The 'angle of internal friction' (φ) of a dense sand is typically:

Dense sand: φ = 35°–45° (dilatant on shearing). Loose sand: φ = 28°–32°. Clay: φ = 0° for undrained (saturated), 10°–20° for drained. φ increases with: angularity, uniformity, relative density. Dense sand dilates on shear → requires more energy → higher φ. The peak φ reduces to critical state φ at large strains.

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