An energy based approach has been proposed to evaluate travel distance of failed slopes based on a theoretical model of a rigid block resting on a slope and model shake table tests. The energy approach is then applied in this paper to a number of slopes failed during the 2004 Niigataken-Chuetsu earthquake to back-calculate mobilized friction coefficients μ, revealing their strong dependency on initial slope inclinations. The μ-value was found to be smaller than the initial slope inclination for gentler slopes, indicating that the failed soil mass tends to accelerate. It tends to decrease with increasing volume of failed slope, which is consistent with previous case studies on huge landslides.

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We made structural analysis for the gravitational tilting structures of steeply dipping cleavages in the Upper Permian alternating beds of siliceous slate and tuffaceous slate, and revealed their geological factors and formative process. The gravitational tilting has occurred due to two distinctive movements; creep as shearing along cleavage planes and topple as rotation of completely separated blocks. During the gravitational tilting deformation, creep has preceded, and continuously creep and topple have occurred simultaneously. Cleavage fractures have been selectively formed in tuffaceous slate, while rarely in red siliceous slate. Abundant quartz veins exist in red siliceous slate perpendicular or oblique to cleavages. These quartz veins prevent shearing along cleavage planes in red siliceous slate as anchor, and prompt formations of cleavage fractures in tuffaceous slate.

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This paper discussed the shear strengths along the slip surface in the first-time activation and reactivation of Asato landslide, which is a quasi-first activated slide in the area of Shimajiri-mudstone, Okinawa, Japan and its stability analysis utilizing the shear strength characteristics. It is considered that in the reactivation, residual strength is applicable in most of the slip surface area, while the remaining part of it is at the fully softened strength. In the stability analysis during sliding subsequent to the first-time activation, using the residual strength as the average shear strength that acts along the slip surface for the entire slip surface enables estimation of the position of groundwater level. For the first-time activation, the average shear strength acting along the slip surface (c´, φ´) was calculated through the application of the estimated groundwater level. The parameters of c´=26.8kN/m², φ´=22.9° and the residual factor R=0.49 indicate that both the peak (fractured-mudstone) and the residual (structural weak planes) strength prevail in the slip surface area. The c´- tanφ´ diagrams of stability analysis, which are constructed for the first-time activation and reactivation of the landslide, are beneficial for the control works for landslide. These results can be valuable in the risk evaluation of the quasi-first activated slides.

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For realistic prediction and assessment of falling trajectories of rock mass using simulation of rock fall and rock mass failure, a modeling technique for the representation of geographical topography of slope, and shape and size of rock mass is required. A method of bonding a large number of particles has been relatively commonly used for modeling of rock fall in three-dimensional distinct element method. This study, however, suggests the application of polyhedron block for more realistic modeling of rock shape and size rather than the conventional method. In this paper, contact detection scheme“common-plane”supporting polyhedron block built in three-dimensional distinct element method, 3DEC, was considered to be effective for the simulation of rock fall and rock failure involved with revolutions and collision with a slope at high speed. Validity and applicability of the method to rock fall and rock failure simulation was then investigated. In addition, 3DEC code was applied to a slope where a road was at risk of rock fall and rock failure. It is shown that the results of simulation provided the process of rock fall as well as trajectories and kinetic energy necessary for the determination of engineering measures.

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In order to predict the occurrence of rainfall-induced landslide by monitoring (measurement) of surface displacement, simulation model of surface displacement of shallow slope due to rainfall has been already developed. In the model, a change of stress due to the change of matric suction is evaluated in a suction-induced bond stress. In this study, suction-induced bond stress is newly expressed by Karube's equation using Soil water characteristic curve (SWCC) derived easily by infiltration test of undisturbed sample. And it is applied to the simulation of the surface displacement due to middle-scale rainfalls at the granite slope in Hiroshima in order to show the applicability of the model for the simulation. It reveals that the improved model simulates observed surface displacement relatively well. And the larger the suction-induced bond stress correspond to some suction value, the greater the calculated shear strain of the soil layer. It causes the large surface displacement with large suction-induced bond stress.

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