Taheri, A.Tatsuoka, F.2015-06-182015-06-182015Acta Geotechnica, 2015; 10(1):131-1551861-11251861-1133http://hdl.handle.net/2440/92360The effects of loading histories on small-strain and large-strain stiffness of a compacted cement-mixed well-graded gravelly soil were evaluated by consolidated drained triaxial compression (TC) tests. Various cyclic loading histories were applied during otherwise continuous monotonic loading at different confining pressures, r h s, and multiple-step loading with stepwise increase or decrease of r h . To evaluate small-strain stiffness, minute unload/reload cycles were applied during TC loading. The value of peak-to-peak secant modulus from a minute unload/reload cycle was defined as the equivalent Young’s modulus, E eq . The average of E eq values measured during continuous monotonic loading at low deviator stresses was rather close to the elastic modulus, E e . As the E e increased with an increase in the axial stress, the E eq value increased first and then decreased due to an increase in creep strains. The stress–strain behaviour after the start of a large-scale yielding and the peak shear strength is not noticeably affected by the previous cyclic loading with relatively large stress amplitude. However, the large-strain stiffness during reloading is significantly affected by the following factors controlled by pre-cyclic loading history; (a) strain hard- ening; (b) strain nonlinearity; (c) hysteresis effect; (d) vis- cous effect; and (e) damage to bonding by immediately preceding large unloading. The tangent stiffness, E tan ,ata given stress level during reloading becoming larger with an increase in the effects of factor (a) and smaller by the effects of factors (b), (c), (d) and (e). In addition, increase of r h has a negative effect on stiffness of primary loading curves and a positive effect on stiffness of reloading curves. The effect of loading history on the small-strain stiffness in terms of equivalent Young’s modulus, E eq , was found to be significant. This effect depends on various factors. Four factors—axial stress level, strain-hardening effect, creep effect by the viscous properties and damage due to a loading history—were identified to be responsible for equivalent Young’s modulus, E eq variations. Axial stress increase and strain-hardening effect both increase E eq , making E eq closer to the E e . However, creep strains by the viscous properties and damage due to a loading history both decrease E eq .en© Springer-Verlag Berlin Heidelberg 2014Cement-treated soil; large strain; loading history; small strain; stiffnessJournal article003002207110.1007/s11440-014-0339-70003482999000082-s2.0-84921880180171889Taheri, A. [0000-0003-4176-5379]