Geotechnical characterization of the calcareous sand in northern coast of Egypt

Abstract The surface layer of the northern coastal line in Egypt is mainly comprised of calcareous sand, resulting from erosion of limestone and calcarenite ridges. These calcareous sand formations, are considered problematic due to their possible crushability and high compressibility. Reconstituted calcareous sand is mixed with different ratios of broken shells to investigate the effect of particle crushability on the strength behavior. The strength and crushability are evaluated using laboratory direct shear, triaxial compression and one-dimensional consolidation. Crushability of medium to fine uniform calcareous sand is found to be insignificant. Reconstituted sand-shell samples that contain 30% or more by weight of broken shells have exhibited a reduction of about 20% in the peak angle of shearing resistance. Sand-shell mixtures, with broken shells content of 30% or more, show significantly higher compressibility and consequently lower soil modulus. Simplified equations are proposed to express the degradation of the constrained modulus due to crushability.