The effect of soil type on dry unit volume weight internal friction angle

Soils can be found not only in saturated form but also partially saturated or dry in nature. The basic engineering property of the soil that controls the stability of the soil mass under structural loads is defined as shear strength. The internal friction angle and cohesion of the soil can be determined by both laboratory and field tests. One of the most common tests to determine internal friction angle and cohesion values in the laboratory is direct shear tests. In the experimental study, the change of strength parameters of completely dry soils were investigated for different relative densities and normal stresses. Direct shear test, which is one of the most used in the literature, was used. For this study, the changes of strength parameters of completely dry soils for different relative densities and normal stresses were investigated. The comparison with the assumption that the cohesion of the sand is zero was made only based on the internal friction angle. The obtained internal friction angle, the relative density and normal stress relationship were examined by considering the grain size distribution of soils. Four different type of sands were used in this study. The essential properties of the sands, such as the median particle diameter (D50), coefficient of uniformity (Cu), and coefficient of curvature (Cc), were used to analyze the effects. Conclusions from the direct shear tests represent that the extent of the angle of shearing resistance of the well graded sand is higher than the poor graded sand. The internal friction angle is usually increasing with increasing the median particle diameter (D50) and the relative density (Dr). It was achieved that the friction angle varies depending on the grain size, type of sand, relative density and five normal stress applied. It was obtained that maximum and ultimate shear stress increases with increasing internal friction angle for the same relative density.