Strength and Dilation Behaviour of a Reconstituted Sand-Shell Mixture

Abstract

Calcareous sand usually composed of particles of carbonite origin of relatively weak structure, high void ratio and low grain strength. These sands show different strength and dilation behaviour than quartzite sands due to the existence of calcareous material. Several locations on the Libyan coasts are containing calcareous sands or sands with considerable amount of calcareous material such as broken shells or shell fragments. The present study is concerning in investigating the effect of the amount and the size of the calcareous material on the shear strength behaviour of sand shell mixtures. Samples were obtained from a coastal site near the city of Benghazi. The sand shell mixtures were prepared at practically similar unit weight and at a dense state. Two series of tests were performed in direct shear box of 100x100 mm on reconstituted samples of dry sand, the first was mixed with proportions of 20,40 and 60 % of broken shells by weight of material, and the second was mixed with only 20% of shell sizes ranging from 0.85 mm to 4.75 mm. The results indicated generally increasing of the peak angle of shearing resistance (фp) and reduction of dilation response of sand with increasing the amount and size of shell material. Furthermore, larger compression with increasing content and size of shell material is also observed due to the crushing of shell material during shearing.