Using GPR to Locate Utilities
GPR has many uses, for surveying, planning, archaeology, and for preparing a work site. Using GPR to locate utilities is one of the primary functions of Ground Penetrating Radar. It is a simple and effective way of finding pipes and cables without having to dig up roads, pavement or driveways.
How GPR Works
Using GPR to locate utilities is surprisingly simple. GPR relies on radio-waves which are sent into the ground, and bounce back to be picked up by receivers in the radar device. The length of time it takes the waves to come back gives an indication of the density of the material under the ground and where it is. GPR is not completely perfect, but it is quite accurate and useful for detecting voids, pipes and dense objects. For this reason, it is often used by the military, geologists, archaeologists, builders, and planners.
How GPR Can Find Utilities
Finding buried pipes can be tricky. Sometimes, if the pipes are metal, builders will energize the metal pipes with electric currents, and then make use of a magnetic field sensor to pick up that current. Unfortunately, not all pipes are made of metal, and it is easy for the flow of electrical current to be disrupted if there is a break in the pipe or if the join of the piping is made from a non-conductive material.
GPR offers a good alternative since it can pick up on not just metallic objects but also non-metallic objects, and it can also detect voids in the pipe, as well as buried structures and disturbed soil. It will give an indication of where the pipes are and how deep they are likely to be.
GPR waves will be absorbed by clay or by saline, and this means that there are limits to the type of ground you can work with as well as how deep the utilities can be buried before it becomes ineffective.
For this reason, many technicians will work with multiple types of tool. Where GPR is employed, it can either be operated manually, with the technician marking potential utilities or other anomalies as they are found or by creating larger subsurface maps and ‘depth slices’. The latter method is the best one to use in complex and difficult ground because it creates a broader image which means that there is more tolerance for error.
Locate and mark is useful if the ground is favorable and the subsurface is generally uncluttered because any reading is simply ready to be investigated. Where more anomalies are expected, it makes more sense to plot a full map so that the readings can be compared against each other. The end result is a map which can be used to inform plans to dig up an area, ensuring that utilities do not get damaged in the process.
GPR is particularly helpful in older towns and cities where plans are not available, or where utilities may have been extended or modified without proper permissions being obtained from the local authority.