What is Electromagnetic Induction (EMI)
Electromagnetic Induction (EMI) is used to create profiles of the subsurface. A signal is sent from a transmitter coil where it radiates into the ground generating currents within the ground. Those currents produce secondary signals that are detected on the surface by a receiver coil. The larger the distance between the coils the deeper the current can reach.
Another exciting job has drawn to a close. Encompass Inspections was able to witness the excavation work in action out at the Serape Cotton Gin site and the findings were astounding.
A few weeks ago, Encompass Inspections was called upon to perform a survey of a very large property that historically was filled with sub grade buildings, tanks, canals and other debris. We decided to utilize Electromagnetic Induction (EMI) to complete the work. This technology was chosen above others because the scope of work would require roughly 20ft of penetration into the ground. We began by creating a grid system that would work for our equipment and also helped us plot the anomalies located for future removal by excavators. We decided to create 12 quadrants where most of the quadrants were 300’ by 300’ sections. Each quadrant was then divided again into ten, 30’ wide rows that were 300’ long. In each quadrant, a 150’ marker was placed halfway down each row. Once the quadrants were established, we began scanning each quadrant, row by row.
As the data is logged into the hand held control unit, the operator can see real-time results of the EMI and a marker was placed at the location of the anomaly. After the survey of the entire lot was completed, the entire data log is then downloaded onto a computer where a program is able to plot the data on the X and Y axis. This technology allows 3D imagery to be rendered of the surveyed area depicting the size and conductivity of the anomaly.
After viewing the data on the computer, it was simple to then go back to the targeted anomalies and reanalyze them using other forms of technology. In some instances, we were able to use Ground Penetrating Radar (GPR) to locate smaller anomalies like small conduit or PVC pipes that were not conductive enough for EMI. We then logged the data that was produced through GPR and overlaid that on top of our EMI map and created a survey profile. Encompass Inspections then provided highly detailed images and maps for the client to assist in the locating of these anomalies. Each possible anomaly that was located by Encompass Inspections turned out to be a very accurate rendering of what was below the surface.
The excavators called us later to thank us for having helped them find 22 large truckloads of extra buried debris that was not known to exist.