• Journal of the Korean Geotechnical Society
• /
• v.29 no.1
• /
• pp.23-27
• /
• 2013

The risks of debris flows caused by climate change have increased significantly around the world. Recently, landslide disaster prevention technology is more focused on the failure and post-failure dynamics to mitigate the hazards in flow-prone area. In particular, we should define the soil strength and flow characteristics to estimate the debris flow mobility in the mountainous regions in Korea. To do so, we selected known ancient landslides area: Inje, Pohang and Sangju debris flows. Firstly we measured physical and mechanical properties: liquidity index and undrained shear strength by fall cone penetrometer. From the test results, we found that there is a possible relationship between liquidity index and undrained shear strength, $C_{ur}=(1.2/I_L)^{3.3}$, in the selected areas, even though they were different in geological compositions. Assuming that the yield stress is equal to the undrained shear strength at the initiation of sliding, we examined the flow characteristics of weathered soils in Korea. When liquidity index is given as 1, 1.5 and 3.0, the debris flow motion of weathered soils is compared with that of mud-rich sediments, which are known as low-activity clays. At $I_L=1$, it seems that debris flow could reach approximately 250m after 5 minutes. As liquidity index increased from 1 to 3, the debris flow propagation of weathered soils is twice than that of low-activity clays. It may be due to the fact that soil masses mixed with the ambient water and then highly fragmented during flow, thereby leading to the high mobility. The results may help to predict the debris flow propagation and to develop disaster prevention technology at similar geological settings, especially for the weathered soils, in Korea.

• Journal of the Korean Geotechnical Society
• /
• v.38 no.4
• /
• pp.5-20
• /
• 2022

To analyze the flow and density variations in debris flows, a two-phase finite volume model simplified with momentum equations was constructed in this study. The Hershel-Buckley rheology model was employed in this model to account for the internal and basal friction of debris flows and was utilized to analyze complex topography and entrainments of basal soil beds. In order to numerically solve the debris flow analysis model, a finite volume model with the Harten-Lax-van Leer-Contact method was used to solve the conservation equation for the debris flow interface. Case studies of circular dam failure, non-Newtonian fluid dam failure, and multiple debris flows were analyzed using the proposed model to evaluate shock absorption capacity, numerical isotropy, model accuracy, and mass conservation. The numerical stability and correctness of the debris flow analysis of this analysis model were proven by the analysis results. Additionally, the rate of debris flow with various rheological properties was systematically simulated, and the effect of debris flow rheological properties on behavior was analyzed.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.273-280
• /
• 2008

Debris flow has been considered as one of the major natural hazards and possesses tens to hundreds times higher destructive potential than that of slope failure. In the past 5 years, its occurrence frequency was and is likely to increasing due to the global warming. Although various methods such as basin vegetation or structural dams can be implemented to counter measure the debris flow, these methods are not always the right answer to the problem when magnitude of debris flow is far bigger than could be defended. Land use regulations to avoid the hazard or early debris flow warning system to evacuate the expected inundated area can be more economical and practical actions for those cases. In this study, an early debris flow warning system composed of rainfall measuring device, debris flow sensing device and video camera is introduced. The system is designed to issue the warning when rainfall threshold is exceeded or debris flow is sensed by sensing device. Developed monitoring system can be used to cope promptly with the debris flow risk.

• Ocean and Polar Research
• /
• v.24 no.3
• /
• pp.289-300
• /
• 2002

The Lago Sofia conglomerates encased in the Cretaceous Cerro Toro Formation, southern Chile, represent a gigantic submarine channel system developed along a foredeep trough. The channel system consists of several tributaries along the trough margin and a trunk channel along the trough axis. Voluminous debris flows were generated ubiquitously along the tract of the submarine channel mainly by the failure of nearby channel banks or slopes. The flows transformed immediately into multiphase flows and resulted in very thick-bedded mass-flow deposits with a peculiar structure sequence. The mass-flow deposits commonly overlie fluted or grooved surfaces and consist of a lower division of clast-supported and imbricated pebble-cobble conglomerate with common basal inverse grading, and an upper division of clast- to matrix-supported and disorganized pebble conglomerate or pebbly mudstone with abundant intraformational clasts. The structure sequence suggests a temporal succession of a turbidity current, a bipartite hyperconcentrapted flow with active clast collisions near the flow base, and a cohesive debris flow probably with a rigid plug. The multiphase flow is interpreted to have resulted from transformation of clast-rich but cohesive debris flows. Cohesive debris flows appear to transform more easily into dilute flow types in subaqueous environments because they are apt to hydroplane. This is in contrast to the flow transitions in subaerial environments where noncohesive debris flows are dominant and difficult to hydroplane.

