Mineralogical and geochemical studies carried out on intrafault materials collected at two outcrops of the Atotsugawa fault of Central Japan, which had been described in detail in the previous paper. A sample of the intrafault materials was divided into four fractions of 2μ>, 2-74μ 74-250μ and 250μ< by their grain size. Mineralogy and geochemical compositions were examined in each fraction of the sample. The three fractions of 2μ< have almost similar mineralogy and geochemical compositions. Mineralogically, the 2μ>fraction is including more amount of montmorillonite, illite and chlorite and on the contrary less amount of quartz, feldspar and calcite than the other three fractions. The geochemical compositions of the 2μ< fraction is rich in Al2O3, MgO, K2O and total H2O and poor in SiO2, CaO, Na2O and CO2, comparing with those of the other three fractions. It is disclosed that the mineralogy, geochemical compositions and grain size of the intrafault materials have close relationship one another and should be related to the formation process of the materials and the degree of their weathering or alteration.
In recent years, a large-scale cut-off wall has been constructed to cut the seepage flow of aquifers in those cases as the excavation works, the underground works and the underground dam in order to store the water resources in this country. It is very important to know several hydraulic effects of cut-off wall, such as the relation between the flow rate and penetration depth of wall, and the groundwater behavior resulting from the penetrated wall. This paper presents theoretically how to find the change of seepage flow rate and groundwater head by the partially penetrated cut-off wall on the basis of Aravin & Numerov theory. For the sake of practical use, the computation technique of hydraulic quantities under required conditions was proposed by the graph utilization method. The validity of method and theory was confirmed by some experiments of Hele-Shaw model.
In August, 1980, a great number of slope-failure occurred at Tomiura area, Noboribetsu City. In this area, late Pleistocene pyroclastic deposits of Kuttara Volcano are widely developed. Results obtained from this study are as follows: 1. The slope-failure is caused by heavy rains with maximum intensity reaching 40-60 mm/hour. 2. The original slope-failure is produced by the abundance of water absorbed by the piping system of the slope, is occurred at the cutting slope of the City Road and Route 36. 3. At the top of the natural slope, hollowed area, secondary collapse and gully erosion occurred, producing the debris flow. This debris flow ran down the valley wall taking off the surface soils and made the gullies.