Cavity detection — an engineering application for gravity

Gravity surveys, as applied to geotechnical engineering problems, have been extensively used as a method for the detection of cavities. Through careful data analysis and modern presentation techniques, a much better overall geological model can be derived. A case history is presented from the Thompsons Creek Dam Site, NSW which illustrates that the gravitational method, through the careful use of standard survey procedures and equipment, has potential as a geological mapping tool in urban or industrial settings deemed inappropriate for other techniques due to environmental issues or geophysical noise considerations. Rock density determinations based on regression analysis of gravity data detected significant anomalies over the survey area. Image processing was used to enhance Bouguer gravity intensity maps, which enabled the location of additional cavities in the vicinity of the proposed dam site.