Well-graded dense saturated sands have high shear strength because:
A. Such sands have a better grade (superior type) of sand grains resulting in higher strength
B. Such sands have lower water content, which increases shear strength
C. Such sands have better interlocking of grains, higher inter-particle contacts and higher inter-particle frictional resistance resulting in higher strength.
D. Presence of water in such sands induces capillary pressure generating higher inter-granular stresses, which generate apparent cohesion and hence higher shear strength.