The density and confining pressure of coarse-grained soils affect their mechanical properties. Dense soils tend to soften and expand under low pressure, but harden and shrink under high pressure. Higher density and pressure lead to higher shear strength. Initial void ratio influences deformation, with lower ratios resulting in less deformation. Density determines the initial elastic modulus, which affects shear strength. Volumetric strain initially shrinks and then expands during compression tests, with the extent determined by density and stress levels.