Technical Bulletin
Beneath Concrete

INTRODUCTION

Here at Delta Geophysics we feel it is an important part of our business to inform our clients about proper geophysical survey techniques and practices so that you can maximize survey results. The following is a brief discussion explaining how a geophysical survey should be conducted to identify anomalies beneath metal-reinforced concrete.

 

OVERVIEW

Typically the signal from Ground Penetrating Radar is shielded by the metal reinforcement in the concrete and provides little, if any, real information beneath the reinforcement. The basic metal detector only detects the metal reinforcement in the concrete; it cannot discriminate the signal produced by a reinforced slab or a UST beneath a reinforced slab. Under these circumstances, an EM‐61 survey may be the best answer. The Geonics EM‐61 is a time‐domain metal detector which detects both ferrous and nonferrous metals. Because of the strength of it’s signal and the broad-band recording capabilities of the data logger, much information is contained in the EM-61 signal response. This broad-band signal, when recorded and processed properly, can discern anomalies beneath reinforced concrete. Specialized field procedures and adaptive filtering techniques used by Delta often reduce the near-surface influence of a reinforced slab allowing the detection of targets underneath. Delta’s field geophysicist further processes the signal using

interactive target editing and grouping tools for final target list refinement. Processed and contoured data can then be displayed on site maps for visualization and field referencing.

Delta maintains state-of-the-art mapping capabilities in various software platforms to provide seamless integration with your existing engineering drawings, or to provide turnkey site mapping solutions plans for you. We have attached an example of an EM‐61 survey at a gas station with the site features mapped by Delta and displayed in graphic format.

Like all geophysical methods an EM‐61 survey has limitations and may not provide conclusive evidence for anomalies below reinforced concrete. But this instrument can be an effective technique to locating metallic masses beneath reinforced concrete when used by experienced personnel.

Delta has the knowledge, both through experience and forward modeling, to evaluate client needs and offer consultation regarding geophysical applications. Give Delta a call today to learn how our experience can be applied to your project.