Ground characterization using cross-hole radar: ZOP configuration in weathered limestone

A borehole transillumination GPR survey conducted using zero offset profiling was performed at a geotechnical test site in central Florida to characterize subsurface conditions. These conditions consist of approximately 6 meters of clayey/sandy-clay soil overlying variably and highly weathered limestone. The test site has five PVC cased boreholes arranged in a "plus sign" (+) pattern aligned roughly in an east-west and north-south direction with each borehole spaced approximately 3 meters apart. The depth of each borehole is approximately 18 meters. The GPR survey was conducted along the east-west direction. The radar velocity results from the GPR survey clearly show a transition between soil and weathered bedrock and the effect of the water table on radar velocities. The radar velocities within the limestone clearly show two distinct limestone zones; an upper highly weathered zone with relatively low radar velocities and a lower less weathered zone with relatively high radar velocities. The interface between the two distinct zones occurs at different depths within the boreholes. The radar velocities recorded in the limestone are much lower than typical published values for limestone but are the very similar to radar velocities from other studies in highly weathered limestone.