Survey-grade locators are those whose accuracy and reporting support ASCE quality level B and above. Although “survey-grade” is a misnomer, because the highest level of utility locating for survey use is QL-A, which requires daylighting or potholing to actually see what’s buried underground, professional private utility locators like GPRS can support the efforts of subsurface utility engineers (SUE) and surveyors, offering a high degree of precision in locating and mapping underground utilities.
This use of NDT (Non-destructive testing) technologies like ground penetrating radar and electromagnetic location are essential for preventing utility strikes and ensuring the safety and efficiency of construction and excavation projects. Understanding the intricacies of so-called survey-grade locators involves delving into the realm of SUE, NDT, RTK positioning technology, and the potential hazards associated with underground utility strikes.
Subsurface Utility Engineering & Surveying
Subsurface utility engineering (SUE) is a branch of civil engineering that focuses on the identification, mapping, and management of underground utilities. It integrates geophysics, civil engineering, and surveying to create a comprehensive understanding of subsurface conditions. SUE is critical in the planning and execution of construction projects, particularly in urban areas where the density of underground utilities can be remarkably high.
Surveying within the context of SUE involves detailed measurements and mapping of underground infrastructure such as water pipes, gas lines, electrical cables, and telecommunications networks. Traditional surveying methods often fall short when dealing with underground utilities, necessitating advanced technologies to achieve the required accuracy and reliability. This is where survey grade locators come into play.
What is a Survey Grade Locator?
The American Society of Civil Engineers (ASCE) has established the Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data. Their guidelines outline various methods for obtaining utility location data and categorizes these methods by different quality levels. These quality levels indicate the reliability of the locate data: the higher the quality level, the more accurate and dependable the data. This allows project planners to make more informed decisions, thereby reducing the risk of utility strikes during excavation.
The quality levels (QL) assigned to each variety of underground utility assessment provide surveyors and engineers with a guide to understand the accuracy of the utility locating information they seek. The quality levels are: D, C, B, and A. Only QL-B and QL-A contain the accuracy needed to qualify for SUE. GPRS does not conduct SUE, however our non-destructive underground utility methods have a 99.8% accuracy rate and can support QL-B SUE efforts.
As mentioned earlier, “survey-grade” for any utility locating that doesn’t involve potholing is a misnomer, but the proper use of NDT technologies that allow for a high level of accuracy allow utility locators to detect and map the precise location of underground utilities without digging. Unlike standard locators, which may provide approximate locations, those locators whose methods support SUE level QL-B offer high precision and accuracy, typically within a few centimeters when paired with the use of Real-Time Kinetic positioning. This level of precision is essential for tasks that require exact measurements, such as designing infrastructure, conducting risk assessments, and preventing damage during excavation.
RTK Positioning Technology
Real-Time Kinematic (RTK) positioning technology has fast become a cornerstone of modern surveying. RTK is a satellite navigation technique used to enhance the precision of position data derived from satellite-based positioning systems such as GPS (Global Positioning System). While standard GPS can provide location accuracy within a few meters, RTK technology refines this accuracy to within a few centimeters.
RTK works by using a fixed base station and a mobile receiver. The base station remains in a known, fixed position and transmits correction signals to the mobile receiver. These corrections account for various errors, including satellite orbit errors, atmospheric interference, and clock discrepancies. As a result, the mobile receiver can determine its position with much greater accuracy.
In the context of utility locators, RTK technology allows for precise mapping of underground utilities. By integrating RTK with electromagnetic or ground-penetrating radar (GPR) technologies, survey grade locators can detect and map utilities with a high degree of accuracy. This integration ensures that the position data of underground utilities is both reliable and precise, facilitating safer and more efficient construction practices.
The Dangers of Underground Utility Strikes
Underground utility strikes occur when construction or excavation activities inadvertently damage underground utilities. These incidents can have severe consequences, including:
- Safety Hazards: Damaging gas lines, electrical cables, or water mains can pose significant safety risks. Gas leaks can lead to explosions, while severed electrical cables can cause electrocution or fires.
- Service Disruptions: Utility strikes can disrupt essential services, affecting households, businesses, and public infrastructure. This can lead to significant economic losses and inconvenience.
- Legal, Financial, and Reputational Consequences: Utility strikes often result in costly repairs and potential legal liabilities for the responsible parties. Regulatory bodies may impose fines, and affected utility companies may seek compensation for damages. And when there are significant accidents or injuries from a utility strike, it makes the news and can irreparably damage your reputation.
- Project Delays: Striking an underground utility can halt construction projects, leading to delays and increased costs. Ensuring accurate utility location is crucial to maintaining project timelines and budgets.
Preventing Utility Strikes with Accurate Survey & Engineering Support
The precision of survey grade locators is instrumental in preventing underground utility strikes. By providing accurate location data, these devices help construction and excavation teams avoid damaging underground infrastructure. The process typically involves several steps:
- Planning and Research: Before any excavation begins, a thorough review of existing utility records is conducted. This historical data provides an initial understanding of where utilities might be located.
- On-Site Detection: Survey grade locators are used on-site to detect and map the exact location of underground utilities. Technologies such as RTK, GPR, and electromagnetic detection are employed to ensure accuracy.
- Mapping and Documentation: The detected utilities are mapped and documented, creating a detailed subsurface utility map. This map guides construction activities, ensuring that excavation is performed safely.
- Ongoing Monitoring: Throughout the construction process, continuous monitoring and re-evaluation of the subsurface conditions are necessary. This ensures that any changes or new findings are accounted for, further reducing the risk of utility strikes.
Private utility locators who support QL-B are vital tools in subsurface utility engineering and surveying. Their ability to provide precise and accurate location data for underground utilities helps prevent utility strikes, ensuring the safety, efficiency, and cost-effectiveness of construction and excavation projects. By leveraging advanced technologies such as RTK positioning, these locators play a crucial role in modern infrastructure development and maintenance.
GPRS maintains a 99.8% accuracy rate on over 500,000 jobs and counting thanks to the outstanding education and training of our Project Managers. Every GPRS Project Manager must undergo rigorous training to achieve Subsurface Investigation Methodology (SIM) 101 certification before they work in the field. SIM allows customers to know that whether you hire GPRS near you, or require regional or national utility locating services, your Project Manager will provide that same standard of care and clarity of reporting to help keep your job on time, on budget, and safe.
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Frequently Asked Questions
What is potholing/daylighting in construction?
Potholing, also referred to as daylighting, is when an excavator digs under the surface of a site to physically see and assess utility lines. Potholing, just like any kind of ground disturbance, requires a contractor to call for an 811/One Call utility locate before digging, which can be cumbersome to a schedule. And, if you don’t have an easy-to-follow ground disturbance policy for excavation, that includes locating all public and private utilities, even with a solid 811 locate of public utilities, a utility strike can easily happen because 65% of all on-site utilities are private, not public.
What is the average cost of a utility strike?
According to research conducted for GPRS by Finch Brands in 2021, the average cost of a utility strike to a facility (college campus, manufacturing plant, hospital, etc.) is $56,000, plus 6-8 weeks of downtime. Learn how GPRS can map your entire subsurface infrastructure to help you avoid costly and dangerous utility strikes, here.
How many underground utilities are struck in the U.S. on average?
According to information from the Common Ground Alliance (CGA), there is an underground utility strike every 45-60 second in the United States. Most of those strikes are caused by incomplete, inaccurate, or misunderstood utility locating information. Learn how you can control the quality of your infrastructure information, here.
