Effects of fine matters on strength and stiffness

Deposits of fine matters (silt and diatom microfossils) are a common feature in many sites around the world (including Ulleung Basin, Korea, Osaka Bay, Japan, and Mexico City, Mexico), and the existence of such deposits affects soil strength. The objective of this study is to investigate the effects of fine organic matters on the strengths and stiffnesses of soils using a triaxial apparatus incorporated with bender elements. The specimens used are artificial mixtures of sand and organic matters with different fine fraction in weight. Note that in terms of weight, the fines consist of 30% diatom and 70% silt. In addition, the shear waves were measured during shearing. The experiment results illustrated that the shear strengths of soil mixtures increased with increasing fines up to 20%, then decreased with increasing fines thereafter 20%. The elastic wave result shows that shear wave velocity decreases due to changes in the fabrics of soils caused by the increase of fines. The results of this study established a huge impact of fine particles on the strengths and stiffnesses of soils.