Small strain stiffness and non-linear stress-strain behaviour of cement-mixed gravelly soil

The stiffness at small strains and non-linear stress-strain relation of compacted cement-mixed well-graded gravelly soil as well as the ageing effects were evaluated by drained triaxial compression tests on compacted moist specimens cured for different periods at isotropic and different anisotropic stress states. In all the tests, the initial stress-strain relation at small strains less than about 0.001% was essentially elastic and the initial Young's modulus, E-0, was essentially the same as the E, value evaluated by applying unload/reload cycles under otherwise the same conditions. The E-eq values were rather independent of strain rate. The E-eq value from the first unload/reload cycle applied during otherwise continuous ML became noticeably lower than the elastic modulus evaluated at the same stress state, more as approaching the peak stress state. After a number of small unload/reload cycles and long sustained loading, the E-eq value became closer to the elastic modulus due to a decrease in the viscous effects. The ratio of E-0 to the compressive strength (qnm) was similar to that of concrete but noticeably larger than those of uncompacted cement-mixed soil, sedimentary softrock and unbound gravelly soil. Both E-0 and q(ma)x increased with time by ageing, while the E-0/q(max) ratio decreased with time. When ML was restarted at a constant strain rate after ageing with a shear stress, the tangent stiffness became very high for a large stress range with a substantial change in the non-linearity of stress-strain relation.