Effect of Fine Content on Soil Water Retention Curve (SWRC) of Sand-Silt Mixtures

This study investigates the effect of fine content (FC) on the water retention behavior of sand-silt mixtures. A series of laboratory tests were conducted to obtain the soil water retention curves (SWRCs) for clean sand and mixtures containing ۱۵%, ۳۰%, ۶۰%, and ۱۰۰% silt by weight, using two suction-controlled triaxial apparatuses. Matric suction was applied and regulated through the axis translation technique and the hanging water column (HWC) method. The tested materials included Firuzkooh ۱۶۱ silica sand and its homogeneous silt. All specimens were prepared with an initial void ratio of ۰.۷ and subjected to drying and wetting paths under a mean net stress of ۵۰ kPa. The results revealed that increasing FC substantially altered the soil structure and water retention behavior, particularly by affecting the air entry (AE) suction value and the pore size distribution. The findings emphasize the fundamental role of fines in controlling the water retention characteristics of sand-silt mixtures, offering practical insights for applications in geotechnical and environmental engineering. Additionally, the performance of two widely used SWRC models; the van Genuchten, and Fredlund-Xing; was evaluated. The results indicated that both models efficiently capture the water retention behavior of sand-silt mixtures with satisfactory accuracy.

Keywords:

Soil water retention curve (SWRC) , Fine content (FC) , Sand-silt mixtures , Unsaturated triaxial test , SWRC models