Locating Inside Utilities

[FreedMan]

I know I saw a thread some time back here on the vine where the subject of locating interior wiring and/or under floor utilities came up, but I'm damned if I can find it now.

I've got a couple jobs coming up next week doing just that and I want as to get as many opinions, tips, and tricks as I can before I walk into the swamp. I've done this sort of locate a time or two in the past, but it's been years and all I really remember is the feeling of wanting to slit my wrists by the time it was over.

I've got several frequencies to choose from and lots of extra long jumpers and grounding tricks up my sleeve, but am I leaving anything out or missing some other obvious trick? GPR is not an option.

[ifinditunderground]

It's no different than locating in any other place with terrible congestion of utilities. Take your time, direct connect or clamp everything you can find, use low frequencies, and run ramdom sweeps in every direction you can run them with each and every hookup. You'll know when you are marking rebar and/or wire mesh in the floor. Investigate it thoroughly, and then ignore it once you are satisfied that you can eliminate that interference from underslab, or inslab utilities. Grounding outside of the building may or not work for you, but then again, it might. I always grounded within the building, but keep a loooong jumper with you so you can ground where you need to. Be creative and patient and don't forget to look behind every door, and in every nook and cranny you can find that will tell you where the utilities come up thru the floor. And, Good Luck.

[GWJ_CAS]

Why is GPR "not an option?
We do interior locates quite frequently at places like hospitals, labs, universities etc...sometimes the only way to definitively answer the question is with GPR, especially in those facilities with PVC, PE, HDPE or fiberglass ducts buried within the slabs. Many times our clients are performing some type of floor cut or penetration and missing things like radiant floor heating, gas tubing for the Bunsen Burners in the lab or the PVC sanitary line in the slab are hyper-critical and GPR is the only way for nearly all of these things.

Aside from in-slab utilities, we often deal with post-tensioned slab sections, where mistaking a post-tensioing cable for a rebar can be catostrophic. There is no way to discern the difference with an EM device, ferro-magnetic system (James R meter) or anything else for that matter short of GPR.

If you have the potential for any of these types of installations and GPR is not in your arsenal...make sure you get an iron-clad hold harmless / liability waiver or walk away...

I was called to work for an insurance investigation group as a subject matter expert and expert witness in a case where a locating firm performed an interior locate, without the benefit of GPR, and a group of three post-tension cables for a floor span were cut in the ensuing construction. The building suffered a minor "structural event" and required several hundreds of thousands of dollars in repairs. The contractor sued the locate firm for negligence. The firm's insurer refused to cover the claim once it was revealed that GPR was not used as the firm claimed it did not have access to a GPR system. When it was learned that GPR systems are a readily available and commonly used and are also easily rented, the insurer declined to cover the incident as the firm was determined to be negligent in its practices and contracted for work without exercising due care to protect itself and its insurer from unnecessary liability exposure.

Hope this helps...

[ifinditunderground]

CAS, you are right on the money, I didn't even get into that stuff since we don't locate post tensioned cables withn floor slabs. I always direct that work to an experienced concrete scanning company.

[Mke]

I agree with Gregg, However, I have to state that depending on the locate the GPR may or maynot be cost effective.

Freed didn't really give us too much information on what type of inside locating he is doing. He may or may not be familiar with Post-tensioning cables, grade beams, radiant heat, or any other of the thousands of things you can find in any given building. I tend ot always refer out to GPR companies when it comes to the tensioning cables. Those can be catestrophic when missed.

I have also had the oppertunity to follow a local GPR company and have found things that they were not able to pick up, but they were able to find things I wasn't able to pick up. With that being said, an inside locate is similar to any other locate. There is things you can find, and things you can't. the only difference is you are going to be limited in mobility, unless it is a big box store and you have room to roam.

The best thing I can advise to you Freed, is to hook up to anything you can find... Receptacles, sinks, drains, visable conduits and the like. Make sure you get access to the equipment rooms, depending on the building there should be a Fire supression room, Electrical room, comm room, boiler room and any other room the building maintanence guys can think of. Sometimes there maybe even more than one. Mark accordingly. Don't use paint unless its ok, If its Carpet I use Tape, if it is linoleum I use keel. If your not sure how to hook up to things try anything. Back out the screws on the receptacles and connect to the screws. Or stick a screw driver into the Ground "hole" on the receptacle.

I can go on, but not sure exactly what your lookin for.

mke

[daman1]

Hey GWJ. You don't sound like your average public locator. Where did you learn your trade from ? Is there formal training available to an educated/motivated locator in this field?

[GWJ_CAS]

Hey GWJ. You don't sound like your average public locator. Where did you learn your trade from ? Is there formal training available to an educated/motivated locator in this field?

I am an owner of an engineering firm that specializes in subsurface utility engineering, one call locating and exotic, high-tech locating. I also own a utility construction services firm and an equipment sales firm that sells locating and leak detection equipment. We believe in outfitting our locators with the full arsenal of tools. All of our locators have at least two EM systems, a GPR system, leak detection equipment, hydrophone, ferro-magnetic locator and any other tools they may need in their truck...We primarily use Metrotech i5000's and Vivax Vloc Pro's for EM equipment (we sell them too), Mala GPR systems, IDS Detector Duo GPR systems (we sell them too), Metrotech 880B ferro-magnetic wands, Metrotech Hydrophone, Ground Mics, Loggers and Correlators (we sell all these too).

Been doing this 24+ years and it is just what we do and how we decided to do things...

[FreedMan]

Thanks for the input folks. The first job went down this morning and went well. Turned out to be less involved than anticipated. The one next week will be a little more involved, but should not be a problem.

GPR is off the table because it's not in my budget just yet (ya gotta start somewhere), maybe once we get rolling and a bit more financially secure we can look into adding that tool to the box.

I've been doing this for most of two decade now and mainly wanted to compare a few notes and make sure I hadn't forgotten anything really important. Looks like I was on the right track.

Thanks again for the input.

[Goldenboy]

If you have a big job in the works you can always demo a GPR unit. Alot of times they'll send one to use for a couple weeks to try to get you to buy theres.

[FreedMan]

Now there's an idea I hadn't considered. Good point. Thanks.