There are two types of debris flows, known as Lahar and Jökulhlaup. The word Lahar is Indonesian in origin and has to do with flows that are related to volcanic activity. A variety of factors may trigger a lahar, including melting of glacial ice due to volcanic activity, intense rainfall on loose pyroclastic material, or the outbursting of a lake that was previously dammed by pyroclastic or glacial material.

What is debris flow

An analytical method for developing a theoretical load-settlement curve for axially loaded piles in clay is presented. The method is based on the correlation of the ratio of load transfer to soil shear strength as a function of pile movement. The results of studies of field tests of instrumented piles and laboratory tests of small piles in clay are used to obtain the desired correlation. The correlation is presented in the form of a family of curves that are obtained when the ratios of load transfer to soil shear strength versus pile movement are plotted as a function of depth. The validity of the family of correlation curves is checked by comparing computed and actual load-settlement curves for some typical field tests. Results obtained by this method indicate that the method may be used effectively to determine load-carrying capacity for axially loaded piles in clay.

Closure to “Load Transfer for Axially Loaded Piles in Clay”

[1] Various methods have been proposed in the literature to predict the rainfall conditions that are likely to trigger landslides in a given area. Most of these methods, however, only consider the rainfall events that resulted in landslides and provide deterministic thresholds with a single possible output (landslide or no-landslide) for a given input (rainfall conditions). Such a deterministic view is not always suited to landslides. Slope stability, in fact, is not ruled by rainfall alone and failure conditions are commonly achieved with a combination of numerous relevant factors. When different outputs (landslide or no-landslide) can be obtained for the same input a probabilistic approach is preferable. In this work we propose a new method for evaluating rainfall thresholds based on Bayesian probability. The method is simple, statistically rigorous, and returns a value of landslide probability (from 0 to 1) for each combination of the selected rainfall variables. The proposed approach was applied to the Emilia-Romagna Region of Italy taking advantage of the historical landslide archive, which includes more than 4000 events for which the date of occurrence is known with daily accuracy. The results show that landsliding in the study area is strongly related to rainfall event parameters (duration, intensity, total rainfall) while antecedent rainfall seems to be less important. The distribution of landslide probability in the rainfall duration-intensity shows an abrupt increase at certain duration-intensity values which indicates a radical change of state of the system and suggests the existence of a real physical threshold.

Probabilistic rainfall thresholds for landslide occurrence using a Bayesian approach

