USING GOOGLE EARTH'S STREET VIEW TO RATE CUT SLOPES ALONG HIGHWAYS WITH RESPECT TO ROCKFALL HAZARDS

Rockfall hazard from cut slopes along highways are primarily caused by unfavorable orientations of discontinuities or undercutting of strong rocks by weak interbedded rocks. A rockfall hazard rating system (RHRS) was first introduced in Oregon in 1987 to rate cut slope’s potential for releasing rockfalls. Various state DOTs have fully adopted the RHRS or modified it to fit local conditions. RHRS is a numerical score-based rating of parameters such as slope geometry (height, angle, roughness, orientation), driver’s line of sight, climate, and geologic data (discontinuity characterization). This data is traditionally collected using a line survey method at the site. The method is time consuming, expensive and can be dangerous. The purpose of this study is to test the use of Google Earth and its street view tool to remotely collect data for RHRS purposes for selected parameters. The selected parameters had to be measureable using Google Earth. Each of the selected parameters was rated according to the original RHRS and the version modified by Colorado’s DOT. The set of selected parameters include slope parameters (height, angle, aspect, roughness, and catchment ditch width), driver’s line of sight, and a visual assessment for the likelihood of structurally controlled or undercutting-induced rockfalls. A section of Route 33 in Virginia with a high density of road cuts, located close to the western border of Virginia, was selected for the study. 41 individual sites were evaluated along a 3.5 mile section. Sites were evaluated by using a combination of measurement tools available in Google Earth’s overhead view and a visual inspection of the rock units in street view. Catchment ditch widths estimated from Google Earth’s street view were rated based on the results of computer-based rockfall simulations which was modeled for conditions observed in the field. The results showed rating scores ranging from 147 to 410, where the maximum possible score is 891. This method is performed remotely on a desktop allowing a fast, economical and safe rating of cut slope’s hazard with respect to rockfall generation.