A Clearer View Beneath the Earth

By: Nicholas M. Zembillas

Thanks to a new technology, locating and identifying underground facilities-especially in large or highly congested areas-has just gotten easier. 3-D underground imaging lets the user see what lies beneath the ground in three dimensions. It creates clear pictures and maps of structures such as buried utility lines, trenches, storage tanks, rock formations and even voids.

3-D underground imaging adds another dimension to subsurface utility engineering (SUE) locating and mapping capabilities. In some situations, especially in areas with few anticipated underground facilities, the more conventional subsurface utility 2-D designating, locating and mapping services are all that is necessary. However, in areas with a known high volume of underground facilities-such as highly urbanized areas with multiple buried utility lines-the heavy congestion may cause 2-D technology to miss some features. This is when 3-D underground imaging excels, because it "sees" in three dimensions, rather than two. It also provides a full, rather than flat, view of what is there.

Unlike conventional ground penetrating radar (GPR), 3-D underground imaging includes 14 radio-wave channels instead of just one. It collects underground data in 5.12-ft-wide swaths, recording in one-in. increments for 100% coverage of the area being investigated. Therefore, 3-D underground imaging is an ideal alternative in larger or wider areas.

In the post-processing phase, special software converts the captured data to standard CAD/GIS format, which can be customized for compatibility with clients’ internal databases. The pictures are so distinct and well defined that it is difficult to believe the facilities can be up to more than 10 ft below ground. In addition, since it works in three-dimensional cubes instead of two-dimensional slices, the 3-D technology is able to locate and map features that may be missed by traditional 2-D technology. Thus, 3-D underground imaging provides a more accurate and comprehensive view of below-ground structures, making it an attractive alternative in areas with a high degree of underground congestion.

The equipment is convenient and easily transportable. The unit itself measures 8-ft wide by 3-ft deep by 2 1/2-ft high. It is pulled by a small all-terrain vehicle and can cover approximately one acre of ground per day.

Due to its 14-channel capability, 3-D underground imaging is much quicker than its 2-D counterpart in identifying below-ground structures, making it potentially more cost-effective when working in larger areas. Its broader coverage enhances the ability to map what is located underground, providing much more information about what lies beneath. For example, on a one-acre site 3-D underground imaging collects 1.6 million radar scans, which takes about one day. Using 2-D technology to collect the same data on a one-acre site would take about four weeks. Furthermore, all of the captured information can be viewed as one picture, providing a comprehensive view.

The increased information that underground imaging provides may make it more cost-effective than other investigative methods. It also may reduce the number of exploratory test holes, or even eliminate the need completely. The imaging is fully GPS-integrated to produce accurate coordinate maps.

"We recently used the technology and our TBE processes at an energy plant that was retrofitting its facility," said John Harter, TBE group vice president, who oversees engineering and operations in the firm's utilities division. "Using 3-D underground imaging, our crew discovered numerous underground utilities and other structures previously unknown that would have remained undetected if we had used only traditional designating procedures and technologies. Rather than risk hitting these underground facilities, the energy company decided on a redesign."

Using 3-D underground imaging can enhance the accuracy of project designs and cost estimates and can streamline the construction phase of any project. It uses all three dimensions to capture the total picture of what is located underground.