Preface Chapter 1 What is debris flow? Various sediment moving phenomena Definition of debris flow Classification and characteristics of debris flows Stony type debris flow Turbulent muddy type debris flow Viscous debris flow The significance of the mechanical classification of debris flows Classifications on the other points of view Chapter 2 Models for mechanics of flow 2.1 Models for solids and fluid mixture as the multi-phase flow 2.2 Single-phase continuum models 2.2.1 Visco-plastic fluid model 2.2.2 Dilatant fluid model 2.3 Two-phase continuum models (Mixture theory) 2.3.1 Stress equilibrium equations 2.3.2 Coulomb mixture theory (Quasi-static debris flows) 2.4 Theory for subaerial rapid granular flows 2.4.1 Particle collision stress 2.4.2 Kinetic stress 2.4.3 Skeletal stresses 2.4.4 Constitutive relations 2.4.5 Application of the theory to dry granular flow 2.4.6 Comparison with other constitutive relations for inertial range 2.5 Role of interstitial fluid in inertial debris flows 2.6 The mechanism of immature and turbulent muddy debris flows 2.6.1 Immature debris flow 2.6.2 Turbulent muddy debris flow 2.7 Generalized theory for inertial debris flows 2.7.1 Theoretical considerations 2.7.2 Verification by experimental data 2.7.3 Approximate solution for solids concentration and resistance to flow 2.8 Newtonian fluid model for viscous debris flow 2.8.1 Theoretical considerations 2.8.2 Verification by experiments Chapter 3 Initiation and development of debris flow Initiation and development of debris flow due to gully bed erosion The formation of incipient debris flow by the effects of surface water runoff The development of stony debris flow on sediment bed Verification of the theory by experiments Landslide-induced debris flow Model for the transformation into debris flow Mathematical model for the one-dimensional motion of an earth block Numerical simulation of earth block and debris flow motions across three-dimensional terrain Debris flow and flood flow induced by collapse of natural dam Formative conditions and shapes of natural dam Failure in entire channel width and the resulting debris flow Prediction of debris flow/flood flow induced by the overflow in partial width Chapter 4 Characteristics of fully developed flow Translation of debris flow surge and the shape of the snout The case of stony type debris flow The case of viscous type debris flow Boulder accumulation at the forefront of stony debris flow Various concepts for the mechanism The theory of Takahashi (1980) Competence to transport large boulders The cause of intermittency Debris flow around bend Routing of debris flow in the transferring reach Kinematic wave method Dynamic wave method Chapter 5 Processes and geomorphology of deposition One-dimensional stoppage/depositing processes of stony debris flow The arrival distance at the abrupt change in channel slope Topography of deposit formed at an abrupt slope change Numerical simulation of depositing process One-dimensional depositing process of turbulent muddy debris flow Formation of debris flow fan Description of the experimental results for stony debris flow and empirical presentations of the feature of debris flow fan Numerical simulation of fan formation process and its verification Numerical simulation of fan formation by turbulent debris flow Particle size distribution in the fan formed by stony debris flow General situations found in the field and experimental data Mathematical model for particle size distributions Erosion and deformation of debris flow fan Experiments for the process of erosion Model and its verification for the fan comprised of uniform material Model and its verification for the fan comprised of heterogeneous material Chapter 6 Debris flow disasters and their reproduction by computer simulations The rain storm disasters at Okuetsu Outline of the disaster The natural dam formation and the damages done by backwater Processes of destruction of the natural dam and damages downstream Horadani debris flow disasters Outline of the disaster Hydrograph estimation of the debris flow Reproduction of debris flow depositing area on the fan Collapse of the tailings dam at Stava, Northern Italy Outline of the disasters Reproduction of the debris flow in the Stava River and its verification Disasters caused by the eruption of Nevado del Ruiz Volcano Outline of the disasters Reproduction of the phenomena Sediment disasters in Venezuela Outline of the disasters Debris flow routing under an arbitrary rainfall condition Reproduction of debris flow hydrograph and others in the Camuri Grande River Reproduction of sediment flooding on the Camuri Grande fan Debris flow disasters at Atsumari, Hougawachi, Minamata City Outline of the disasters Reproduction of the processes of debris flow Chapter 7 Countermeasures for debris flow disasters Methods to prevent from debris flow generation Hillside works Drainage works Groundsill and bed girdle Debris flow control by closed type check dam Sediment depositing process behind check (sabo) dam Erosion process of the deposit behind sabo dam Effects of sediment control by sabo dam to downstream Debris flow control by open-type sabo dams Kinds and sediment checking mechanism of open-type sabo dams Blocking model of grid-type dam Model for debris flow controlling by grid-type dabo dam Determination of the optimum spacing and the optimum position to install Making debris flow harmless by channel works and training walls Design of countermeasures on the fan of the Camuri Grande River Management of debris flow by training dike Design debris flows for the countermeasure planning Method based on the previous data Prediction of total sediment runoff by field investigation Theoretical prediction of debris flow scale Debris flow prone ravines and hazardous area Debris flow prone ravine Hazardous zone by debris flow Prediction of debris flow occurrence by rainfall References Notations Index

Debris flow : mechanics, prediction and countermeasures

This paper investigates rainfall-induced landslides on partially saturated soil slopes using the 2011 Umyeonsan landslides at the center of Seoul, Korea. An integrated analysis of rainfall-induced landslide was carried out through laboratory tests, field tests, and numerical analysis. The results of comprehensive investigations in the Umyeonsan region demonstrate that landslide activity is closely related primarily to rainfall and soil properties and slope geometry, and vegetation. Numerical analysis was also performed to confirm the effect of these factors on landslide occurrence. Special attention was given to rainfall penetration analysis to determine the wetting band depth for shallow and deep-seated slope failure in watershed-scale landslide. The simulated results agree closely with the investigation results, which indicates that the applied method is appropriate for use in the simulation of landslides in unsaturated soils.

/pdf/analysis-of-rainfall-induced-landslide-on-unsaturated-soil-2z1p4olkzh.pdf

Analysis of Rainfall-Induced Landslide on Unsaturated Soil Slopes

This study was conducted to determine the rainfall intensity-duration thresholds (ID curves) for landslide prediction by considering the effects of antecedent rainfall. Data for the time and location of landslides that occurred in South Korea from 1999 to 2016 were collected. Overall, 231 landslide histories from 1999 to 2013 were used to determine the rainfall thresholds, and 12 landslide histories from 2014 to 2016 were used to verify the proposed rainfall thresholds. Probabilistic ID curves were proposed to reflect the influence of other factors except rainfall, and ID curves for various inter-event time definitions (IETDs) were suggested to analyze the variation in the ID curves with the effects of antecedent rainfall. The results suggest that the IETD indicates the duration for which the antecedent rainfall affects the ground condition. It was also found that the ID curve for 12 h of the IETD was the most reliable of the verification procedures using the receiver operating characteristic (ROC) plot and threat score (TS).

