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Kim, Sukwoo,Kim, Minseok,An, Hyunuk,Chun, Kunwoo,Oh, Hyun-Joo,Onda, Yuichi Elsevier 2019 Catena Vol.182 No.-
<P><B>Abstract</B></P> <P>High resolution DEMs and physical soil strength, among other factors, have significant effects on the shallow landslide instability mapping. Subsurface flow in soil mantle normally is assumed by slope parallel flow based on resolution of DEMs and, measuring soil strength, which is affected by subsurface flow within the soil mantle, is difficult in both the field and the laboratory. Thus, the aims of this study are to investigate the effect of subsurface flow by high resolution Lidar DEMs and the effect of physical soil strength attributes on shallow landslide instability mapping, respectively. In this study, two DEMs (with 1 m and 5 m resolutions) were used and, physical soil strength was calibrated using a simple subsurface hydrological concept with LiDAR and field survey data in order to quantify the influence of soil strength on shallow landslide instability mapping. To this end, various field surveys were performed at Woomyeon Mountain, Seoul, Republic of Korea, where shallow landslides occurred in 2012. The physical shallow landslide stability (SHALSTAB) model were applied. The modified success rate (MSR) method were applied to assess the predicted results. In the first series of simulations, using the two DEMs and experimentally derived soil strength values, relatively low MSR values of 0.42–0.468 for the 1 m DEM and 0.42–0.47 for the 5 m DEM were recorded. In the second series of simulations, using soil strength calibrated using a simple theoretical approach, the MSR for the 1 m DEM was 0.78–0.823 and the MSR for the 5 m DEM was 0.723–0.80. These results indicated that soil strength had a more important role in shallow landslide instability mapping than assuming subsurface flow by topographic resolution. Therefore, it may be useful to apply field-collected soil strength data using hydrological concepts to improve the accuracy of predictive models based on high-resolution surface data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 1 m resolution DEM and 5 m resolution DEM conducted from Lidar were used. </LI> <LI> The soil strength values were calculated using a simple hydrologic concept with field survey data and Lidar. </LI> <LI> Shallow landslide instability were affected by soil strength than high resolution DEMs. </LI> </UL> </P>
The Slope Failure by Upward Seepage Flow in a Gradual Slope: Case Study in Sandy Slope Experiments
( Min Seok Kim ),( Young-suk Song ),( Hyun-joo Oh ),( Kyeong-su Kim ),( Choon-oh Lee ),( Sueng Won Jung ),( Yuichi Onda ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
Slope failures are commonly occurred in steep hillslopes (>30 degrees) due to subsurface flow mechanism in soil mantle during unexpected rainfall intensity-duration. However, there were some slope failures by upward subsurface flow related with piping flow, detected at gradual hillslope (< 30 degrees) monitored under granite area, Icheon-city, Korea. The expansion of slope failure by the effect of subsurface flow were monitored at specific gradual hillslope site during 2004-2017 years. We proved its mechanism using a flume experiments with an artificial rainfall. In natural site, particularly for those slope failure which occur under intense rainfall is that from the failure surface to bedrock is saturated and has positive pore-water pressures from bedrock acting on it. In a lab test for 5 times, we observed slope failure initiation and its expansion under upward seepage direction and force (i.e. hydraulic gradient) in saturated state of soil. These subsurface flow by the seepage direction and force maybe play important role in slope failure mechanism in soil mantle of gradual slope in a granite study site.