The effect of over-consolidation ratio on undrained shear strength of Adapazari silt

Foundations are structural elements that transfer stresses from buildings to the soil layers. They are designed to operate without loss of load-bearing capacity and without exceeding settlement limits. Therefore, it is necessary to calculate the bearing capacity of a foundation during the design phase by considering the soil's shear resistance parameters. The shear strength of a soil is the maximum shear stress value that can be transferred to the soil. In summary, the shear strength of a soil corresponds to the value that represents its plastic equilibrium state. Since exceeding shear resistance can lead to failure, the shear resistance parameters are essential in Geotechnical Engineering. In saturated fine-grained soils under foundations that will be subjected to sudden loading, the undrained shear strength typically becomes effective. Silty soils, which are fine-grained, are formed by the fragmentation of quartz crystals. They exhibit low plasticity or are non-plastic, showing diverse behaviors under different conditions due to their expansion and contraction characteristics. The silts of Adapazarı are soils formed by the sedimentation of fine-grained fluvial material transported by the Sakarya River to the Adapazarı Plain as a result of the slowing down of water flow. In this study, an artificial silty soil was created by mixing bentonite clay with the artificial silty soil obtained from Adapazarı silt, which had been purified of clay under laboratory conditions, in varying ratios from 0% to 40% by weight. This thesis encompasses an experimental study aimed at determining the effects of different over-consolidation ratio values on the undrained shear strength of soils with varying clay contents. Accordingly, the reconstituted samples with different clay contents were first subjected to a state of over-consolidation and then tested in undrained (UU) triaxial tests. Sibling samples prepared using the slurry method to ensure saturation were individually consolidated under pressures of 200, 300, and 400 kPa and tested using triaxial cell shear tests. The test results indicated that as the over-consolidation ratio increases in soils with the same clay content, the shear strength also increases. Additionally, in silty samples, an increase in the clay content resulted in a decrease in strength.