Studies on Three-Dimensional Stability Analysis Procedure in which the Residual Factor is Incorporated

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Strength measurement tests were carried out on landslide soils which showed a considerable variation in physical and mineralogical properties in order to obtain the their strength parameters c and φ for stability analysis. Then the three-dimensional stability analysis procedure, in which the residual factor was incorporated, was examined and proposed.The peak strength zone for strongly weathered and fractured mudstones was given by drawing the small area that reaches from the strength of c = 37.5kN/m_2 and φ = 35.0° close to the normally-consolidated strength in the c -φ figure. The parameters of normally-consolidated strength and residual strength were within the range of φ = 23 〜 30° and φ = 9 〜 17°, respectively. A fall in the strength from the peak to the residual state was clearly observed for the soil containing a large amount of silt and sand particles, and clay fraction below 20%. The variation of the strength reduction versus total contents of preferred-oriented clay minerals was expressed as a convex curve. Stress-displacement curves of landslide soils were classified into 4 types based on the total amount of minerals in soil.In the proposed analysis procedure, the average shear strength parameter acting along the slip surface was calculated precisely and was verified to be smaller than the parameter calculated by the two-dimensional analysis, and then each domain of both the peak and residual strengths mobilized at the slide could be expressed clearly on the whole slip surface area. This procedure will be helpful in rational and effective control works for landslide.