Surface Penetrating Radar

I think they're now less than $10k. Thirty years ago (middle 1970s) they were well over $100K. Works well when there's little to no clay and/or moisture in the soil.

I priced a system last year made by a company in New Hampshire. The complete package was going to be around $16K.

Have not utilized GPR for many years, has it improved much? I remember we had trouble defining utilities below 10', and it took a trained eye to interpret. Someone with the skills an ultrasound tech. Would like to try again.

Our area is nearly all clay soils. Guess we can forget using it here.

When I lived in NE, I penetrated the clay soils every day.....

with stakes....;-)

Works well enough for things you don't want to dig up, like unexploded munitions.

I wouldn't design from it though......

Generally not the highest level of accuracy or precision.

I just finished working on a project where I called in a GPR guy to scan a foundation slab that was allegedly failing. I stood there all day watching him do the work, and when I saw what the GPR was outputting I was disappointed in the complexity involved in reading the information. It was not nearly as clear and intuitive as the advertisements are, and in many cases you can't tell what you are looking at. This is true even for the operator doing my project, and also for the interpreter who prepared the report. It also did not give exact depth to the rebars because it has to be calibrated against something of known depth.

I challenged some of the readings in the report even though the firm is very reputable and has been doing that type of work since GPR was available commercially.

It ain't what the ads make it look like.