We have been in the preconstruction phase of a brownfield project for about 18 months. In the process, we have been using a relatively new and still evolving set of technology tools, called ground penetrating radar (GPR). This geophysical method uses radar pulses to image the subsurface.
Knowing what is underground is particularly important for the job I mentioned. This 25-acre site was originally a manufacturing plant dating back to 1910. It had many honeycombed shafts, mines, equipment foundations, utilities and who knows what else. Over the years, the density of commercial development surrounding the site had made it desirable for commercial. The problem: No one knew the extent of these existing conditions. That’s where GPR came into the equation.
With GPR, a device is rolled over the area of interest. Data is reported by 2-dimension printout or 3-dimensional model. Data is then read to decipher the changes in the density of the materials and thereby pinpoint the material type and conditions below the surface. Normal depths for accuracy depend upon the type of material. In our case we were going down about 45 feet.
We’ve seen a few benefits of using GPR:
- It beats concrete x-raying. That method required access to both sides of the slab to get a good reading, so only elevated slabs where a fit.
- It’s not destructive. Electromagnetic radiation detects the reflected signals from subsurface structures.
- It works on a variety of media. Rock, soil, ice, fresh water, pavements and structures are candidates.
- It’s versatile. GPR can detect objects, changes in material and voids and cracks.
We think GPR will become more important as our population and areas of development become more dense. Have you used GPR with success?