The effects of geological factors such as uneven topography and geological structures on the configuration and scale of landslides are discussed by use of case study for several active landslides. It is then shown that the length (L), depth (D) and width (W) of landslides have the following relationship: L/W=0.5-2.9, L/D=2.8-19.2, W/D=3.0-10.7
This suggests that the configuration and scale of landslides are greatly influenced by uneven surface, geological structures and heterogeneous strength of soils. In fact, the maximum scale of landslides increases with decreasing slope angle. Consequently, it is rare to have larger scale landslides in steep slopes. This is thought to be due to that a thick layer of unstable soils, which is necessary for a larger scale landslide, is unexpected to be remained for a long period of time as small collapse is frequently cased in such slopes.

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This paper deals with the index for risk evaluation of landslides, focusing on surface displacement at main scarp to collapse. Rainfall experiments indicate the existence of critical cumulative displacement at which a slope starts to collapse rapidly after the creep movement. A statistical analysis of various field and experimental data show that the critical cumulative displacement is in proportion with the length of the source area, and the ratio of critical cumulative displacement to the length of the source area (critical strain) ranges approximately from 0.006 to 0.02. Then an index of four-stage evaluation on the basis of the above range is proposed: precursor stage (<0.003), warning stage (0.003-0.006), failure stage (0006-0.02), and perfect failure stage (>0.02). Finally the wide validity of the proposal is verified by applying to several active landslides and old landslides.

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The behavior characteristics of flexible piles in landslides are simulated with a three-dimensional elasto-plastic finite element model where the sliding layer is incrementally driven by prescribed uniform boundary displacements. For many landslides, some part of the movement of sliding layer is not included in the observed value because measurements are started after the move-ment occurred. This partial movement is produced by antecedent boundary displacements. The influences of the shear strength of the sliding surface, antecedent boundary displacements, and pile spacing, Poisson's ration and the dilatancy of the sliding layer on the pile behavior characteristics are analyzed. The numerical comparisons show that the pile spacing and the shear strength of the sliding surface have significantly influences on the profile of the bending moment and shear force of the piles in landslides. The conventional design method based on the subgrade reaction solution gives smaller deflection of pile head and the bending moment of piles, and then make the piles in some dangerous side. The calculated pressure on the piles concentrates around the sliding surface, and this is similar to the assumption used in the conventional design method. Poisson's ratio and the dilatancy of the sliding layer have not significantly influence on the pile behaviors.

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A new slope stability analysis method based on FEM (SS-Method) is presented. Here normal and shear stresses acting on the middle point ‘A’ of an arc of a slip surface within an individual element were calculated by employing the Shape-Matrix technique. In order to evaluate the accuracy of the SS-Method, a “standard slope”, which was assigned a safety factor of unity on the critical slip surface, was utilized. The safety factor of the critical slip surface obtained from the SS-Method was 1.01, verifying the reliability of this method.
Safety factors for three test slopes calculated using the SS-method fell within valves obtained from other popular slope stability analysis methods.
Two slope failures occurred in a cut soft-rock slope under a road bridge foundation. One of which was analyzed with a new approach, where slope stability was estimated by combining both the SS-Method (safety factor on critical slip surface) and FEM-stress method (local safety factor). The failure mechanism is explained as follows: The foundation caused a concentration of stresses near its toe, and subsequently a shearing deformation occurred in the slope due to deterioration of strength after several rainfalls. The slope failures were finally triggered due to a heavy rainfall.
Countermeasures of the slope are also discussed by employing the FEM-stress method. Construction of an anchored framework or a simple frame-work are suggested.

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There are reported many serious disasters associated with water waves due to landslides suddenly inflowing into a reservoir and a bay. The estimation of water waves property has been carried out through the calculation of finite defferential method. This paper discusses the numerical procedure of finite element method to predict the water waves generated by landslides, and presents the numerical procedure simply combined with the balancing tensor diffusivity term into the finite element method in order to stabilize the numerical calculation. The results of the previous model experiments are compared with the properiety of the present method.

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Pit excavation survey for marsh deposits burying landslide depression was carried out to clarify formative age of the Nakanosawa landslide located in Mts. Shirakami, Northeastern Japan, from a view point of evolution of mountain slopes since Late Pleistocene. The deposits of two metres in thickness consisiting of peat, fallen timbers and volcanic ashes were excavated. They overlaydebris deposited by a landslide at the bottom. Wooden fragments collected from just above the landslide deposits are date back to 7.6ka to 8.1ka by radiocarbon method. Presumed formative age of Nakanosawa landslide is early Holocene as late as 8ka, because soil layer covering the debris deposits has not developed.

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