MAGNETICS AS A TOOL FOR URBAN SITE CHARACTERIZATION, SHREVEPORT CONVENTION CENTER, LOUISIANA

The re-use of existing sites is growing increasingly important for urban revitalization and prevention of urban sprawl. An extensive magnetic gradiometer survey was conducted using a Geometrics G-858 magnetometer on a previously occupied urban industrial site to locate objects in the subsurface prior to construction of the new Shreveport Convention Center in Louisana. The site contained numerous types of magnetic material both on the surface and hidden in the subsurface.

To map the distribution of surface and buried magnetic material, two cesium vapor total-intensity magnetometers were mounted on an aluminum pole at 2.1m and 1.2m of elevation. The elevation difference between the magnetometers was used to indicate the depth of a buried object by observing the magnetic field “fall-off” between the anomalies generated when magnetic materials were present. A large “fall-off” will signify small near-surface metallic artifacts and a small “fall-off” indicates larger magnetic objects at greater depth.

Three large areas were surveyed. The old railroad station in Area 1 was a high noise area due to railroad tracks, large metallic refuse, and reinforced concrete. Area 2 was the largest section located adjacent to Caddo Street. This area was the least cluttered and produced a very clean magnetic section with easily discernible artifacts. Area 3 was adjacent to an excavated pit that allowed us to ground-truth our findings with pipelines at known depths.

From the data gathered in this study we were able to identify objects in the subsurface and determine where excavation would be difficult. Area 3 revealed two large magnetic anomalies that require further investigation in order to avoid possible construction delays. We were also able to determine areas where caution should be exercised near buried utilities and void spaces. Magnetic surveying has been shown in this case to be a viable technique for urban site characterization prior to redevelopment.