A Brief History
During the early 1960s, Brooklyn Union Gas Company first pioneered using a compressed air powered lance in conjunction with a vacuum truck as a better way to dig and reduce the costs associated with approximately 30,000 annual street openings for gas distribution pipe repair. Compressed air, or “dry excavation” to dig utility “potholes” proved to be a safe and reliable alternative to manual or mechanical methods of uncovering buried utility lines without damage.
Success with this methodology quickly led to the development of “small hole technology” -- now known as “keyhole technology” -- whereby repairs are made to underground facilities from the roadway surface using long-handled tools. This technology was first reported in the 1960s as utilities sought ways to reduce the size and cost of utility excavations and avoid putting “a man in the hole.” Both Philadelphia Electric (PECO) and Peoples Gas of Chicago were early pioneers in developing keyhole maintenance techniques to reduce the number of large street openings that were both a nuisance to the public and costly to excavate and re-pave.
Early keyholing by PECO included repairs to leaking bell joints and cathodic protection. The pavement was cut with diamond saw blades and removed with pneumatic pavement breakers and concrete drills. A power-driven auger and air jet vacuum removed the spoils, augmented by a clam-shell post hole digger. These techniques seem rudimentary compared with today’s rotary coring and vacuum excavators but resulted in substantial savings to PECO.
Over the next two decades, large dedicated vacuum excavation trucks and rotary coring devices were introduced at Southern California Edison as an alternative to traditional pavement breaking. During this same period, Dravo Corporation of Pittsburgh, PA began the development of a specialized air lance tool for excavation, later named “AirSpade”. Throughout the 1980s and 1990s, AirSpade became widely accepted by other utilities including Baltimore Gas & Electric, and Pennsylvania-American Water.
In addition to uncovering utility lines, dry excavation was tested in several applications during the 1970s and 1980s. This included work with the Department of Defense to uncover landmines and unexploded ordnance, as well as “trenching” for construction. Improvements in equipment included advancements in AirSpade nozzle technology to provide faster excavation.
By the mid-1990s, dry excavation technology also became common within the arboriculture industry, as this same technology was applied to uncover sensitive tree roots without harm. As tree-service companies began to recognize the advantages of this diagnostic tool, many new, low-impact arboricultural applications were developed. Bartlett Tree Experts, the largest US tree-service company, became an early adaptor. At this same time, experiments with high-pressure water led to advancements in hydro excavation.
Typical repairs using dry and hydro excavation came to include cast iron main joint repair, sacrificial anode instillation, low-pressure service cut-offs, new service instillation, and valve box replacements. In addition to utility maintenance, these processes have direct application to other underground operations such as test holes, service drops and shallow slice pits for the telecom industry, daylighting and test holes for directional drilling, and inspection holes for pipeline integrity and Subsurface Utility Engineering (SUE).
Today, countless gas distribution companies and their contractors in North America practice keyhole technology using rotary coring, soft excavation, and core reinstatement. This process achieves average savings of almost $1,000 per repair vs. conventional methodologies. In a recent paper, the Gas Technology Institute reported that over 800,000 utility roadway cuts are made per year. Given the inherent safety and cost advantages, the use of soft excavation for trenching, potholing and keyholing is projected to grow significantly over the foreseeable future.
