Determination of shear strength in unsaturated fine-grained soils

Unsaturated soil is used for soils where the voids are not completely filled with water. Experimenting for unsaturated soils takes a long time and geotechnical problems for these soils are more difficult to solve. In this study, the unsaturated mechanical behavior of the soils of the Adapazarı formation was investigated. Samples with four different contents were used in the study. First of all, soil classes were determined by determining the physical properties of the samples. The conventional triaxial cell shear test device was modified and made suitable for the unsaturated test method. Consolidated-Drained (CD) triaxial cell shear test method was preferred in order to examine the mechanical behavior. In all triaxial cell shearing experiments, samples were shearing in multistages in order to obtain more data from a small number of samples. In the study, suction measurements were performed using filter paper and pressure plate methods and soil-water characteristic curves (SWCC) were created. Matric suction values, which are the parameters used in the triaxial cell shear test, were determined from the drawn SWC curves. Consolidated-Drained triaxial cell shear tests were carried out for 1 series (4 samples) of saturated soils and 5 series (20 samples) for unsaturated soils. For the unsaturated soil results, the plot of the failure envelopes of the N-1, N-2 and N-3 samples was obtained linear with the increase of capillary suction value. The failure envelope of the N-4 sample, on the other hand, does not continue linearly after the air entry value obtained as a result of the SWC curve and is drawn non-linearly. It was concluded that the b angle obtained from the samples increased with the increase in the amount of sand in the sample. With the results obtained from all experimental studies with Method 1 and Method 2, the slip surfaces of the samples were drawn in 3D and the failure envelopes were also obtained from these 3D surfaces. As a result of the experimental studies carried out with both method 1 and method 2, the smallest cohesion value was obtained from sample N-1. The highest cohesion value was obtained from sample N-4.