Infrasense Recently Performed GPR Survey to Verify the Construction of a Concrete Pier at the Midway Airport in Chicago

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Infrasense, Inc. completed a ground penetrating survey (GPR) to map the size and position of the steel reinforcing mesh within an undocumented pier extension at the Midway Airport in Chicago, IL.

Midway Airport in Chicago

GPR was brought in to identify the reinforcing steel pattern, determine the rebar thickness, and identify the depth of the caisson supporting the fourth column.

Infrasense Inc., one of the leading subsurface detection firms in the nation, recently completed a ground penetrating radar (GPR) survey to map the size and position of the steel reinforcing mesh within an undocumented pier extension at the Midway Airport in Chicago, Illinois. The pier itself was originally designed as a three-column structure, but was constructed as a four-column structure without updated as-built information being recorded. Concerns over the structural effectiveness were raised, and GPR was brought in to identify the reinforcing steel pattern, determine the rebar thickness, and identify the depth of the caisson supporting the fourth column.

GPR was the preferred method for this survey because of its ability to accurately measure the location and depth of objects within a material (concrete) without the need for cutting, drilling, or coring. The method is readily mobilized and provides real time information that can be used by the client for immediate verification and scope of work changes. To identify the rebar construction a 1.5-GHz GSSI GPR antenna was used to collect a series of bi-directional lines spaced at 4-inches apart in the vertical direction and 6-inches apart in the horizontal direction. The GPR survey covered four sides of the concrete pier. A 400-MHz antenna was used to map the depth of the caisson by collecting parallel lines surrounding the pier column. The data collection was completed in approximately 4-hours, using equipment that was hand carried to the project area.

Ground penetrating radar operates by transmitting short pulses of electromagnetic energy into a concrete structure using an antenna that is moved across the surface. These pulses are reflected back to the antenna with an arrival time and amplitude that is related to the location and nature of dielectric discontinuities in the material (e.g. reinforcing steel). For the concrete pier, GPR measured the reflected response of the reinforcing steel, which was used to map the position and size. The results of our survey were significant as they provided crucial structural information about the integrity of the pier extension, and whether repairs or reconstruction is necessary.

About Infrasense, Inc.

Since 1987, Infrasense, Inc. has applied state-of-the-art technologies to address the most difficult challenges in subsurface scanning. Infrasense’s engineers can nondestructively extract critical information from a diverse range of structures. In addition to providing ongoing subsurface evaluation services to clients across the country, the firm has also conducted numerous research programs to advance the field of subsurface detection and non-destructive evaluation. To learn more about Infrasense and the services we provide, visit our website: http://www.infrasense.com

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Lori McCormick
Keith Sorota

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