As the nation expands in population and evolves in capability, there’s an ever-growing need for new and improved infrastructure. But while enterprises like telecommunications advancement, management of electric, gas and water utilities, construction and roadway development continue to proliferate, land mass stays the same—all while existing frameworks become outdated or deteriorated. As a result, many projects carried out in these industries are burdened by the challenge of working on, in, near or around subsurface infrastructure.
“Existing subsurface utilities and their related structures constitute a significant portion of this infrastructure,” explains the American Society for Civil Engineers (ASCE). “They create risks on projects. Inaccurate, incomplete, and/or out-of-date information on the existence and location of existing subsurface utilities reduces the engineers’, owners’, and contractors’ abilities to make informed decisions and to support risk management decisions regarding the project’s impact on existing utilities.”
That lack of precise information is a hazardous and costly problem. Consider the potential service interruptions for telecommunications companies whose buried lines are compromised by excavation, or the injury risk that can stem from a strike on a natural gas line. Proceeding with project work that does not involve a rigorous utility information and planning stage can have detrimental impacts across a range of industry sectors, which is the very impetus for implementing subsurface utility engineering (SUE).
SUE is the convergence and systematic use of equipment and data-processing technologies that allow for the collection, depiction, and management of existing utility information. It is fundamental to the planning stages of construction and utility work as a means of mitigating the immense risks involved in working with or around buried infrastructure.
The ASCE has outlined a range of utility quality levels in its CI/ASCE 38-02: Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data. Interestingly, the highest of these levels is that which typically relies on the use of hydro excavation. Here’s why.
Breaking Down SUE Quality Levels
The purpose of CI/ASCE 38-02 is to provide project owners, engineers, constructors and utility owners with a system of classifying the quality of data associated with existing subsurface utilities. This classification allows each responsible party to develop strategies for reducing risk by improving the reliability of information on existing subsurface utilities in a defined manner.
A utility quality level is defined as the professional opinion of the quality and reliability of utility information, as determined by the means and methods of the professional. Each of the four existing utility data quality levels is established by different methods of data collection and interpretation. They break down as follows, from lowest to highest:
- Utility quality level D: Information derived from existing records or oral recollections.
- Utility quality level C: Information obtained by surveying and plotting visible above-ground utility features and by using professional judgment in correlating this information to quality level D information.
- Utility quality level B: Information obtained through the application of appropriate surface geophysical methods to determine the existence and approximate horizontal position of subsurface utilities. Quality level B data should be reproducible by surface geophysics at any point of their depiction. This information is surveyed to applicable tolerances defined by the project and reduced onto plan documents.
- Utility quality level A: Precise horizontal and vertical location of utilities obtained by the actual exposure (or verification of previously exposed and surveyed utilities) and subsequent measurement of subsurface utilities, usually at a specific point. Minimally intrusive excavation equipment is typically used to minimize the potential for utility damage. A precise horizontal and vertical location, as well as other utility attributes, is shown on plan documents. Accuracy is typically set to 15-mm vertical and to applicable horizontal survey and mapping accuracy as defined or expected by the project owner.
Quality level A is the most precise of the information levels because it gives visual confirmation of the subsurface utilities residing within the area of the project. The practice of utility daylighting, or potholing, through hydrovac technology has come to be recognized as the safest and most effective method for garnering this visual confirmation.
The Essential Role of Potholing in SUE
36% of annual underground utility damages are the result of excavation issues, with failure to pothole being the largest, and estimated total damages in the U.S. have reached an all-time high, increasing by 16% over a one-year period. There’s an undeniable reason why this approach is considered the highest of quality levels for subsurface engineering work, and that’s because the data accuracy it achieves is unparalleled to any other method. Ultimately, potholing enables engineers, owners and crews to:
- Access critical information and insight. Even armed with charts and utility maps (like those aggregated by the means outlined in quality levels D, C and B), you still run the risk of striking critical underground infrastructure. Having visual verification is as accurate as it gets, and potholing offers distinct insight into the type, horizontal position and depth of buried utility lines, as well as any existing damage to them.
- Prevent worker hazards. Data shows that construction crews face digging-related deaths and injuries every year. Without a reliable way to locate and bypass crucial underground utility infrastructure, the wellbeing of excavation operators is seriously endangered. Potholing enables teams to locate dangerous infrastructure so as to prevent these hazards.
- Prioritize efficiency. While potholing may feel like an extra step in the project process, it can actually save time in the long run. It minimizes the possibility of mistakenly hitting a line and causing the kind of damage that renders significant downtime and precipitates unforeseen extensions to the project timeline. Potholing is also a much faster method of identification than relying on charts and maps.
- Keep costs down and maintain compliance. In addition to the high expense of project downtime, there’s also the massive cost to repair vital utility lines ranging from water, electrical and gas to telecommunications and fiber optic. Because projects that fail to pothole have increased potential for wrecking excavation equipment or incurring noncompliance fines, this aspect of SUE is vital to staying on budget and in sync with regulatory bodies.
Hydrovac for Potholing in SUE
The potholing method involves digging a series of very small test holes, usually measuring approximately 6 to 12 inches deep, into the ground to accurately identify subsurface pipes, lines and other obstructions. As you can see in the description for quality level A, this should involve “minimally intrusive excavation equipment … to minimize the potential for utility damage.” That’s why this practice often leverages a hydrovac approach and equipment to obtain the necessary verification of underground objects all along the project’s bore path.
The process of hydro excavation is implemented for this process via the application of highly pressurized streams of water to soften the ground soil and displace it from the potholing bores through high-suction vacuum equipment. The benefit of this excavation technique is its ability to move hard or rocky ground without accidentally puncturing or harming the features below.
Of course, any highly effective process of hydro excavation relies both on the people doing the work and the actual trucks and equipment. That’s why Merut Construction prides itself on maintaining a skilled, experienced crew and a fleet of hydrovac trucks that highlight the importance of doing each job well and safely. In the end, effective subsurface utility engineering requires the kind of hydrovac effort that meets high standards.
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