Rainfall intensity-duration thresholds for landslide prediction in South Korea by considering the effects of antecedent rainfall

Landslides are mainly triggered by decrease in the matric suction with deepening the wetting band by rainfall infiltrations. This paper reports rainfall-induced landslides in partially saturated soil slopes through a field study. A comprehensive analysis on Umyeonsan (Mt.) landslides in 2011 was highlighted. The incident involves the collapse of unsaturated soil slopes under extreme-rainfall event. Fundamental studies on the mechanism and the cause of landslides were carried out. A number of technical findings are of interest, including the failure mechanism of a depth of soil and effect of groundwater flow, the downward movement of wetting band and the increase of groundwater level. Based on this, an integrated analysis methodology for a rainfall-induced landslide is proposed in this paper that incorporates the field matric suction for obtaining hydraulic parameters of unsaturated soil. The field matric suction is shown to govern the rate of change in the water infiltration for the landslide analysis with respect to an antecedent rainfall. Special attention was given to a one-dimensional infiltration model to determine the wetting band depth in the absence of the field matric suction. The results indicate that landslide activities were primarily dependent on rainfall infiltration, soil properties, slope geometries, vegetation, and groundwater table positions. The proposed methodology has clearly demonstrated both shallow and deep-seated landslides and shows good agreement with the results of landslide investigations.

/pdf/rainfall-induced-landslides-by-deficit-field-matric-suction-1aqp27le64.pdf

Rainfall-induced landslides by deficit field matric suction in unsaturated soil slopes

This study describes a combined method for rainfall-induced debris flow initiations (landslides) and propagations including a series of numerical analyses. In this study, the debris is assumed as a mixture of soils and water which is physically non-Newtonian fluid. The emphasis is placed on applying the effect of the combination of rainfall-induced landslides and debris flows to the numerical analysis. An analysis of rainfall-induced landslides is conducted to identify the thickness and location of the initial volume of debris flow. The movement of debris flow is subsequently simulated considering entrainments affected by the initial wetting condition (wetting front) estimated from the rainfall-infiltration analysis. The proposed method can simulate a sequential process from the initiation of the debris flows to the deposition based on the prediction of slope failure by rainfall, fluid dynamics based on Navier–Stokes equation, and the analysis of entrainments by considering the effect of the weight of debris and the wetting condition of soil beds. Based on the numerical results of this study, the proposed method could be applied to the analysis of regional-scale landslides and debris flows.

A combined method for modeling the triggering and propagation of debris flows

This study was conducted to estimate the susceptibility of landslides on a test site in Malaysia (Hulu Kelang area). A Geographic Information system (GIS)-based physical model named YS-Slope, which integrates a mechanistic infinite slope stability method and the geo-hydrological model was applied to calculate the safety factor of the test site. Input data, slopes, soil-depth, elevations, soil properties and plant covers were constructed as GIS datasets. The factor of safety of shallow landslides along the wetting front and deep-seated landslides at the bottom of the groundwater were estimated to compare with the analysis results of the existing model and actual landslides in 2008. According to the results of the study, shallow landslides mainly occurred in the central area which has many historical landslides, while deep-seated landslides were predominant in the east side of the study area. A ROC analysis was conducted and it is shown that the prediction result at the end of the northeast monsoon for shallow landslides showed relatively high accuracy compared with other predictions.

Susceptibility Assessments of Landslides in Hulu Kelang Area Using a Geographic Information System-Based Prediction Model

This study was conducted to suggest a landslide triggering rainfall threshold (ID curve) for landslide prediction by considering the effect of antecedent rainfall. 202 rainfall data including domestic landslide and rainfall records were used in this study. In order to consider the effect of antecedent rainfall, rainfall data were analyzed by changing Inter Event Time Definition (IETD) and IETD based ID curve were presented by regression analysis. Compared to the findings of the previous studies, the presented ID curve has a tendency to predict the landslides occurring at a relatively low rainfall intensity. It is shown that the proposed ID curve is appropriate and realistic for predicting landslides through the validation of proposed ID curve using records of landslides in 2014. Based on this analysis, it is found that the longer IETD, the greater the effect of antecedent rainfall, and the steeper the gradient of ID curve. It is also found that the rainfall threshold (intensity) is higher for the short period rainfall and lower for the long period rainfall.

http://koreascience.or.kr:80/article/JAKO201614139533706.pdf

Moonhyun Hong

Papers

Rainfall intensity-duration thresholds for landslide prediction in South Korea by considering the effects of antecedent rainfall

Rainfall-induced landslides by deficit field matric suction in unsaturated soil slopes

A combined method for modeling the triggering and propagation of debris flows

Susceptibility Assessments of Landslides in Hulu Kelang Area Using a Geographic Information System-Based Prediction Model

Rainfall Threshold (ID curve) for Landslide Initiation and Prediction Considering Antecedent Rainfall