APPLICATIONS OF INTEGRATED GEOPHYSICAL SURVEY IN DEFINING SUBSIDENCE FEATURES ON A GOLF COURSE

Abstract

Subsidence was observed at several places on the Salina Municipal Golf Course in areas known to be built over a landfill in Salina, Kansas. High-resolution magnetic survey (57,900 ft2), multi-channel electrical resistivity profiling (three 504-ft lines), and microgravity profiling (23 gravity-station values) were performed on a subsidence site (Green 16) to evaluate the effectiveness of the geophysical methods in determining boundaries and density deficiency of the landfill in the vicinity of the subsidence. Horizontal boundaries of the landfill were confidently defined by both magnetic anomalies and the pseudo-vertical gradient of magnetic anomalies. Furthermore, the pseudo-vertical gradient of magnetic anomalies presented a unique anomaly at the surface of Green 16, which provided a criterion for predicting other spots with subsidence potential using the same gradient property. Results of multi-channel electrical resistivity profiling (ERP) suggested a bottom limit of the landfill at Green 16 was around 70 ft below the ground surface based on the vertical gradient of electric resistivity and a priori information on the depth of the landfill. ERP results also outlined several possible landfill bodies based on their low resistivity values. Microgravity results suggested a –0.14 g/cm3 density deficiency at Green 16 that could equate to future surface subsidence as much as of 5 ft due to gradual compaction.