Relationship Between Clay Mineralogy and Residual Shear Strength Through the Model Based on Shearing Mechanism of Soil

摘要

Soil samples collected from 35 different natural disaster areas had shown the domination of quartz, feldspar, smectite and kaolinite. Mixtures of commercial bentonite, kaolin and sand for 34 different combinations, prepared in the laboratory to resemble the mineralogy of those natural samples, had shown very good relationship of residual φ with liquid limit and plasticity index, showing separate boundaries for kaolin and bentonite dominated soils. Plotting of triangular relationships for smectite, kaolinite and other minerals with 3D arcGIS software was done to make iso- friction lines. There were 7 zones in the relationship diagram, namely, zone A, where both the proportions of smectite and kaolinite were equally dominant for residual φ values; zone B, where both smectite and kaolinite were dominant, but the influence of the former was higher; zone C, where effect of kaolinite was negligible and value of residual φ was influenced by the proportion of smectite only; zone D and E, similar to zone C but with a larger effect of smectite; zone F and G, where residual φ were close to that of pure smectite and quartz respectively. Estimated residual φ with the proposed triangular plotting estimation model based on the mineralogical composition had shown less than 7% variation with the tested residual φ of the same samples. Particle crushing and breakage of cementation bond between the finer and the coarser particles made l-2mm thick shear zone after a cycle of multi stage ring shear testing. Mineralogical compositions of the shearing zone samples before and after the ring shear tests were similar. In contrary, proportions of fines after ring shear test was very high compared to the initial proportions.