Seiichi Gibo

Colloid-chemical and mineralogical differences of smectites taken from argillized layers, both from within and outside the slip surfaces in the Kamenose landslide

Abstract Colloid-chemical activity of three smectitic clays taken both from within and outside the slip surfaces in the Kamenose landslide was assessed in terms of the relative viscosity increment (RVI) and sediment volume (SV) of the clay sol saturated with sodium and calcium. The RVI and SV are fundamentally determined by the average thickness of smectite particles in the sol that swell osmotically after Na-saturation and form larger packets after Ca-saturation. Among the three smectites, the smectite taken from the argillized layer where no slip surface developed showed the lowest degree of osmotic swelling and packet formation. This smectite was found to be composed of montmorillonite and beidellite-nontronite in a roughly equal amount, whereas the smectites from the slip surfaces were mostly of montmorillonite-type. The residual strengths of the Kamenose soils are considerably varied at the effective normal stress below 100 kPa. This variation of the residual strengths was not well explained by the differences in the

Landslide stability analysis utilizing shear strength of slip surface soil: Asato and Tyunjun landslides, Okinawa, Japan.

In the stability analysis of Asato and Tyunjun landslides, the average shear strength acting along the slip surface has been calculated utilizing results of laboratory shear tests of the slip surface soils. For the Asato landslide, which is a large-movement along the whole slip surface, it is considered that most of the slip surface zone has been lying at residual state and the remaining parts at fully softened state. Average shear strength parameter, (c′, φ′ ), acting along the slip surface has been determined as c′ = 0 kN/m andφ′ = 12.3°. Thus, the average shear strength was close to the residual strength, which is reflected in the well-defined slickenside on the slip surface. For the Tyunjun landslide, the slip surface consists of a fractured-mudstone zone in the toe part and slickenside in the upper/middle part. In the stability analysis, it is considered that in the upper/middle part of the slip surface residual strength has been mobilized, while in the toe part peak strength of the fractured-mudstone has been utilized. Thus, the calculated average cohesion for entire slip surface is greater than zero. INTRODUCTION Landslides have several contributory causes, and among them, nature of soil is important for a landslide and the shear strength of the soil at the slip surface is directly related to sliding. For effective control works for landslides, what is important in the safety evaluation of landslides is to understand shear strengths of the soil and rock along the slip surface and decide an appropriate average shear strength parameter acting along the slip surface (average cohesion c′, average angle of shearing resistance φ′ ). However, in stability analyses with the 1246 GeoFlorida 2010: Advances in Analysis, Modeling & Design (GSP 199)