ABSTRACT
Mohr circles for three soil samples and the Mohr envelope are shown in Fig. 8.20. Though all the samples had the same initial conditions, the deviator stress increases with the increase in the all-round pressure (T3 as shown in the figure. This indicates that the strength of the soil increases with increasing values of (T3. The degree of saturation also increases with the increase in (T3. The Mohr envelope which is curved at lower values of (T3 becomes almost parallel to the (T-axis as full saturation is reached. Thus it is not strictly possible to quote single values for the parameters Cu and l/Ju for partially saturated clays, but over any range of normal pressure (Tn encountered in a practical example, the envelope can be approximated by a straight line and the approximate values of Cuand l/Ju can be used in the analysis.
Effective Stresses If the pore pressures are measured during the test, the effective circles can be plotted as shown in Fig. 8.21 and the parameters c' and l/J' obtained. The envelope to the Mohr circles, when plotted in terms of effective stresses, is linear.
