GPR Best Practices | Best Practices for Concrete Contractors Using Ground Penetrating Radar


The construction industry, especially concrete contractors, sits at the intersection of the most technologically advanced job sites and potentially large infrastructure expenditures. As labor shortages remain an ongoing concern for contractors, businesses, and job sites, more are turning to technology to ensure their job sites are safe and unseen hazards are properly identified and reported.

One of the challenges in North America is that developers, contractors and businesses continue to add underground utilities, but rarely remove outdated or no longer used technologies, and there is no baseline. national utility data. The question often arises as to who owns which utility and who can manage which utility.

The global GPR market is expected to grow from $502.4 million in 2022 to $699.9 million by 2026, or over 39%.

Increasingly, building owners, architects, engineers and contractors want imaging to be done to properly identify utilities and structural elements before they start digging. But just knowing that something invisible exists is not enough. Businesses should always find it and verify the location of utilities to comply with security mandates and best practices. Ground Penetrating Radar (GPR) is one of the preferred tools and according to Global Industry Analysts, the Global GPR Market is expected to grow from USD 502.4 Million in 2022 to USD 699.9 Million by 2026, i.e. over 39 %.

Avoid a costly accident

One of the biggest job site hazards is accidentally hitting a utility. There is a utility strike in North America every 10 seconds on average. In 2018, workers reported more than 330,000 underground utility strikes in the United States and more than 11,000 in Canada. These figures represent an increase of approximately 13.5% since 2015.

This is a problem that doesn’t have to exist, and there is a simple solution. By eliminating the threat of accidentally hitting a power line, organizations can save money, not to mention the headaches and risk of loss of life. The industry’s most frequently cited research, a Purdue University study, found that for every dollar spent on utility detection, businesses can save $4.62. Other estimates show that cost savings could be as high as $18 for every dollar spent. The savings can total billions of dollars per year. Shutting down a project due to a utility strike can easily cost businesses at least $2,000 per hour.

There are two main approaches to understanding buried utilities: using a utility detection service or GPR.

Two main technologies help teams detect underground networks:

  • Electromagnetic Locators – Electromagnetic Locators effectively locate metal and metallized utilities, while GPR can help locate other buried objects, including plastic pipes. It is also ideal for locating rebar and post tension cables often found in large buildings.
  • GPR – GPR is the most recognized and valuable tool for investigating objects embedded in concrete structures. Its accuracy and ability to locate items, with little or no disruption, makes it the preferred tool for scanning.

Ground penetrating radar, like the technology seen here with the Leica DSX, can help contractors locate power lines, voids in concrete, rebar, post-tension cables, and more. Many models are available with software to automate data analysis to create a 3D map of the results for easy viewing.Leica Geosystems Inc.

Best Practices for Entrepreneurs

GPR goes do not identify types of rebar. However, it is ideal for looking into a concrete slab, making it indispensable for the country’s ongoing infrastructure initiative.

Before collecting data, contractors should understand what information the customer needs. They also need to know more about the area they are scanning, including the age of the concrete, whether the area will be free of obstructions, and what other safety considerations are needed.

With more crews using GPR, an increasing number of jobsites have multiple GPR contractors on site at the same time. To avoid confusion and ensure that the data collected is usable, teams should agree on a standardized representation of an underground embedment.

It sounds simple enough, but contractors should be familiar with how GPR works, including its limitations. Users should know how and when to calibrate the device and program its parameters to collect the best data based on site specifics.

Crews should also follow industry best practices and generate appropriate markups to minimize confusion on site with other contractors and staff.

  • For example, a pencil or black wood marker is best when marking on exposed concrete if it is not the natural exposed surface. If the black markings are inappropriate or difficult to see, another suitable color – except red – can be used. However, the color should be specifically noted in the pre and post job walkthroughs.
  • Workers should avoid making temporary markings. If necessary – on finished surfaces, such as polished concrete, tiled floors and carpeting, for example – chalk, tape or other suitable devices can be used; contractors should also take photos of the temporary markings.
  • Imaging contractors should mark any embedments interpreted as conduits in red, where applicable. If red is inappropriate, another color can be used and noted on the before and after work tours. However, the color should not be the same as that used to designate the reinforcement in order to avoid confusion.
  • Since GPR cannot initially identify the size or width of an embedding, contractors must mark an exclusion zone at least 1 inch on either side of the center point of an identified embedding.

What does this mean for concrete?

Best Practices for Concrete Contractors Using Ground Penetrating RadarGPR devices can vary in size from large to portable. Depending on the size of the scanning area and the situation, some tasks may be better suited to a walk-behind scanner. Also consider the frequency of the antenna; a low frequency antenna will provide deeper penetration, but targets must be larger to be detected.Leica Geosystems Inc.GPR has no limits for workers and crews who need to locate rebar, power lines and other hidden items. However, it has other limitations, depending on the objective and the depth at which users have to search. The piece of infrastructure will dictate the specific equipment needed for the job. Utility detection radar looks 9 inches or deeper into the ground; a bridge deck is about 18 inches thick, making it ideal for GPR.

GPR goes do not identify types of rebar. However, it is ideal for looking into a concrete slab, making it indispensable for the country’s ongoing infrastructure initiative.

The upper limit for most concrete work is 28”. However, electrical conductivity, aggregate size, air entrainment, water content and admixtures will reduce the depth of GPR effectiveness.

Contractors should define a depth that is at least 50% greater than the planned depth of the objects. For example, the window depth should be at least 15 inches for a 10 inch thick slab.

GPR entered the market decades ago and general awareness has grown over the years. It is becoming more prevalent as prices fall and contractors become less tolerant of accidents and utility strikes. Interpreting the data and positioning it once collected remain important issues for many contractors. The right solution can ease any concerns entrepreneurs may have, and any reluctance to adopt is mostly based on misinformation.

Accidentally hitting a utility is a pure cost to an organization’s bottom line, and the cost of damage increases. Given this, companies should recognize that they are losing money by hitting utilities and embrace technology that can save them time, money and headaches.

Entrepreneurs need to think about their responsibilities, invest in technology and see how profitable they can be. This will save time (and rework), money and lives. If you’re going to be held responsible for utility strikes, why not spend the money and embrace the technology from the start to create “a safe system at work”?

About the Author

Simon Pedley has been involved in the utility detection market for over 16 years, providing technical support, field support and training for much of his career. As a Sensing Solutions Specialist for Leica Geosystems, he is focused on helping surveying, engineering and construction professionals understand and implement technology to achieve damage prevention, security monitoring and mapping of high-value utilities.


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