THE EFFECTS OF SLAKING ON THE ENGINEERING BEHAVIOR OF CLAY SHALES (CRITICAL STATE, FISSURES, STRENGTH, WEATHERING)

Numerous foundation and slope stability problems worldwide have been contributed to the presence of clay shale deposits. Present experimental and theoretical methods used in geotechnical engineering practice are inadequate for assessing the stability of clay shales. The major difficulties with clay shales are attributed to two properties: they are intermediate in behavior between rock and soil, and they tend to transgress from rock-like to soil-like materials within relatively short time-frames.; Evidence suggests that softening along fissures is important to the rapid loss of strength in clay shales. Yet, geotechnical literature is surprisingly devoid of studies concerning theoretical or experimental aspects of fissure deterioration in clay shales. Additionally, clay shales invariably exhibit a strong tendency to slake, or disperse, during rewetting, a property which certainly contributes to the softening of clay shales. However, few reported studies have investigated the slaking resistance of geological materials under conditions of confinement found in the field, while no reports were found which investigate the effects of slaking on strength or strain behavior.; The research presented in this dissertation provides initial theoretical and experimental assessments of the effects of fissure deterioration on the engineering behavior of clay shales. In particular, the drastic decreases in strength resulting from slaking are examained in detail.; The author introduces the possibility of incorporating the effects of slaking into the critical state soil mechanics model. The role of slaking is seen in this context as simply another path for altering the water content of the clay shale, while the strength envelope remains constant.; Laboratory experiments involving triaxial compression tests were performed on Pierre shale samples which had undergone various degrees of slaking under confinement of 10 psi. The results from these tests show very significant reductions in strength (up to 80%), resulting from a single slaking cycle. The shear strength data from both unaltered and softened samples were successfully normalized using critical state concepts, and displayed a well-defined two-segment failure envelope. This suggests that drastic lateral and temporal variations in the strength of clay shale deposits, which result from slaking, might be accounted for using the critical state approach.