutting a road is like cutting one's skin, then a smaller hole means a shorter recovery time and a less intrusive operation. Keyhole technology has been used primarily by the natural gas industry, but this technology has the potential to be used used on drinking water pipelines and by government agencies for subsurface utility engineering on urban reconstruction projects.

Keyhole cut history

The roots of small-hole work can be traced to the mid-1960s. Philadelphia Electric Co. and the Institute of Gas Technology co-authored a paper, “Repair of Bell and Spigot Joints Through Small Openings,” which was presented at the Leak Control Symposium in August 1963. This study examined the repair of cast iron joints using encapsulation methods through small-hole excavation using vacuum technology. For the next two decades, this process evolved with mostly specialized contract forces locating and repairing multiple joints, day-lighting the entire joint, and using workers dipping head-first into the small hole to install a boot entirely around the joint.

In the 1990s, anaerobic sealants emerged on the scene. This repair operation consisted of drilling a small hole in the top of the joint and injecting a sealant to revitalize the joint material. This created a major milestone in the infrastructure surgery process, allowing the pipe to be repaired entirely from above the hole. The development of above-ground tools made the scope endless. Now the gas industry is not only making cast iron joint repairs, but working together with Des Plaines, Ill.-based Gas Technology Institute (GTI) to undertake steel main repairs, curb valve installations, anode and test station installations, new and replacement service installations, service cut-offs, plastic service cap repairs, and underground utility verification.

The long-term goal is that whatever can be done today in a 3x4-foot excavation can be accomplished through a small hole. Paramount to this is the increased development of sophisticated locating tools.

PECO Energy Co. (PECO), formerly Philadelphia Electric Co., helped develop small-hole work in the 1960s. The company's path followed that of the gas industry, with primarily cast iron work done in small holes with vacuum excavation. But in the mid-1990s, the vacuum truck helped provide great cost savings in the field of pre-engineering work. It was from this that a full-time underground utility verification team was formed that helped develop precision locating tools.