Power Main under Slab-on-Grade
Meeting room where power supply line was located adjacent power panel area. Conquest screen shows real-time mapping data from the power cable (PCD) sensor.
Overview
A recent building renovation required mapping the precise location of the main power line entering the building under the slab-on-grade floor. Conquest with PCD (Power Cable Detection) provided a quick and easy solution.
Problem
Many low rise buildings with concrete slab-on-grade floors have poor documentation of utility connections that were placed under the slab. GPR provides a powerful way of mapping out the sub-slab installations. In this case study, the lead-in from the street to the building was not well defined at the front of the building. The power feed disappeared under the concrete floor and emerged at a panel in the center of the building.
GPR Contribution to Solution
The contractor selected a Conquest concrete imaging GPR with a PCD (Power Cable Detector) sensor to attempt to locate the power cable path. A major benefit of the Conquest approach was the speed of data acquisition and the fact that very little disruption was required to day-to-day business activity. The added benefit of the integrated PCD sensor that can detect live power cables simplifies data analysis.
An initial 8' x 8' Conquest grid was established in a meeting room adjacent to the power panel since this was the probable route for the cable. The PCD data were collected simultaneously with the GPR data and the results superimposed on a floor plan as seen below.
The GPR data defined tha slab reinforcing and gave a suggestion of a deeper feature. The PCD data were very definitive and clearly showed the presence of the power cable alignment as show below.
GPR and PCD imaged data superimposed on building floor plan. The GPR data (left) shows the distribution of the reinforcing in the slab-on-grade. The PCD response (right) shows the classic lozenge-shaped response of a twisted parallel wire.
With this initial result in hand, a series of smaller grids and traverse lines were run in the rest of the room and the next adjacent room. The power line was even mapped on the sidewalk outside and tied into the utility street locate marks.
Results & Benefits
The use of Conquest GPR with PCD demonstrates the power of combining multi-sensor data to solve a practical day-to-day construction problem. Some key benefits are:
- Conquest operation is simple and intuitive
- Users can be effective with only a few hours of training
- The integrated GPR and PCD provide a high level of confidence in the postioning of live power cables
- Systematic search protocols are available as best practice guides
- Grid mapping with superposition of depth images on as-build or floor plans simplifies data analysis and reduces poor interpretations
GPR responses vary greatly depending on the target being sought and the host material. GPR response variability can be challenging to new GPR users. When learning about GPR, the best practice is to review several similar case studies to develop an understanding of variability. Check for other insightful information on the resources tab to learn more. Use Contact Us or Ask-the-Expert to reach our Application Specialists who can help you tap into Sensors & Software's vast array of technical information.