Role of the texture of fibrous clay minerals in the plasticity behavior of host materials (Plateau du Kik, Western High Atlas, Morocco)

• Fibrous clay rich soils are characterized by very high plasticity index.
• We highlight a new field of palygorskite in the Holtz and Kovacs diagram.
• Texture of fibrous clays controls the plasticity behavior of host materials.

Seven samples (MB2 to MB8) collected from the clays and silty clays formations belonging to the Paleogene sedimentary series of the Plateau du Kik (Western High Atlas, Morocco) were characterized for granulometric analysis, mineral composition, clay composition and textures and for Atterberg limits. All the studied samples are classified as MH–OH type soils according to the ASTM international standard. Palygorskite usually constitutes the more abundant mineral phase in all the samples (35 to 64). The liquid limit for the most samples is well above 50 indicating the highly plastic nature of the studied sediment. This work clearly evidences that fibrous clay rich clayey materials having similar grain distribution and identical mineral composition and contents can have very different plasticity behaviors. This suggests that the fibrous clay textures play a role of prime importance in the plasticity behavior of the studied materials.