In-situ shear strength by centrifuge modelling

This thesis is an experimental study of shear strength in anisotropic clays by means of centrifuge model tests, cone penetration tests, and vane shear tests. To understand the variation of peak shear strength, void ratio, and overconsolidation ratio, a new centrifugal testing technique is designed to obtain constant overconsolidation ratio profiles with varying void ratios, called the "Descending Gravity Testing" (DGT). The parameters controlling the generation of peak shear strength are understood and quantified. As a result of this function, a new material and rate dependent surface, "Cinici surface", is found in the e-OCR-Su space. This surface is defined as a "Structural State Capacity Surface" since it relates the anisotropic structure to structure inherent capacity and properties. Cinici surface gives an explanation for the relationship between lateral earth pressure, internal friction angle and interlocking, whereas a new method is proposed for their quantification. A new function for the estimation of excess pore pressures generated by cone penetration is found. Combining this function and Cinici surface, a new model is proposed, called "CU model". CU model is a structure based model which provides reliable estimates of shear strength for in-situ saturated clays using the knowledge of void ratio and overconsolidation ratio. Also, using Cinici surface, it sheds light on the mechanism of interlocking and friction. And finally, by combining Su-e-OCR and uex-e-OCR relationships, it estimates the void ratio and OCR profiles of anisotropic clays from piezocone penetration test results. Moreover, obtained cone factors as a result of cone penetration and vane shear tests are presented, cone friction sleeve measurements are investigated, recommendations are given for improving testing techniques in the centrifuge, and possible future research topics are pointed out.