ABSTRACT:

Floyd Hill is a section of Interstate 70 (I-70) of great importance, due to high volumes of traffic from Denver entering and returning from the Rocky Mountains being required to pass through this stretch. The rock slope in this section has been recommended for monitoring by the Colorado Department of Transportation (CDOT), as its susceptibility for rockfall and proximity to the roadway make it a potential threat to the operation of this stretch of highway. A goal of rockfall monitoring at Floyd Hill is to further understand rockfall activity and its relationship with common environmental triggers, which help in the identification and mitigation of rockfall hazard and/or risk. This study evaluates rockfall activity at Floyd Hill over two years using terrestrial LiDAR to quantify rockfall volumes and the number of rockfall events. A semi-automated workflow is utilized to convert raw point cloud data into a rockfall database that inventories rockfall events. The semi-automated workflow makes it possible to reduce the amount of processing time and manual effort required to create a usable rockfall database, subsequently allowing for analysis of high temporal resolution LiDAR data. We conclude that over the analyzed period, the greatest volumes of rockfall occurred between April and September of 2019. Outside of this period of time, however, the rockfall frequency remained consistent throughout the remainder of the study period.

1. Introduction

Rockfall frequency has been shown to follow seasonal trends by numerous studies, as common climatic rockfall triggers (rainfall, snowmelt, freeze/thaw, etc.) occur on a seasonal basis (Douglas, 1980; Matsuoka and Sakai, 1999; Delonca et al., 2014). Previous studies have used a variety of methods to evaluate the distribution of rockfall activity and rockfall triggering mechanisms in specific geographic areas. Fallen rocks have been collected within a defined area and measured by hand (Douglas, 1980; Matsuoka and Sakai, 1999), photographic methods such as time-lapse photography, stereographic pairs, and aerial image analysis have also been utilized to identify changes in rock slopes (Frayssines and Hantz, 2006; Zwissler et al., 2013; Matsuoka, 2019), dendrochronology has been used to analyze historical seasonal or yearly trends in rockfall activity (Stoffel et al, 2005; Zielonka and Wronska-Walach, 2019), and reports and measurements provided by transportation authorities and other governing bodies have been analyzed (McCauley et al., 1985; Delonca et al., 2014).

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