Shuji Moriguchi

Landslide susceptibility analysis with logistic regression model based on FCM sampling strategy

Abstract Several mathematical models are used to predict the spatial distribution characteristics of landslides to mitigate damage caused by landslide disasters. Although some studies have achieved excellent results around the world, few studies take the inter-relationship of the selected points (training points) into account. In this paper, we present the Fuzzy c-means (FCM) algorithm as an optimal method for choosing the appropriate input landslide points as training data. Based on different combinations of the Fuzzy exponent ( m ) and the number of clusters ( c ), five groups of sampling points were derived from formal seed cells points and applied to analyze the landslide susceptibility in Mizunami City, Gifu Prefecture, Japan. A logistic regression model is applied to create the models of the relationships between landslide-conditioning factors and landslide occurrence. The pre-existing landslide bodies and the area under the relative operative characteristic (ROC) curve were used to evaluate the performance of all the models with different m and c . The results revealed that Model no. 4 ( m =1.9, c =4) and Model no. 5 ( m =1.9, c =5) have significantly high classification accuracies, i.e., 90.0%. Moreover, over 30% of the landslide bodies were grouped under the very high susceptibility zone. Otherwise, Model no. 4 and Model no. 5 had higher area under the ROC curve (AUC) values, which were 0.78 and 0.79, respectively. Therefore, Model no. 4 and Model no. 5 offer better model results for landslide susceptibility mapping. Maps derived from Model no. 4 and Model no. 5 would offer the local authorities crucial information for city planning and development.

Liquefaction induced lateral spread analysis using the CIP method

Abstract This paper presents a CIP (cubic interpolated pseudoparticle) based numerical method for liquefaction induced lateral spread analysis in the framework of fluid dynamics. Previously, the authors presented similar methods using a SIMPLE-VOF based commercial code but were not able to extend such a code to simulate lateral spread of liquefied ground with an overlaying non-liquefied layer, which is the most common and more practical post liquefaction problem. In this study, the CIP method is used because it is able to treat solid, liquid and gas together, can correctly define the flow behavior at interfaces of multi-fluids and can also be used as a unified scheme for both compressible and incompressible materials. A Bingham model that takes the undrained strength of soils into account is used as the basic constitutive model. A CIP based numerical scheme, which has been successfully used in fluid dynamics problems, is modified by incorporating the Bingham viscosity and an implicit calculation procedure for pressure terms. The Poisson equation is used to compute the pressure over the whole domain. The current numerical method is validated and good agreement is produced in comparison with experimental results. A previously verified similitude for liquefied ground flow is also reproduced by this method. The method is, finally, used to simulate shaking table tests on a liquefied subsoil model with an overlaying non-liquefied layer. From the results of simulations, the numerical method is found to satisfactorily reproduce the time histories of ground surface velocity and displacement and depth distribution of displacement.

Large Deformation Analysis for Costal Geo-Disasters Using Continuum and Discrete Modeling

Various kinds of geo-disasters have occurred, such as soil avalanches, landslides, failure of river dike, liquefaction and scoring. These disasters have caused serious damage to infrastructures and human activities. Numerical simulations are one of the powerful tools for predicting (1) when the failure will take place, (2) where the failure take place, (3) how far the collapsed soil mass will flow, and (4) how large the impact force to structures will be. In this paper, FEM, CFD, DEM and SPH are introduced as numerical methods for costal geodisasters. Brief explanation of theory of each numerical method will be described in this paper. Based on simulated results, advantages and disadvantages of different methods are discussed.

Performance of the SPH Method for Deformation Analyses of Geomaterials

Various types of behaviors of different soils have been predicted by using the finite element method (FEM) with comprehensive constitutive models developed in geomechanics. There are, however, still some problems for the large deformation analyses within the framework of FEM. Numerical instabilities arise due to the distortion of the FE mesh. In this work, deformation analyses of geomaterials using Smoothing Particle Hydrodynamics (SPH) method are carried out. The SPH method belongs to the class of particle methods. In this paper, the analytical accuracy and the stability of SPH method are investigated for deformation analyses of geomaterials which are assumed to be solid or fluid.

CIP-Based Numerical Simulation of Snow Avalanche

In order to predict a flow area of snow avalanche, a numerical method based on fluid dynamics has been proposed. In the CIP-based numerical method, snow is modeled as a Bingham fluid with the consideration of the Mohr-Coulomb failure criterion. Therefore, the cohesion c and the internal friction angle φ are the material parameters for the flowing medium. In this study, using the numerical method with THINC in CIP, the snow avalanche model tests were simulated. In the model tests, snow avalanches were reproduced in a low-temperature room. In the tests, snow flowed on a model slope and the travel length of snow was measured. The parameters used in the simulations are obtained from a previous research. In order to investigate the applicability of the numerical method proposed in this study, the results of model tests were compared with simulation results.

Numerical Prediction of Impact Force of Geomaterial Flow against Retaining Structure using CIP Method

This study presents numerical framework for predicting impact force of geomaterial flow against a retaining structure. The numerical scheme used in this study is CCUP method that is based on fluid dynamics. In order to describe behavior of geomaterials, the Mohr-Coulomb failure criterion is introduced into the Bingham plastic fluid model. To validate the numerical framework, a series of laboratory experiments related to impact force of geomaterial flow against a retaining structure were conducted, and then simulations of the experiments were carried out. In this paper, the numerical framework, the laboratory experiments and numerical simulations are explained, and effectiveness of the numerical framework is discussed.

CIP and CA Based Large Deformation Analysis of Collapse of a Soil Column

ABSTRACT This paper presents a numerical method for large deformation analysis of collapse of a soil column. The CA (Cellular Automata) method, which deals with the prediction of behavior of granular assemblage based on simple local rules, and the CIP (Cubic Interpolated Pseudoparticle) method, which treats solid, liquid and gas together in the framework of fluid dynamics, are used as numerical solvers. The CIP solver can correctly define the behavior at interfaces and can also be used as a unified scheme for both compressible and incompressible materials. In the simulations based on the CA method, two different particle sizes are used. On the other hand, for the CIP method a Bingham plastic model that takes the minimum undrained strength of soil into account is used as the basic constitutive model. Simulations results obtained from both methods are discussed.