ROCKFALL HAZARD ASSESSMENT USING DIGITAL GEOSPATIAL DATA AND SMART ROCK TECHNOLOGY

Rockfall from highway rock cuts presents a potential hazard to transportation systems in New Hampshire. Rockfall onto roads may cause driving hazards for motorists as well as damage to property and infrastructure. Conventional techniques to evaluate rock slopes consist of engineering and geologic assessments of slope stability using manual data collection, topographic maps, and precise GPS surveys. Modern analysis techniques using digital data can greatly increase the structural detail available for use in assessments. Unfortunately, higher priorities and the expense of data acquisition mean very few of the approximately 380 rock cuts in New Hampshire have been digitally modeled for comprehensive slope stability or rockfall analysis.

Newer geospatial data sets, such as digital elevation models (DEMs), photogrammetry from unmanned aircraft systems, and ground-based lidar, provide unique opportunities to model rock slopes with greater accuracy. Recently, high resolution ground-based lidar has been used for detailed characterization of rock slopes by the Federal Highway Administration, but this has only been acquired for one rock cut in New Hampshire. High resolution photogrammetry data sets are also not widely available due to the cost and time requirements of data acquisition. However, DEMs of varying resolutions are freely accessible for most of the state of New Hampshire through NH GRANIT and the NH Department of Environmental Services.

Two case studies compare the uses of DEMs in New Hampshire for rock cut assessment. In Londonderry NH, project-level survey data from highway construction are compared to DEM and photogrammetry cross sections. The advantages and disadvantages of each data type are demonstrated and discussed. In Durham NH, rockfall models using digital data are compared to experimental data from the University of New Hampshire’s Smart Rock. The Smart Rock, placed inside a real rock, tracks acceleration during a rockfall. Research is continuing in order to investigate if easily-available digital data and measurements from smart rocks can be used to better understand the hazards posed by rock cuts across New Hampshire’s highways.