In analysis of the causes of the landslide that occurred at Kashio in Central Japan, the author has paid close attention to exchangeable ions contained in soil and the effect of groundwater on soil at the site. Chemical analysis shows that the soil forming the unstable slope is partly saturated with calcium ions in its natural state, and that the artificial soil which is derived by supplying with calcium ions to saturation exceeds the original one in shearing strength. The author has thus reached a conclusion that the stability of slope was upset through loss of calcium ions out of slope soil by seepage water.

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Basic idea and empirical ground for the standard criteria, now in use in Hokkaido, as to the depth of pavement structure including base and subbase of select materials are stated.Some troublesome phenomena, such as warping and cracking of pavement, and growth in residual subgrade of ice masses have been observed in frigid districts. Some detailed studies, based on the theory of heat conduction, of frost aspects of residual subgrade and resultant depth of frost penetration after replacement or cover with coarse grained select material are given.Conception for determining the proper depth of pavement structure or of select fill and a suggestion for making use of material of high moisture content as reducing agent for frost penetration are presented.

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The author carried out unconfined compression tests on undisturbed samples of landslide soils having slip surfaces.Test pieces were polished with steel-wool and cloth after tests, to observe their stratification.Soil layers having slip surfaces in situ were observed as layers with anisotropic black varves or with dominant boundary between clayey layer and other layers.Unconfined compression failure planes in each test piece had relations to locations of layers or boundaries.Shear stress on the first appearance of failure on the planes were smaller than that on other planes.

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The earthwork for railroad embankment had to be suspended when a serious shortage of fill material was suddenly apprehended. The completed section of embankment and the fill material that remained untouched at borrow pits were thoroughly investigated with a dynamic penetrometer and the conclusion has been reached that a lower soil conversion factor of the fill material than estimated for design purpose is largely responsible for the heavy shortage of the fill material.

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Index properties and shearing strength of soils and mudstone taken from several landslides of Tertiary fractured region were investigated. The results showed that the sliding soils, often referred to as "blue-black clays", have similar properties, and that the sliding diatomaceous earth has properties considerably different from the "blue-black clays". The bed rock of sliding areas, being mudstone in most cases, shows the phenomenon of slaking. The features of slip planes were found in some of the test pits burrowed in sliding areas.

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