The meaning and practical significance of the cohesion intercept in soil mechanics
Abdel-Ghaffar, Magdy Emadel-Din Mohamed
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https://hdl.handle.net/2142/23778
Description
Title
The meaning and practical significance of the cohesion intercept in soil mechanics
Author(s)
Abdel-Ghaffar, Magdy Emadel-Din Mohamed
Issue Date
1990
Doctoral Committee Chair(s)
Mesri, Gholamreza
Department of Study
Engineering, Civil
Discipline
Engineering, Civil
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
An extensive literature study has resulted in a data base on both the laboratory measured cohesion intercept, c$\sp\prime$, and field mobilized cohesion intercept, c$\sp\prime$(mob). The data base includes values of c$\sp\prime$ and c$\sp\prime$(mob) for over 300 natural deposits throughout the world. The soils which include soft clays to shales and residual soils, have a range of water content of 7-330%, liquid limit of 15-420%, plasticity index of 3-285%, liquidity index of $-$5.5 to 3.5, sensitivity up to 500, clay fraction of 2-93% and, activity of 0.1-9.6. The preconsolidation pressure ranges from a low of 44 kPa to a high of 14000 kPa. The values of c$\sp\prime$ have been correlated to both the stress history and plasticity index of the soil.
A new expression for the non-linear failure envelope in the overconsolidated stress range has been developed and the parameters included in it have been evaluated. The shear strength in the overconsolidated stress range is a function of the effective normal stress, preconsolidation pressure, friction angle of the material in its normally consolidated state and a constant 'm'. For the sensitive clays of Eastern Canada, m is a function of the effective stress level while for other clays, m is independent of effective stress level, however, it is a function of the plasticity index.
A new procedure for conducting the effective stress stability analysis has been put forward, whereas for the first time slides peak strength is used to locate the critical slip surface, however, mobilized strength between peak and residual is used to determine factor of safety.
Sixty seven case histories of drained and undrained failures of slopes and embankments have been analyzed. For the sensitive clays of Eastern Canada, an insitu mobilized shear strength envelope was obtained. For other clays, the ratio between the shear strength mobilized in the field and the laboratory measured peak shear strength was correlated to the plasticity index and consistency of the soil.
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