Having the ability to locate and map utilities is an important thing for any contractor that does a lot of major works outdoors. Using GPR for utility locating is a handy and non-invasive option.
GRP works by sending out radar signals into the ground, and then tracking how long it takes for the signals to ‘bounce back’. This is a safe and non-invasive option that allows for utility pipes and wires to be identified before you start digging.
Options for Finding Utilities
GPR is just one option for finding utilities. Other options include energizing metal pipes or cables and then using a magnetic field sensor to find the current. This can be a good way of finding utilities that are nearby, however, it will only work if the target is reachable for connection and if enough current is able to flow through it. In addition, the detector used must be sensitive enough to find the current. In ‘ideal’ circumstances it is cost-effective and efficient. However, there are many scenarios where it will not work.
GPR for utility locating is a good option because it is more flexible and can be used in a wider range of circumstances. It has its own limitations. GPR does not work well in water-rich environments, for example. However, in urban environments, it can be very effective. The trick is knowing when it should be applied and having an understanding of the surrounding area so that the system can be calibrated properly.
Using GPR In Urban Environments
The most common way of using GPR to find utilities is to locate and mark as you move across the site. Another option is to map the whole area and create depth slices. If you are mapping a complex area then the latter option is usually more effective. Locate and Mark works very well for flat open spaces such as parking lots and roads, however, since you can simply look for the area that you know the drain or pipe is likely to be in and scan that one area, moving the GPR back and forth and marking out the anomalies on the scan.
More complex mapping may be needed in areas where you want to be sure that you have 100% coverage. Mapping is an option, but it will require that a lot of radar pulses are sent out at clearly marked out intervals. This kind of GPR still remains a much more cost-effective option for locating utilities than it would be to start digging and hoping for the best!
To get the best results, GPR systems usually operate on the 100MHz to 500MHz ranges, especially for sensors deployed on a cart for mobility. The best thing about this kind of set up is that once you arrive at the site you can start using the system immediately, and have results within minutes for smaller scans, since the display unit allows you to view the results as you go, while saving the results for more detailed review at a later date.