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Deciphering Landslide Behavior Using Large-Scale Flume Experiments Mark E View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Digital Repository @ Iowa State University Masthead Logo Geological and Atmospheric Sciences Conference Geological and Atmospheric Sciences Presentations, Posters and Proceedings 2008 Deciphering Landslide Behavior Using Large-scale Flume Experiments Mark E. Reid United States Geological Survey Richard M. Iverson United States Geological Survey Neal R. Iverson Iowa State University, [email protected] Richard G. LaHusen United States Geological Survey Dianne L. Brien United States Geological Survey See next page for additional authors Follow this and additional works at: https://lib.dr.iastate.edu/ge_at_conf Part of the Hydrology Commons, and the Soil Science Commons Recommended Citation Reid, Mark E.; Iverson, Richard M.; Iverson, Neal R.; LaHusen, Richard G.; Brien, Dianne L.; and Logan, Matthew, "Deciphering Landslide Behavior Using Large-scale Flume Experiments" (2008). Geological and Atmospheric Sciences Conference Presentations, Posters and Proceedings. 3. https://lib.dr.iastate.edu/ge_at_conf/3 This Conference Proceeding is brought to you for free and open access by the Geological and Atmospheric Sciences at Iowa State University Digital Repository. It has been accepted for inclusion in Geological and Atmospheric Sciences Conference Presentations, Posters and Proceedings by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Deciphering Landslide Behavior Using Large-scale Flume Experiments Abstract Landslides can be triggered by a variety of hydrologic events and they can exhibit a wide range of movement dynamics. Effective prediction requires understanding these diverse behaviors. Precise evaluation in the field is difficult; as an alternative we performed a series of landslide initiation experiments in the large-scale, USGS debris-flow flume. We systematically investigated the effects of three different hydrologic triggering mechanisms, including groundwater exfiltration from bedrock, prolonged rainfall infiltration, and intense bursts of rain. We also examined the effects of initial soil porosity (loose or dense) relative to the soil’s critical- state porosity. Results show that all three hydrologic mechanisms can instigate landsliding, but water pathways, sensor response patterns, and times to failure differ. Initial soil porosity has a profound influence on landslide movement behavior. Experiments using loose soil show rapid soil contraction during failure, with elevated pore pressures liquefying the sediment and creating fast-moving debris flows. In contrast, dense soil dilated upon shearing, resulting in slow, gradual, and episodic motion. These results have fundamental implications for forecasting landslide behavior and developing effective warning systems. Keywords Landslide, experiment, failure behavior, hydrologic trigger, critical state, porosity Disciplines Hydrology | Soil Science Comments This proceeding is published as Reid, Mark E., Richard M. Iverson, Neal R. Iverson, Richard G. LaHusen, Dianne L. Brien, and Matthew Logan. "Deciphering Landslide Behavior Using Large-scale Flume Experiments."In Proceedings of the First World Landslide Forum. The irF st World Landslide Forum. Tokyo, Japan. November 18-21, 2008. Rights Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The onc tent of this document is not copyrighted. Authors Mark E. Reid, Richard M. Iverson, Neal R. Iverson, Richard G. LaHusen, Dianne L. Brien, and Matthew Logan This conference proceeding is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ge_at_conf/3 Mark E. Reid Deciphering Landslide Behavior Using Large-scale Flume Experiments Mark E. Reid (U.S. Geological Survey) ・ Richard M. Iverson (U.S. Geological Survey) ・ Neal R. Iverson (Iowa State University, USA) ・ Richard G. LaHusen (U.S. Geological Survey) ・ Dianne L. Brien (U.S. Geological Survey) ・ Matthew Logan (U.S. Geological Survey) Abstract. Landslides can be triggered by a variety of us to create landslides similar to small natural failures, but hydrologic events and they can exhibit a wide range of without the scale limitations of typical laboratory tests. movement dynamics. Effective prediction requires Our experiments focused on deciphering the influences of understanding these diverse behaviors. Precise evaluation in various hydrologic triggers and differing initial soil porosities the field is difficult; as an alternative we performed a series of on failure style, timing, and subsequent landslide acceleration. landslide initiation experiments in the large-scale, USGS We examined three hydrologic conditions that can initiate debris-flow flume. We systematically