Strength and Stiffness Characteristics of Unsaturated Hydrophobic Granular Media

Abstract

The nonwetting nature of hydrophobic soils, which results from wildfires or organic substances, may influence the shear strength and stiffness of granular soils. Since surficial soils are often unsaturated, their shear strength and stiffness are also affected by the magnitude of negative pore-water pressure. The goal of this study is to investigate the dominant factors affecting the strength and stiffness of hydrophilic and hydrophobic soils. Hydrophobic granular media were synthesized by a silanization technique with glass beads (D-50 = 0.25 mm) to a degree of saturation of S = 0, 5, and 10%. The prepared specimens were sheared using a direct shear device at various normal stresses. The shear waves were continuously monitored by bender elements. The experimental results showed that hydrophobic specimens had a lower shear strength than hydrophilic specimens due to lower friction, even though the hydrophobic specimen was under a denser packing condition. The shear stiffness was constant at small strains in the specimen composed of hydrophobic particles. However, as a result of the higher friction, the stiffness at small strains in the specimen composed of hydrophilic particles increased as the horizontal displacement increased. The results demonstrate that capillary force, interparticle friction, and packing density are important contributing factors to the shear strength and stiffness in hydrophobic soils.