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Mineralogical composition, measured with x-ray diffraction for soil specimens collected from more than 80 natural disaster areas, show smectite, kaolinite, mica, feldspar, and quartz as major constituent minerals. Based on the results of more than 35 mixtures of smectite, kaolinite, and quartz in different proportions, a new correlation method was proposed for estimation of the residual friction angle (ϕr′) with the proportion of the minerals. The mineralogical compositions of the natural samples were used to estimate the ϕr′ based on the proposed triangular model. The estimation method resulted in values as close as 90% to the measured ϕr′ , and as close as 80% to the case of 53 samples tested by other researchers. The paper incorporates the correlation of ϕr′ with the liquid limit, the plasticity index, the clay fraction, the specific surface area, and the proportion of smectite. Various ranges are proposed, according to the influence of the constituent clay minerals. In addition, the applicable range of the correlation methods in practice were also verified.
Tiwari et al. (Thu,) studied this question.