Strength and consistency of artificial clay — carbonate mixtures: Simulation of natural sediments

Abstract

Marl, a common rock within carbonate sequences in Israel, occurs as an intimate mixture of varying proportions of clay and carbonate. The diagenetic process involved in the formation of the rock is controlled by the physical and chemical properties of the material as it progresses from sedimentation through diagenesis to lithification. To provide a better understanding of the formation of these rocks, natural sediments were simulated in the laboratory. This was done by mixing varying proportions of Upper Cretaceous smectites (bentonite and montmorillonite clay) and Jurassic kaolinite from Makhtesh Ramon with Eocene chalk from the northern Negev. The strength and consistency of these mixtures was then determined. The relationship of Plasticity Index to Liquid Limit, with a correlation coefficient of 0.945–0.982, shows that the bentonite mixtures are of medium to high compressibility in comparison to the kaolinite mixtures, which have a low plasticity. The montmorillonite mixtures have a medium plasticity. Free swell of the bentonite and montmorillonite mixtures is in general twice that of the kaolinite mixtures and decreases in all cases as the carbonate content increases. The effective range in friction angle, under drained conditions similar to those occurring in the natural environment, and saturation of up to 80%, is generally consistent with increasing carbonate, being only slightly higher in the montmorillonite mixtures. Cohesion is higher in the bentonite mixtures. Marls containing bentonite or montmorillonite undergo relatively higher volume changes than kaolinite muds. They also deform plastically, being more sensitive to changes in natural water content. Generally, kaolinite muds are more stable and less deformed during lithification.