Studying the effect of inherent anisotropy on undrained behavior of sand-silt mixtures

In some situations, dams need to be built on non-rock alluvial grounds such as sand and sand-silt deposits. Therefore, undrained behavior and strength of silty sands are of great importance. One of the critical factors in studying the behavior of sand-silt mixtures is inherent anisotropy, a natural soil characteristic that depends on its texture and is independent of the soil's initial stress state. This type of anisotropy causes the soil behaves differently under the rotation of the principal stress angle concerning the vertical direction. In this study, the effect of inherent anisotropy is studied in sand-silt mixtures using triaxial compression and extension tests. The results show that adding 30 percent of silt to the sand significantly reduces the effect of inherent anisotropy. However, adding more silt increases the inherent anisotropy effect again. Furthermore, the dilative and contractive specimen behaviors at different silt contents and their peak strength values differ in compression and extension tests. The peak strength in pure silt is larger than in specimens containing 50 and 70 percent of silt.