HAZARD ANALYSIS OF A SEGMENT OF HIGHWAY SR-12 THROUGH BRYCE CANYON NATIONAL PARK

Over 2.6 million people travel each year along National Scenic Byway SR-12 which is a major thoroughfare for tourists traveling to Bryce Canyon National Park (BCNP), Grand Staircase-Escalante National Monument, and other scenic attractions in Southern Utah. SR-12 is susceptible to rockfall and landslide hazards where it descends from the Paunsaugunt Plateau into Tropic Canyon. These hazards can lead to economic loss due to travel delays for tourists and commodities, and possible loss of life. Rockfall could have devastating effects on SR-12 because of the traffic volume, sharp turns, low visibility, and steep drop-offs. A landslide near milepost 15 on SR-12, on the northern end of BCNP, prompted emergency repairs in 2017 that cost over $2.6 million dollars.

SR-12 runs below a cliff band of the relatively weak Tertiary Claron Formation limestones and mudstones that make up the colorful hoodoos and erosional features of Bryce Canyon. The Oligocene- to Miocene-aged Ruby’s Inn Thrust Fault (RITF) has juxtaposed resistant beds of Claron Formation over weaker beds of Claron, creating the cliff band above the roadway. The research hypothesis is that the RITF and associated fracturing have weakened the rocks in this cliff band creating a rockfall hazard. Research objectives are to examine the fracture characteristics using scanline techniques similar to Watkins et al. [Journal of Structural Geology, 72 (2015) 67-82] and measure the geometry and physical properties of the toe slope (runout zone) to assess rockfall potential and identify contributing factors for hazards along the highway. Lab testing will be performed to assess physical characteristics of the rock, soil, and fracture filling. Rock mechanics, fracture filling composition, fracture spacing, and orientation will then be used to perform kinematic analyses for the cliff band to assess failure potential. Rockfall analyses will be performed to assess the probability of rocks reaching the roadway after failure.