A numerical method which achieves the coupled analysis of the Darcy flows in porous media and the Navier-Stokes flows in fluid domains is proposed, and it is applied to the computation of preferential flows in soils, such as a pipe-flow. The method uses the Darcy-Brinkman equations for the continuous modelling of the interfacial flow velocity, and applies the finite volume method to the spatial discretization and the fractional step method to the numerical simulation of the incompressible fluid. The coupling of the two different flows is realized by the relevant interpolation of the pressure and the flow velocity onto the interface at which permeability and porosity are discontinuous. The numerical simulation of a pipe flow created in a soil block has been conducted, and the results have revealed that the proposed method can simulate the transition to the Hagen-Poiseuille flow through the flow pipe and that the detailed description of the preferential flow in the fluid domain is enabled as well as the seepage flow field in the porous media.

抄録全体を表示

Hong Kong faces landslide risk every year where many landslides are triggered by heavy rainfalls during summer. The infiltration into the slope can adversely affect the stability of the slopes in different ways. The groundwater response in slope is one of the subjects of interest, and also a subject to be understood. Part of the challenge is the complex nature of the groundwater flow within the unsaturated soil above the groundwater table. This paper attempts to provide a better understanding of the subject by developing and testing a numerical model to study the response of groundwater when it experiences a severe rainstorm. The results of testing this model provide some insight on how rainstorm affects the groundwater inside the slope and some understanding on the mechanism by which a transient perched groundwater table is developed.

抄録全体を表示

In recent years, localized torrential rainfall caused by abnormal weather happens frequently. It triggered numerous sediment disasters as slope failure. During heavy rainfall, it is estimated that degree of saturation increases rapidly in the ground with water flow. It may cause pore air occluding with rapid water flow in some cases. Because natural slope is often unsaturated, it is required to consider effect of pore air pressure. In this study, coupled stress-flow analysis is performed by calculating two-phase flow considered effect of pore air pressure. Failure mechanisms of slope are examined by decreasing effective stress, which is induced by increases of pore water and air pressure. It is discussed on slope stability by the case studies focused land features and rainfall intensity under like these conditions. The calculation results could be divided two prominent failure types. One is resulted from decreasing effective stress caused by rise of ground water level under the condition of gentle slope. And another one is resulted from gravitational sliding caused by increasing soil mass weight with short-time heavy rainfall under the condition of steep slope.

抄録全体を表示

To investigate the phenomenon and infiltration behavior of non-orthogonal rainfall infiltration into the surfaces of unsaturated sand slopes, a series of model tests of unsaturated sand slopes under different rainfall intensity, slope angle, and void ratio were carried out with a self-designed artificial rainfall device. For the purpose of contrast with the test results, a large amount of the numerical simulations was also conducted using classic methods for treating normal component of rainfall as infiltration boundary condition. Comparisons of the results of numerical simulation and of the tests indicate that there are differences which show that the orthogonal infiltration condition is unsuitable for analysis of rainfall induced seepage in unsaturated slopes.

抄録全体を表示

In this study, the instability of rainfall-induced shallow landslides on Mt. Umyeonsan was examined by a coupled hydro-mechanical finite element (FE) model. Field and laboratory investigations were performed to explore mechanisms of shallow landslides and to determine the model parameters. The coupled hydro-mechanical FE model is shown to be capable of simulating the progressive failure of a slope within the soil layer. The slope failures occurred on the surficial layer-bedrock interface, which shows good agreement with the actual failure zone. Through comparisons with field investigations, the presented method reasonably identified the potential zone of landslide initiation as compared with a limit equilibrium method. Therefore, the coupled simulation allows both the hydraulic and mechanical behavior of slope to be considered and realistically modelled.

抄録全体を表示

The smoothed particle hydrodynamics SPH method, which is based on the mesh-free Lagrangian scheme, is commonly used to solve large deformation problems in geotechnical engineering. The method can be used to solve large deformation problems without distortion of the mesh. Moreover, it can handle the governing equations and constitutive models for geomaterials based on continuum mechanics. However, numerical inaccuracies are a problem with the conventional SPH method. In this paper, we reported an improved method, Symmetric SPH (SSPH). Validations of simulations of simple shear problems in elastic and elasto-plastic materials were carried out, and the SSPH method demonstrated significant improvements in numerical accuracy compared with the SPH method. Furthermore, excavation problems with loose to dense sand were analyzed to examine the applications of the SSPH method.

抄録全体を表示

The concern for climate change has increased worldwide. Localized rain storms with high intensity and short duration have been observed in Asia. South Korea is one of the countries that have also been impacted by extreme rainfall events during typhoons. Extreme rainstorms have caused major damage from landslides and debris flows in the South Korean mountains. Korea is also experiencing changes in climate parameters, including annual temperature and precipitation. In this research, a physically based slope stability model for shallow landslide is presented. A model for the prediction of both topographic and climatic control on shallow landslide initiation processes in hilly mountainous terrain is proposed. We applied two simple hydrological models, coupled with the infinite slope stability analysis, to the July 2011 landslide event in Yongin, South Korea. The rainfall predicted to cause instability in each topographic element is characterized by duration and frequency of occurrence. The results obtained from the QD-SLaM has been compared with those obtained by the steady-state model, SHALSTAB. A GIS-based landslide inventory map of 109 landslide locations was prepared using data from previous reports, aerial photographic interpretation, and extensive field work. And this inventory of landslide scars was used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions. This result demonstrate the QD-SLaM was successful in identifying the unstable areas under return critical rainfall than the SHALSTAB was.

抄録全体を表示