Comparison of Shear Strength of Cohesionless Soil in Direct Shear and Simple Shear Tests Under Repeated Loadings

Designing the stability of pavements or embankments is a challenging issue in the geotechnical engineering sector. Many studies have been carried out to investigate the shear strength of cohesionless soil under monotonic direct shear (DS) and simple shear (SS). However, few studies have evaluated the influence of repeated loadings on the strength of soil. The goal of this study is to evaluate the strength characteristics of glass bead samples using repeated loadings. The same procedures were applied for all samples in two tests. Samples were tested under drained strain-controlled mode for each normal stress (σn) of 50, 100, and 150 kPa under shearing rate of 0.1 mm/min. The experimental results show that the peak shear strength in DS gave generally higher than that in the SS. The shear stress ratios between two tests (τSS/τDS) ranged within 0.95 ± 0.10. The friction angles in DS were in a wide range of 26.1°–28.7°, while those obtained in SS were a narrow range of 26.6°–26.8°.