investigated the effects landslide movement, including: groundwater exfiltration into of three different hydrologic triggering mechanisms, soil from bedrock, prolonged rainfall infiltration, and bursts including groundwater exfiltration from bedrock, prolonged of intense rainfall (Reid et al. 1997). We also systematically rainfall infiltration, and intense bursts of rain. We also investigated the effects of initial soil porosity (n) on landslide examined the effects of initial soil porosity (loose or dense) dynamics at a field scale. A well-established maxim of soil relative to the soil’s critical-state porosity. Results show that mechanics holds that failure behavior during shear depends all three hydrologic mechanisms can instigate landsliding, but on the initial soil porosity (or void ratio) relative to a specific water pathways, sensor response patterns, and times to failure critical-state porosity (Schofield and Wroth 1968). Saturated differ. Initial soil porosity has a profound influence on soils looser than critical state contract as they shear, thereby landslide movement behavior. Experiments using loose soil elevating pore pressures and inducing rapid flow. Soils denser show rapid soil contraction during failure, with elevated pore than critical state dilate as they shear, temporarily reducing pressures liquefying the sediment and creating fast-moving pore pressures and retarding motion. debris flows. In contrast, dense soil dilated upon shearing, Here, we briefly describe some of our landslide initiation resulting in slow, gradual, and episodic motion. These experiments, document the effects of different hydrologic results have fundamental implications for forecasting triggers, and illustrate landslide behavior derived from landslide behavior and developing effective warning systems. different initial soil porosities. We conclude by discussing some implications of these results for predicting landslide Keywords. Landslide, experiment, failure behavior, behavior and developing effective warning systems. hydrologic trigger, critical state, porosity 1. Introduction Some landslides accelerate catastrophically with potentially lethal consequences, whereas others creep intermittently downslope, perhaps causing property damage but rarely fatalities. Rainfall patterns that initiate slide motion vary as well. Some slides require prolonged rainfall to instigate motion, yet others occur following short, intense rain bursts. Such profound differences in behavior have fundamental implications for designing mitigation strategies, implementing effective warning systems, and reducing risk. Precise evaluation of the causes of diverse landslide behavior is difficult because controlling effects cannot be isolated in the field; this limits our understanding of landslide dynamics as well as our prediction capabilities. Previous Fig. 1 Schematic longitudinal cross section of landslide studies have attempted to induce failure on natural hillslopes, experiments at the USGS debris-flow flume. The with varying degrees of success (Harp et al. 1990; Cooper et magnified ellipse depicts the positioning of sensors in al. 1998; Ochiai et al. 2004). Other studies have relied on vertical nests (from Iverson, et al. 2000). small-scale laboratory tests or experiments to infer landslide behavior (Eckersley 1990; Wang and Sassa 2001; Okura et al. 2. Experiment Configurations 2002; Take et al. 2004). In each of six experiments, we induced failure in a 0.65m As an alternative to field investigations and small-scale thick, 2m wide, 6m3 prism of loamy sand placed behind a experiments, we used the U.S. Geological Survey (USGS) rigid retaining wall on the 31˚ flume bed (Fig. 1). We debris-flow flume in Oregon, USA to perform controlled, systematically investigated hydrologic triggering of sliding by large-scale landslide initiation experiments. This flume allows either injecting water from channels in the bed (to simulate - 497501 - The First World Landslide Forum, 2008, Tokyo groundwater exfiltration), by overhead sprinkling (to simulate through the soil prism to daylight near the retaining wall (Fig prolonged or intense rainfall), or a combination of these 2A). Failure often occurred with large parts of the soil methods. We investigated differences in the failure behavior partially saturated. In contrast, experiments with dense soil of dense and loose soils (relative to critical state) by varying typically produced slip surfaces that nucleated within the soil initial soil porosity. To create loose soil, we dumped and prism, not along the bed, when positive pore pressures were raked the loamy sand without further disturbance. To create measured throughout the soil (Figure 2B).
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