Effects of Drying–Wetting Cycle and Fines Content on Hysteresis and Dynamic Properties of Granite Residual Soil under Cyclic Loading

In southern China, granite residual soil (GRS) is widely used as road base material. Thus, it is important to study the effects of hot and rainy climates and cyclic loads generated by trains on the dynamic properties of GRS. In this work, by means of dynamic triaxial tests, the effects of the number of drying and wetting (D–W) cycles, fines content and number of load cycles on the hysteresis curve, dynamic shear modulus Gd and damping ratio λ of GRS are systematically investigated. The experimental results illustrate the changes in the morphology of the hysteresis curve and dynamic parameters with the numbers of load and D–W cycles, as well as the fines content. Namely, the area S, center offset d, and residual strain εsp of the hysteresis curve decrease with the increase of load cycle number, increase with the growth of fines content, and first decrease with the increase of D–W cycle number, then slowly increase to stabilized values. However, the major axis gradient k exhibits exactly the opposite relationships. Meanwhile, the dynamic shear modulus Gd increases with the growing load cycles and decreases with the addition of fines content, and the damping ratio λ shows the opposite behavior. It is also shown that Gd and λ vary linearly with respect to logN, where N is the number of D–W cycles. The dynamic properties of GRS are mostly affected by the number of load cycles, which is followed by the fines content and then the number of D–W cycles. The influence of the latter two factors on the dynamic properties of GRS may be primarily due to contact form changes between soil particles.