• The Journal of Engineering Geology
• /
• v.28 no.3
• /
• pp.341-348
• /
• 2018

Landslides can be caused by localized intense rainfall. The loss of human lives and damage to property from landslides is increasing. However, little information exists on the movement and flow of sediment material at the time of rapid landslides. In this study, a field survey was conducted of landslides that occurred in 2013 in the Hadari area of Yeoju city in Korea. This was followed by numerical analysis. The purpose is to analyze the characteristics of a consequent debris flow and its movement at the time of failure. The results of the field survey and numerical analysis are consistent with each other. The maximum velocity of the debris flow was ~9.335 m/s and the maximum sediment thickness ~4.674 m. The latter is similar to the traces of debris flow observed in the field.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.1
• /
• pp.171-179
• /
• 2013

In recent years in Korea, Typhoon Rusa (2002), Typhoon Maemi (2003), and the localized extreme rainfall followed by Typhoon Ewiniar in 2006 devastated residential areas, roads, and agricultural lands in Gangwon province where 90% of the area is in mountainous regions. Most of the economic losses and casualties were concentrated in the area near the mountain valleys and creeks due to the floods and debris flows. In this study, DATABASE, which includes a total 180 debris flow events in the Gangwon area, was created by collecting the hazard records and field investigations of existing debris flow sites. Analysis results showed that the most of the debris flows in Gangwon province initiated from the small slope failure with relatively steep slope of $18.1^{\circ}$. And they flowed short distances about 420 m in gentle slope with the average angle of $18.1^{\circ}$. In addition, rainfall condition was important for the triggering of debris flow not only at the day of debris flow but also extended period of rainfall before debris flow.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.29 no.5
• /
• pp.535-541
• /
• 2011

A debris flow is caused by torrential rain in mountainous regions and carries mixture of fragmental matter from slope failure, deposit soils from a valley floor and a large amount of water. It seriously damages facilities, houses, and human lives in its path. We tried to apply debris flow behavior estimation model developed in foreign country to domestic case. The study area is Inje-county, Gangwon-do and aerial photos and GPS surveying were used to collect information of starting and end point of the landslide and debris flow. The analysis showed that L/H for forecasting the travel distances of debris flows has the mean of 4.93 and standard deviation of 0.98. This model tended to overestimate the scale and extent of debris flows. In Inje-county's case, a debris flow is caused by multiple simultaneous small-scale landslide. This is quite different from the foreign cases in which a large-scale landslide cause a large-scale debris flow. Thus, an empirical model suitable for domestic conditions needs to be developed.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.5C
• /
• pp.263-271
• /
• 2008

Investigation and analysis of the debris flow characteristics such as basin topography, geologic conditions of initiation location and triggering rainfall are required to systematically mitigate debris flow hazard. In this paper, 48 debris flows which had caused some damages to the highway in the past 5 years are investigated and their characteristics of basic topography and triggering rainfall are analyzed. Debris flows are found to occur in small basins having the area of $0.01{\sim}0.65km^2$ range and mostly initiated by the surficial failure of natural slope having the inclination of 29~55 degree during the intense rainfall. As for the triggering rainfall, rainfall of 2 to 5 year recurrence frequency are found to be able to trigger the debris flow and magnitude of debris flow in a basin could depend on the rainfall intensity and cumulative amount.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.09a
• /
• pp.1041-1050
• /
• 2009

Many slope failures and debris flows were occurred in Jinbu area of Gangwon Province due to heavy rainfall of much more than 400mm in July, 2006. In the area, although about 3 years passed, valleys and gulleys keep their original form when the events happened. Field investigations were performed on Singi-ri and Bongsan-ri in Jinbu area to examine the characteristics of debris flow as well as slope failure. As the result, debris flows were classified as 3 types according to their characteristics analyzed by field investigations.

• Nuclear Engineering and Technology
• /
• v.55 no.8
• /
• pp.3017-3029
• /
• 2023

In the late in-vessel phase of a nuclear reactor severe accident, the internal heat transfer and crust evolution during the debris bed melting process have important effects on the thermal load distribution along the vessel wall, and further affect the reactor pressure vessel (RPV) failure mode and the state of melt during leakage. This study coupled the phase change model and large eddy simulation to investigate the variations of the temperature, melt liquid fraction, crust and heat flux distributions during the debris bed melting process in the hypothetical severe accident of HPR1000. The results indicated that the heat flow towards the vessel wall and upper surface were similar at the beginning stage of debris melting, but the upward heat flow increased significantly as the development of the molten pool. The maximum heat flux towards the vessel wall reached 0.4 MW/m². The thickness of lower crust decreased as the debris melting. It was much thicker at the bottom region with the azimuthal angle below 20° and decreased rapidly at the azimuthal angle around 20-50°. The maximum and minimum thicknesses were 2 and 90 mm, respectively. By contrast, the distribution of upper crust was uniform and reached stable state much earlier than the lower crust, with the thickness of about 10 mm. Moreover, the sensitivity analysis of initial condition indicated that as the decrease of time interval from reactor scram to debris bed dried-out, the maximum debris temperature and melt fraction became larger, the lower crust thickness became thinner, but the upper crust had no significant change. The sensitivity analysis of in-vessel retention (IVR) strategies indicated that the passive and active external reactor vessel cooling (ERVC) had little effect on the internal heat transfer and crust evolution. In the case not considering the internal reactor vessel cooling (IRVC), the upper crust was not obvious.