Variation of Secant Young's Modulus in an Unsaturated Gap-Graded Granular Fill

It is of great significance to understand the variation of stiffness in unsaturated granular materials for predicting performance of earth structures. Variation of secant Young's modulus in an unsaturated gap-graded granular fill was investigated using unsaturated triaxial tests with local strain measurements in this work. Unlike the insignificant suction impact on shear strength in coarse-grained granular material, it seems that suction has greater effect on stiffness of the tested soil at small strain. Young's modulus enhances as suction and net confining pressure rise since average skeleton stress increases and soil skeleton gets more stable by meniscus water. In addition, specimen at larger suction possesses greater degradation speed than that at lower ones. One equation was adopted to estimate Young's modulus of soil. It shows that this equation may capture the variations of secant Young's modulus of soil under different suctions and net confining pressures.