When areas were excavated, workers were exposed to potential hazards of damaging pipelines or hitting live wires under the surface — understanding how Geomapping works can make excavation of lines much easier. (Read Why a Detailed Geotechnical Report Means Success for Your Trenchless Project.)
What is Geomapping
Geomappng is a method of locating underground utilities. Workers use a variety of technological equipment, including GPS and EML to distinguish underground lines from other objects. The resulting information is presented view which includes the subsurface objects along with the surrounding area including any buildings, mountains, rivers, roads, pipelines and estuaries. (Read The Geotechnical Investigation: Which Method Should We Use?)
What Equipment is used for Geomapping
Technological advancements have made it easier to update maps. Tools such as electromagnetic locators (EML and ground-penetrating radar (GPR) help technicians find the subterranean utilities.
Electromagnetic locators work by tracking the electromagnetic field generated by the alternating current traveling along a cable. The oscillation of current gives off a frequency, measured in Hertz. The frequency and electromagnetic field are detectable using a cable locator.
There are two main ways that EML wands work, passive and active modes. Passive mode detects the naturally occurring electromagnetic field generated from the AC traveling along the cable. However, this mode only detects a live cable, like streetlights when they are on. If there is no power flow through the cable during the sweep, the lines are not detected.
To locate all underground power lines, workers may use the wand with a signal transmitter. The signal transmitter is a small portable unit which induces the signal through a cable or pipe which may not have current running through it. By inducing a signal through the line, the cable locator can detect the utility.
Ground Penetrating Radar
Ground-penetrating radar (GPR) transmits an electromagnetic pulse into the ground. The onboard sensors measure the time elapsed between transmission and reception of the reflected signal. Using the known propagation speed of sound through ground, workers can determine the depth of the object from the soil surface. (Read The View Underground: Ground Penetrating Radar.)
All GPS devices have multiple antennas which allow emission of different radar signals. High-frequency signals offer high resolution but limit the depth of investigation. Lower frequency signals increase the depth of investigation but lower the resolution.
During data collection, workers can review the information onsite, often in real-time. Once data acquisition is complete, the sections are analyzed using specialized software. During the post-processing analysis, the software can generate models to get a graphical representation. The analysis helps to reveal features under the soil surface along with an image of the surroundings above the soil’s surface.
Benefits of Geomapping
Underground utilities can be difficult to maintain at the best of times. When lines are originally laid, workers map their location so they can be maintained. However, as new utilities go into an area and old conduits removed or replaced, maps do not always get updated.
Lack of accurate mapping makes it difficult for utility workers to do their jobs when it comes time to repair or replace damaged pipelines. It makes it trying when construction may damage subterranean lines if they are not properly marked. Marking lines during extreme weather such as snow or heavy rain may mean the loss of the physical markers such as paint or flags.
Using the ground-penetrating radar to visualize the underground as it occurs. Most machines allow the user to track multiple projects on screen so the worker can see where multiple lines cross for better understanding of the utility layout. Depending on the sensor, the worker may get a forecast of what may occur based on the collected information.
Public works departments use Geomapping to help locate underground lines as a way of planning for repairs and rehabilitation of existing lines. It also helps them plan new projects after accurately gaining a current map based on the readings of existing subterranean lines.
Once GPS data is imported in a database, other public works departments can use the information to locate underground lines that may need repair or replacement. By having data readily available to other staff allows government entities to save money when developing prints and reports.
Workers can access a central digital database without dozens of paper reports printed, copied, and distributed. As workers can update the database as needed, the most accurate information is available at the touch of a button.
Creating Accurate Maps
The data collected using GPS is useful in generating real-time maps. In a recent study conducted by Muhammad Bilal, et al., data were taken during the Mapping the Underworld (MTU) initiative in the United Kingdom helped to create updated utility maps. Workers collected data for this project using a multi-sensor mobile laboratory which deployed multiple sensors across different locations. The sensors detected various types of buried infrastructure.
Researchers used the data collected from the multi-sensor mobile laboratory to create Bayesian data fusion models, which were used in the Bayesian mapping models. The Bayesian mapping models use automation techniques for segmentation recognition, classification, and hypotheses extraction and connections associated with manholes. From this information, workers can design accurate maps.
Problems with Mapping Underground Utilities
Geomapping underground utilities are not without its setbacks. For example, GPR devices are useful in locating objects below the surface, without the hassle of digging up the objects. However, there are drawbacks in using this technology. These machines require an expert, typically trained in geophysics, to interpret the results.
And the machines are also designed to operate at a walking pace. Workers who may walk too fast or too slow may distort the results, making it impossible to get an accurate map. Some soils, such as clay and aggregate, make it difficult to get accurate readings from GPR systems.
Locating old pipelines shouldn’t be guesswork. Through ever-advancing technology, Geomapping is making easier for workers to accurately locate underground utility lines. The best methods include a variety of tools to map the area.