Identification of the microfabric of kaolin clay and its impact on the shear strength behavior

A new method for identifying the microfabric (geometric arrangement of platelets) of cohesive soil using X-ray diffraction technique without the need for a pole figure device has been developed in this study. This method is based on identifying the occurrence of basal and prism peaks in a given X-ray diffraction pattern and their relative intensities observed in the pattern. Five different specimen preparation techniques are used to prepare the Kaolin clay specimens with different particle orientations to identify their microfabrics using X-ray diffraction analysis, and the results are assessed in conjunction with high magnification SEM (Scanning Electron Microscope) images. The proposed method does not require impregnation of clay with alternate pore fluids/epoxy, and is able to identify the undisturbed microfabric of clay sample at its natural water content. This method is further used for evaluating the variation in microfabric of slurry consolidated specimens of Kaolin clay due to triaxial shearing under compression and extension loading conditions.; The impact of microfabric on shear strength behavior of Kaolin clay is studied for the variation of confining pressure, stress history, and loading/boundary conditions by performing a series of triaxial experiments using lubricated ends. The importance of using appropriate drainage conditions for the lubricated ends in triaxial device is discussed based on the experimental observations during drained and undrained triaxial tests performed at three different drainage conditions. Using improved drainage conditions, a series of triaxial compression and extension tests are performed on normally consolidated and heavily overconsolidated specimens of Kaolin clay with two extreme microfabrics (dispersed and flocculated) under drained and undrained conditions. Three different values of confining pressure are used to evaluate the effect of confining pressure on shear behavior of dispersed and flocculated specimens of Kaolin clay. A comparison between the drained and undrained shear response is presented for the variation in the loading conditions and the stress history of soil. This study also includes a discussion on the occurrence of strain localization within the clay specimens and the impact of microfabric, confining pressure, loading conditions, stress history, and drainage conditions on the pattern of strain localization using digital image analysis (DIA).