Fabric changes along shear planes at the result of triaxial test in clayey soils

Most soils and rocks, when deformed in shear, develop shear planes across which relative displacement of fundamental particles take place. In the field, shear planes can be encountered as fault and landslide failure planes as well as failure planes in foundation soils failed as a result of excessive loading due to an engineering structure. The main purpose of this PhD study is to investigate fabric changes along shear planes in triaxial testing under principal stresses. In the study, the relationship between fabric changes and principal stresses along shear planes in CU and CD triaxial compression tests with different shear rates and unit deformations under 20 kPa confining or cell pressure was investigated.An artifical clay soil was prepared by mixing 33,33% muscovite mica sand and 66,67% clay. The soil mixture was put in a metal box and kept saturated for about one year under a pressure of about 0,028 kg/cm2 (2,78 kPa) in order to produce an artificial soil sample with an initial soil structure. First, cylindrical samples were taken from this artifically prepared soil and then one sample was used for consolidation and saturation while 9 was used for consolidated-undrained (CU) and 10 for consolidated-drained (CD), totaling 20 tests. 21 thin sections were prepared across the failure planes (actual ve theoretical) and studied using a microscope and appropriate computer programs. Rose diagrams of orientations of particles, voids and other constituents were prepared and evaluated. The results show that there is a relationship between soil fabric changes and maximum principal stress. Orientaion increases as pore pressure increases or vice versa. Also, orientation decreases away from the failure planes.