A Study of Snow Induced Landslide Behavior And Its Observation System

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Most of landslide disasters in the snowy regions are considered to be caused by deposited snow, and greentuff geological environment of composite clastic rocks and bentonic soft clays. However, detailed behavior of snow induced landslides, mechanical properties of clastic greentuff are unknown, and still remain to be studied to develop observation system of landslides especially in the snowy seasons.The main objective of our present research project for a period of two years from 1993 to 1994 is to study above mentioned points. The results obtained in the research project are summarized as follows.(1) According to the collected records on landslides, huge landslides tend to take place at the late spring because of melting snow and accompanying softened soils.(2) Soil sampling in the landslide areas in the heavy snowfall regions and laboratory tests of landslide soils were performed, and a constitutive equation for swelling behavior was found, and it was fit for swelling phenomena for all bentonic soils.(3) From testing results, many effective relationships among the mechanical properties of greentuff soils were obtained, for example, high relationship between residual shear strength and residual angle of internal friction, besides a special relationship between the shear strengths and normal stresses by water contents were found, i.e., Coulomb's law for failure mechanism was not fit for the samples whose water content higher than 35%.(4) To review the risk degrees of each potential landslides which were pointed out by local government in 1991, principal component analysis method was applied, and new potential landslide maps were thus made for Akita, Yamagata, and Miyagi ptrefectures.These are very useful to prevent and control landslide disasters.(5) Automatic observation system for snow weather situations was set up at the top of landslide area, and effective results were obtained to make clear the behavior of snow induced landslides.