Analysis of Slope Failures Along Alabama Highways

Abstract

Slope stability management systems (SSMSs) have been developed by multiple state transportation agencies to assess landslides adjacent to highways—aiding in the effective allocation of resources for slope and/or roadway repairs. The Alabama Department of Transportation (ALDOT) does not have a SSMS which may hinder its ability to effectively manage landslide hazards. This thesis discusses the development and analysis of two SSMS components for ALDOT: the data collection system (Slide Spread), and the asset management system (the Landslide Hazard Prioritization system (LHPS)). The data collected within Slide Spread were used to determine common trends and similarities between landslides and environmental factors, as well as between landslides and other landslides. The research identified geologic units with higher likelihoods of landslide events, as well as the impact of precipitation within the region. The Tuscaloosa Group, Midway Group, and Selma Group Chalk had a higher likelihood of landslide events along roadways. Whereas, slides were less likely to occur in limestone dominated regions. 25% of the landslides analyzed occurred within 1000 feet of converging geologic groups, possibly indicating regions of weaker soils near joints or boundaries. The rainfall analysis illustrated the number of slides within a region generally increased with increasing precipitation. However, few slides occurred within limestone dominated regions despite the amount of rainfall experienced. In addition, Slide Spread was used to compare common landslide attributes. Approximately 40% of landslides occurred at or adjacent to a past failure, indicating possible weak soils located at joints and boundaries. 61% of slides occurred within fill sections along the roadway, displaying possible compaction flaws within their construction. 30% of landslides were located near culverts—however the number of failures at damaged and undamaged culverts were relatively equivalent. The majority of slides within the database were classified as either translational failures or shallow failures. Translational failures were likely triggered by to rainfall events, leading to slip surfaces within the slopes. The shallow failures consisted of failures within the fill and cut sections, as well as failures due to erosion. The LHPS is a landslide rating system used to determine and rank the impact of a landslide on the adjacent roadway and the traveling public. The system determined Morgan, Bullock, Etowah and Macon Counties had the highest hazard score ratings, and I-85 was the roadway most affected by the landslides. The system does not currently consider the accident history along the roadway, maintenance frequency, length of roadway impact, or precipitation—which should be added in future studies. The results of this research will allow ALDOT engineers to better plan and mitigate roadway impacts from landslides.