HIGH RESOLUTION SENSING TECHNIQUES FOR SLOPE STABILITY STUDIES

The National Bureau of Standards (NBS), in conjunction with the U.S. Geological Survey (USGS), conducted a four-phase evaluation of high resolution remote sensing techniques for application to problems of determining slope stability. The first two phases, for which the USGS was chiefly responsible, concentrated on documenting the subsurface features and associated characteristics which determine or influence slope stability. In phase three, the NBS surveyed a variety of electromagnetic and acoustic remote sensing techniques which exhibited the greatest potential for detecting the subsurface features and chharacteristics and which satisfied the Federal Highway Administration (FHWA) conditions of availability, practicality and portability. Two techniques were chosen for further experimental and developmental pursuit: the existing FM-CW radar system, and the plannar near-field reconstruction (PNFR) approach, respectively. In phase four, the existing FM-CW radar system was applied and analysed in a series of field experiments to determine the subsurface structure at a designated test site in the Pike National Forest south of Denver, Colorado. Local and regional subsurface conditions for the test site were mapped and a detailed geologic section of the site was produced from core samples taken from four boreholes drilled into the subsurface granite. The FM-CW system, which has displayed considerable success in the past for the subsurface granite. The FM-CW system, which has displayed considerable success in the past for locating near-surface anomalies, accurately revealed a joint at a depth of 6.5 meters which was confirmed by the core data. The PNFR technique, which is still in the devleopment stage at NBS and is based on an effective utilization of the exact holographic or near-field equations, was also pursued to the point of running computer simulated experiments. Preliminary results for the detection of small subsurface anomalies by the PNFR technique have been highly encouraging. /FHWA/