TENSILE-STRENGTH OF DRY, REMOLDED SOILS AS AFFECTED BY PROPERTIES OF THE CLAY FRACTION

Changes in tensile strength with clay type, clay particle size, and am ounts of spontaneously and mechanically dispersible clays were assesse d for dry, remoulded samples of eight Australian Vertisols and Alfisol s varying in clay mineralogy. The effects of different clay content an d particle size on tensile strength were also measured. The average pa rticle sizes of whole clay, and of spontaneously and mechanically disp ersible clays were also determined. Tensile strength of soils was infl uenced by the type and amount of clay present, clay particle size, and amount of dispersible clay. Soil strength increased with increasing c lay content. When the clay content increased beyond 20%, there was a d ramatic increase in soil strength indicating the possible role of part icle arrangement. Correlations between different clay types, clay part icle sizes, cation exchange capacity and tensile strength clearly illu strated that the sensitivity of tensile strength to these factors was greatest in soils dominated by smectite, followed by illitic and then kaolinitic soils. Tensile strength of soils was positively and signifi cantly correlated with both spontaneously and mechanically dispersible clays, A significant negative correlation was obtained between clay p article size and tensile strength for illitic soils, whereas the same linear relationship was not significant for smectitic soils. However, a significant negative exponential regression was obtained between the cube of clay particle size and tensile strength when the results of a ll soil samples were pooled together. Transmission electron micrograph s (TEM) showed a wider clay particle size distribution in smectites th an in illites, Soils with the highest amounts of fine clay and the wid est clay particle size distribution had higher tensile strengths. The size of spontaneously dispersed clay particles was smaller than that o f mechanically dispersed clay. No difference in clay particle size was found between spontaneously and mechanically dispersible clays from m ixtures of a fine clay with a basic sand and silt matrix, Regression, collinearity diagnostics and principal component analyses were used to analyse the data. A high correlation was found between the cation exc hange capacity (CEC) of clays and soil strength. The principal compone nt analysis indicated that spontaneously dispersible clay, percentage of randomly interstratified minerals (RIM) and CEC were important fact ors in predicting the strength of remoulded soils.