Nature of Soils, Plasticity and Compaction

This chapter encompasses the three major topics in relation to the basic characteristics of soil, and its physical properties. These topics are associated with the mass-volume relationships (Problems 1.1 to 1.5), index properties (Problems 1.7 to 1.9) including particle size distribution (Problems 1.6, 1.11 and 1.12) and compaction (Problem 1.10). The mass-volume relationships describe parameters, which control the engineering behaviour of the soil. These parameters are void ratio e , porosity n , degree of saturation Sr , air content Av , moisture content m or w , density of soil ρ (dry, saturated and natural), and density of solids ρ s or specific gravity of solids Gs . The particle (grain) size analysis, and plasticity indices are needed for soil classification. Problems 1.11 and 1.12 show the engineering application of the particle size analysis where the particle size distribution of a mixture is obtained by knowing the particle size distributions of the individual materials within the mixture. Soil compaction is necessary to improve its strength and bearing capacity. In a laboratory technique explained in Problem 1.10 the relationship between moisture content and density is demonstrated to yield the optimum moisture content corresponding to the maximum dry density.