抄録
Soil samples collected from a few landslides, debris flow, slope failure and volcanic areas in Japan have shown smectite, kaolinite, halloysite, feldspar and quartz as main dominating minerals. Commercial bentonite having quartz, crystballite and smectite and commercial kaolin, consisting of kaolinite, halloysite, feldspar and quartz has been mixed up with Toyoura sand to make the samples of various proportions of smectite, feldspar, halloysite and kaolinite in quartz. Residual internal friction angle (φr) of the bentonite-sand mixture was not varied considerably for the bentonite proportion upto 15%. Likewise, φr was more or less constant with the minimum value i.e. 3.7° for more than 50% bentonite. Value of φr was gradually decreased for the mixture from 15% to 50% bentonite. Value of φr for kaolin-sand mixture had decreased continuously from 15% to 100% kaolin proportion. In case of kaolin-bentonite mixture, the minimum φr was obtained for more than 30% bentonite. The shear strength of the mixture was controlled mainly by bentonite proportion. The effect of kaolin was high for the proportion of kaolin less than 10%. For proportion of kaolin more than 20%, sand less than 50% and bentonite more than 30%, the φr was close to minimum. Strong relationship was obtained with liquid limit, plasticity index and weighted smectite proportion. Value of φr for actual disaster area samples were fitted well inside the envelope for kaolin and bentonite in the φr-liquid limit and φr-plasticity index charts. The research showed that the residual shear strength could be estimated roughly with the proportion of clay, liquid limit and plasticity index, for certain clay mineralogy.
