Study on the mechanism and prediction of debris slides

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The result of research consists of the following four parts. The characteristics of debris slides: Debris slides occur in O order basins on slopes where mountain reliefs are small and bed rocks are subject to weathering or lowly consolidated. The characteristic of slope profiles vulnerable to debris slides is clarified by using the vertical variation of hydraulic conductivity, shear strength, N values and hardness of soil and reinforcement of soil by roots. Soil lapths and saturated alteral flow: Surface soil depths as a potential soil layer of debris slides were measured on three slopes, paleozoic, granite and tertiary. The results are expressed in terms of slope gradients. The process of topographical development of a O order basin is investigated with the change of curvetures of contour lines. The infiltrating process of storm water was measured on a slope with tensiometers and piezometers. Analysis was conducted with hydraulic headmaps, reconstructing subsurface flow patterns on a typical Pliocene zero order basin. Pipes in soil are classified into two catgories: visible and invisible. In addition, the role of pipes for stormflow in soil is discussed. The variation of saturated hydraulic conductivity of surface soil becomes smaller as the size of a sammpling cylinder become larger. The best size for practical use is 15-20 cm in diameter.Analysis of factors affecting landslide occurrence: Fifty seven results of multivariation analysis of landslides in a heavy storm in various regions were collected and analysed. The analysis showed the importance of altitude which is closely related to various other factors. A dividing line is set at 900 m, above which altitude is most important and below which vegetation become most important. Effect of tree roots on slope stability: An infinite slope model andan upper bound model were applied to estimate the reinforcement of soil strength by tree roots. The result is discussed from various viewpoints.