Ground-Penetrating Radar Investigations
Large Residential Developments
AGI completed separate GPR investigations of subsurface cavities at two large residential developments located on the west and east sides of the Las Vegas Valley. Grading activities at these two sites exposed bedrock solution cavities. To help investigate the extent of these cavities, AGI conducted GPR surveys on over 100 acres of graded building pads positioned along the anticipated trend of these fracture pattern-related cavities.
At the west valley site we recorded both 200 and 80-MHz GPR profiles to investigate the upper 40 feet of the ground surface for cavities. GPR profiles such as the 200-MHz profile shown below revealed areas where cavities or other changes in bedrock conditions occurred. Our client completed boreholes and excavations across these areas where GPR anomalies were detected. This geologic information was used together with the GPR profiling results to help map the extent of subsurface cavities at this site.
At the east valley site we recorded 200-MHz GPR profiles along survey lines spaced 3-feet apart. This higher density of survey data coverage was used to prepare 3D GPR data volumes (using the GPR-Slice™ processing software). These 3D GPR data volumes were sliced along horizontal planes at various depth intervals to produce a succession of map view images of the radar reflection amplitude variations across the survey area. The resulting map view images such as those shown below were used together with conventional 2D GPR profiles to interpret the locations of possible bedrock cavities. The possible cavity locations were further investigated by borehole measurements.