Examples of variation of resilient modulus and permanent deformations of subgrade soils with moisture content are presented in Figs. 10.15 and 10.16. Figure 10.15 presents results obtained on a clayey sand (14% fines, optimum moisture content
wOPM = 8%).
Figure 10.16 presents results obtained for a silt (85% fines, optimum moisture content wOPM = 14%). For the 2 soils, the resilient modulus (determined for two different levels of stress) decreases by a factor of 3-4 when the water content increases from wOPM — 2% to wOPM + 2% (typical in-situ moisture contents). For the same change, the permanent axial strains (determined after 200 000 load cycles with cyclic stresses p = 26 kPa and q = 80 kPa) increase considerably.
Brull (1983) performed triaxial tests on 2 different soils, a loam (from Sterrebeek in Belgium) and a slightly clayey sand (from Noucelles in Belgium). The tests were carried out for different dry volumetric masses, for suctions between 0 and 600 kPa, for different confining pressures (between 10 and 50 kPa) and for different deviatoric stress (between 5 and 25 kPa). The soil water characteristic curves (also known as retention curves) as a function of the volumetric mass of the samples are presented in Fig. 10.17.
The Resilient Modulus, Mr, of the different samples were determined from the triaxial tests. The influence of the volumetric mass and stresses have been analysed. For the tested materials, Brull attempted to establish a linear correlation between the Resilient Modulus, Mr, and the suction, s (Fig. 10.18).
a.
Cui (1993) tested a remoulded Jossigny silt in an unsaturated state and gave an evaluation of Resilient Modulus, Mr, and shear modulus, Gr, as a function of confining pressure and of suction level (Fig. 10.19).
