The behaviour of granular embankments with and without fabric inclusions

Triaxial stress-strain and volume change curves for the twoinitial porosities considered are shown in Figs. 1.2 and 1.3.Several tests were also carried out at other different values ofinitial porosity and the variation of friction angle ~ withinitial porosity could be established by plotting a regression linethrough the experimental points as shown in Fig. 1.4. The highscatter in the points is attributed to the fact that ~ is dependenton the confining pressure 03.The Mohr envelopes for almost all soils are curved to someextent, and the wider the range of pressures involved, the greaterthe curvature (Wong and Duncan, 1974). In order to determinethe relationship between ~ and 03 for Leighton Buzzard sand thefollowing procedure was applied.The value of ~ was determined from each triaxial test,assuming the envelope for that circle to pass through the originof stress. It was usually found that the values of ~ decreased inproportion with the logarithm of the confining pressure as suggestedby Wong and Duncan (1974), and expressed by the following equation°3- 6.~ loglO (-)Pao = 0o-1.1In this equation ~o is the value of ~ for 03 equal to theatmospheric pressure p and 6.~ is the reduction in ~ for a lO-foldaincrease in °3• Figures 1. 5 and 1. 6 show the variation of thefriction angle ~ with 03 for medium dense sand no = 39.2% and densen = 34% respectively. The constant ~ and 6.~ in equation 1.1o 0were determined from the triaxial test results (Fig. 1.5 and 106).The average value of 03 which is expected in the modelembankment was estimated. This value was substituted in equation1.1 in order to determine a relevant single value of ~ to be usedin the theoretical analysis. The resulting value of ~ is givenin table 1.1 for both dense and loose cases 0The triaxial stress-strain and volume change curves for the twodensities considered (Fig. 1.2 and 1.3) were used to determine thehyperbolic parameters required for the nonlinear stress-dependentrepresentation of the soil behaviour according to the procedure andrelationships explained in Chapter 3. These relationships are shown