CorBuilt LLC offers Ground Penetrating Radar and Electromagnetic Induction surveys for utility location and other subsurface items such as buried tanks or drums. Due to a variety of site conditions there can be limitations to the effectiveness of the equipment. It is widely acknowledged that these limitations can, on some occasions, result in a less than accurate survey. In some cases, either one or both systems may be completely ineffective. This may result in relying on one system only or terminating the survey entirely. In good conditions, the two systems work best together to confirm the existence and accuracy of targets seen by both machines. CorBuilt LLC will in all cases attempt to communicate any conditional limitations or problems with
the survey. It is optimal for the client to plan a physical walk through of the site after the survey in order for the technician to explain all of the aspects of the markings, flags, and answer any questions about the conditions, etc. The collection, interpretation, and reporting of our data is relevant only to the job scope we have agreed to and does not entail any engineering, structural engineering, geological, or survey grade land surveying documentation.
Due to these limitations and possible inaccuracies CorBuilt LLC CANNOT AND WILL NOT GUARANTEE 100% ACCURACY OR THAT ALL UTILITIES OR STRUCTURES HAVE BEEN LOCATED AND MARKED. The decision to proceed with saw cutting, drilling, or other construction or investigation procedures is entirely up to the client or site owner and the client or site owner assumes all risk.
CorBuilt LLC will not be responsible for the maintenance of the markings. How long the markings last is determined by weather, site conditions, traffic, etc., and CorBuilt LLC will not guarantee how long they will last. CorBuilt LLC will be available to redo the markings or the entire survey, if necessary, at additional cost.
A survey by CorBuilt LLC does not constitute or replace a CBYD, Dig Safe, or any other law mandated local service call. CorBuilt LLC is not and will not be responsible for calling or scheduling these services. This responsibility is the clients or others.
Equipment and Limitations
Ground Penetrating Radar and Electromagnetic Induction are the primary tools used for both subsurface and concrete scanning surveys. Both systems are susceptible to site conditions that can result in false negatives or positives. In these cases, there is the possibility that a marked utility is not there, or an existing utility is not marked.
Ground Penetrating Radar
Site conditions that limit the GPR equipment range from soil types and conditions, water table and other moisture content issues, and surface conditions. The Radar equipment consists of an antenna mounted to the bottom of a stroller. The antenna needs to ride along in constant contact with the ground. Therefore, any rough terrain, like small stumps from brush cutting, bushes, and any large debris can interfere with the survey. Water and other sources of moisture disburse the electromagnetic radar signal resulting in the inability to “see” through water tables or standing water. Some soil types like clay, iron rich soil layers, and others can also interfere with GPR. Client agrees to stay no less than thirty-six inches (36”) away from CorBuilt markings unless otherwise specified.
Electromagnetic Induction (EMI)
Electromagnetic Induction is also susceptible to interference from many of the same conditions as GPR. In using EMI, a transmitter is placed on the ground, and an electromagnetic signal is broadcast into the ground at a specific frequency. When this signal encounters a metal pipe or wire, that signal is carried along that target like an antenna. The technician, with a wand built to receive that specific frequency, can follow and mark that target. There are many complex situations that can occur with this equipment that can result in inaccurate markings. In busy areas that have numerous targets, a larger target may emit a stronger signal resulting missing a smaller target nearby. There are too many other difficulties with this technology to go into all of them here. Client agrees to stay no less than thirty-six inches (36”) away from CorBuilt markings unless otherwise specified.
The issues with both GPR and EMI regarding concrete scanning generally involve reinforcement. The mixture of utilities and reinforcement in concrete and trying to isolate one from the other is extremely difficult. With EMI, the broadcasting of the signal into the concrete means that all the metal reinforcement will carry the signal as well as the utilities. Even when inducing a signal directly to a pipe or wire, those utilities may have been grounded to the building steel or the reinforcement, and the signal will be carried erratically all over the place. GPR cannot discern the difference between a pipe or conduit from reinforcement. Client agrees to stay no less than two (2”) away from CorBuilt markings unless otherwise specified.
CorBuilt LLC utility surveys include site markings only. Usually Paint, pin flags, or other agreed upon marking systems. CorBuilt LLC GPS services can be added to your contract at additional cost. We can provide KMZ (Google Earth file) or CAD drawing. Our CAD drawings will be generated on a base drawing of your site supplied by you. CorBuilt LLC documentation files and drawings are informational only and are not professional survey grade materials. CorBuilt LLC is not a licensed land survey company, and the deliverables from our GPS services should not be construed as such.