Shear strengths of several clay shales are synthesized and compared. variability of stress-strain curves indicates the material variation and complex structure inside each sample. Information obtained from the variability of these stress-strain curves could be used to estimate the overall material variability and bulk strength for design and analysis. Case histories in clay shales are summarized, and corresponding causes of slides and failure modes are discussed. Problems associated with clay shales and factors controlling the behavior of shales are analyzed and revealed. Several factors have been found to control the stability of slopes in clay shales and overconsolidated stiff fissured clays. Presence of structural defects and weak layers could lead to initiation of slope instability. Due to the presence of weak layers and anisotropic behavior in the material, translational block slides are often seen in the slope failures.


Shale is the most commonly encountered material in civil construction works. There are several types of shales, classified depending on their material composition and nature of any cementation present. It is important to be able to distinguish different shales, because their properties and engineering behavior could be very different from each other.

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