Generally, landslide slope stability is analyzed using the Fellenius method based on the limited equilibrium method. For the purpose of deriving a more strict solution, the Bishop, Janbu, Spencer and the Morgenstern-Price methods are available. On the other hand, as computer technology has been developed, slope stability has been often analyzed using Finite Element Method (FEM). This method is characterized by the grasp of slope deformation, internal stress, local failure and so on.
By the way, Rigid Body Spring Method (RBSM) also has the same characters as FEM. This method easily deals with the failure of solids due to slippage and tensile cracking. Hence this method is suitable for the analysis of landslide stability.
Now, as is generally known, pore water pressure of the ground is an indispensable factor in analyzing slope stability. Overall safety factor is important to design a countermeasure and to estimate the stability of landslide slopes.
Accordingly to this paper, the method of analysis concerning pore water pressure and the method of deriving the overall safety factor using RBSM are proposed. Finally with a view of examining the propriety of the analysis method concerning pore water pressure using RBSM, and comparing the overall safety factor using limited equilibrium method, the proposal method is described with numerical examples of landslide slopes.

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In order to investigate the influence of some important factors at rainfall on the behaviour of pore water pressure in slope, the finite element analyses using saturated-unsaturated seepage were performed on the model slopes of four types soil layers with any given conditions of rainfall and groundwater inflow. The obtained effects of rainfall and groundwater seepage on the behaviour of pour water pressure in four different types of slopes are discussed by a detailed look at the different types of soil profile, the variation of vector due to rainfall and inflow to the reference section in the slope, and the variation of pore water pressure with elapsed time.

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In order to establish a evaluation method of shear deformation and failure of slope by AE parameter, largescale direct shear tests and rainfall-triggered slope failure experiments were carried out, and analysed the relation between stress-strain and AE parameters in the soil mass in these tests and experiments.
As the results, linear relation between shear work ratio and AE energy rate in the soil mass is made clear. In the direct shear test (strain-controlled), as the stress becomes larger, shear work ratio also becomes larger. In the slope failure experiment, stress state is almost constant and shear deformation proceeds with the saturation ratio rising, and shear work ratio becomes larger. These two types of soil mass deformation can be estimated by the shear work, so AE energy ratio also can estimate the shear deformation.
And in slope failure experiment, linear relation between shear strain rate and AE event rate in the soil mass is also made clear. These AE parameters are thought to be able to use in the Fukuzono's equation etc. instead of strain rate, and to estimate the failure time of the slope.

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In this paper the authors discuss not only a prediction method but a risk evaluation method for landslide occurrence by applying the vegetation index which is calculated from LANDSAT/TM data. We have examined the variation of vegetation index between the years of 1986 and 1989. The result shows the validity of this prediction method. The risk evaluation has been accomplished by using the Hayashi's quantification analysis of classes II and III in the following cases: (1) not applying the vegetation index, (2) applying the variation of the vegetation index and (3) applying the vegetation index. Finally, we have reached such conclusion that the result in case (3) has been appropriate to the risk evaluation for landslide occurrence.

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The effects of five typical slope stabilization techniques are investigated by considering the influences of strength constants c′ and φ′ on the safety factor of slopes. It is emphasized that such consideration is very important in the design of those countermeasures.

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In June 1994, an earth slope failure of considerable size, generally different in nature from normally encountered failures, occurred at a dam construction site in Yamanashi Prefecture. From the result of the post failure site investigation and various analysis, it was discovered that this failure was due to chemical weathering action on the original top layer of loam which strongly deteriorated the quality of its clay minerals. This phenomenon poses a challenging job for requirement of intensive geological survey studies to be conducted prior to commencement of dam construction in future.

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Field shear strengths (average shear strength along the slip surface) and shear strength parameters of the materials from the slip surfaces were evaluated for the landslide occurring in the Shimajiri mudstone area of Okinawa based on the stability analysis method in which the residual factor was incorporated. The type of the slides is classified into the fractured-mudstone slide, the softened-mudstone slide and the colluvial deposits slide. A back-analysis of these landslides showed that feild shear strengths are greater than residual strengths but smaller than peak strengths. The design strength parameters for control works were calculated by the proposed method and also by the graphic solution based on the back-analysis and shear strength parameters of landslide materials.

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