Predicting landslide stability, runout, and failure velocity at Cook Lake landslide, Wyoming
AuthorScheevel, Caroline R.
AdvisorSanti, Paul M. (Paul Michael), 1964-
MetadataShow full item record
AbstractProper understanding of risk is predicated on accurate characterization of hazard. Landslide hazards are common, but are difficult to characterize without a full site investigation, which are often unavailable. This thesis develops a framework for obtaining inexpensive field and laboratory data to characterize three major components of landslide hazard: current stability, runout distance (L), and failure velocity. The framework is designed to analyze deep-seated, soil landslides, and is evaluated using data from the Cook Lake, Wyoming landslide. The framework consists of four tools. Two of these are flowcharts that predict both catastrophic runout and velocity. In line with runout predictions, the third tool estimates the ratio of landslide drop height to runout length, H/L, from measurements of planimetric area. The final tool utilizes back analysis and forward modeling to evaluate a slope’s stability and its sensitivity to hydrologic changes, relying on multiple analyzed sections and sensitivity analysis in lieu of detailed subsurface data. The two flowcharts were developed by synthesizing literature about landslide geometry, local topography, and pore-water pressure. The H/L estimation tool correlates the planimetric area of well-characterized landslides to landslide mobility. The stability modeling tool uses fieldwork, direct shear testing, and limit equilibrium analyses to characterize the behavior of the geologic materials. Comparison of the backward model, which evaluated conditions that triggered a 1997 landslide at Cook Lake, to the forward model revealed that portions of the landslide are more unstable than they were in 1997. Estimates of H/L for a future reactivation range from 0.17 to 0.25. The runout flowchart also indicates that the landslide is likely to exhibit H/L > 0.1, though unexpected contractive soil behavior might cause long runout. The velocity flowchart indicates that the landslide is not likely to move faster than 1.8 m/hr. The combination of these slower velocities and shorter runout indicators would allow evacuation of a nearby campground at Cook Lake during a future reactivation. Other similarly vulnerable sites can benefit from these tools.
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Development of a landslide risk rating system for small-scale landslides affecting settlements in Guatemala CitySanti, Paul M. (Paul Michael), 1964-; Faber, Ethan J.; Higgins, Jerry D.; Zhou, Wendy; Stouth, Alex B. (Colorado School of Mines. Arthur Lakes Library, 2016)Many settlements in the Guatemala City Metropolitan Area (GCMA) face significant possibilities of fatalities due to their location in steep ravines that are subjected to periodic large-scale landslides. Since the housing in the at-risk areas is relatively low-cost, it is typically cost-prohibitive to mitigate the risk to an acceptable level. Thus, permanent relocation is the only truly viable option to ensure the long-term safety of everyone. However, there are several economic and social obstacles impeding successful implementation of a relocation program. Still, there are many other landslide risk reduction techniques (such as retaining walls, community drainage systems, and alert systems) implemented by government organizations and non-profit groups. These techniques are helpful in landslide risk reduction (LRR), but residents are only partially involved in the entire process. Therefore, increasing residents’ education and ability to better understand their level of landslide risk will help with LRR. Residents can integrate and collaborate with the government organizations and non-profits implementing mitigation techniques and of even greater benefits, the education and ability for residents to understand their landslide risk can provide additional avenues for LRR not otherwise achievable. The purpose of this research is to develop a landslide-risk-rating-system (LRRS) that can be used by trained residents to better understand their risk (similar to other landslide or rockfall hazard-rating systems commonly used by department of transportation organizations). The focus of this LRRS is only on small-scale landslides (typically the size of a house or less) because evaluating the risk of large-scale landslides is too complicated to be done by trained non-technical experts. The LRRS asks questions related to landslide risk that can be used to calculate a landslide risk score to indicate the relative level of risk. The LRRS was created by reviewing published literature documenting other landslide rating systems and incorporating similar factors correlated with landslide risk. Then, forty sites were visited in the GCMA to inventory the factors at houses that are vulnerable to landslides in order to evaluate which factors were most useful for predicting the relative risk. The predicted risk scores were compared to ranked risk scores estimated by the author to ensure the results were valid. Statistical analysis identified which of these factors best-predicted landslide risk. These factors include slope angle, slope height, strength of slope material or material type, aperture of cracks, spatial impact, largest probable landslide volume, largest probable percentage of the living area that could be impacted from a landslide, and total person-hours a living area is occupied per day. Future work should focus on the transformation of the tool into a more user-friendly format for use by residents, the implementation process, and monitoring plan.
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