الفهرس 
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Abstract
An investigation has been conducted with the objectives of gaining a better understanding of the drained residual and fully softened shear strenths of cohesive soils, the shear strength mobilized in overconsolidated clay field case histories, and developing empirical relationships that describe the stress-dependent nature of the residual and fully softened shear strengths in terms of soil index properties. TO INVESTIGATE THE DRAINED RESIDUAL STRENGTH, A Bromhead ring shear apparatus was mdified to allow testing of overconsolidated, presheared, remolded soil specimens of different plasticity and clay-size fraction. Residual shear strengths measured using the modified ring shear apparetus were compared to shear strengths measured in conventional reversal direct shear tests on prect specimens and shear strength values back-calculated from well documented field case histories of slopes that had undergone previous sliding. The natural soils used in the residual and fully softened research have a range of liquid limit of 24 to 286%,plasticity index of 8 to 244%, and clay-size fraction of 10 to 88%.
New relationships describing the resdual and fully softened friction angles developed from the extensive ring shear testing were presented in terms of the liquid limit, clay-size fraction, and effective normal stress. Most of the existing resdual and fully softened strengths relationships are based on only one soil index property and provided a friction angle that is indepenent of effective normal stress. The importance of including the liquid limit, clay-size fraction, and effective normal stress in estimating the resdual and fully softened friction angles is illustrated using field case histories.
Several first-time slides through stiff flssured clay were also analzed to estimate the shear strength mobilized during failure. Based on these analysis and laboratory test results, design recommendations for the shear strength of stiff fissured clay involved in first-time slides were provided.
A reanalysis of the 1981 uostream slide in San Luis Dam was conducted to evaluate the shear strength redction caused by the dispacement included by drained repeated loading. The effect of plasticity and degree of overconsolidation on this shear strength reduction was also investigated.