Many geotechnical engineers who apply Coulomb's equation (1) in plastic limit calculatlons are not aware that Coulomb stated that newly disturbed soil has no cohesion, Values of cohesion c and friction <φ> used by geotechnical engineers for undisturbed soil or excavated and recompacted soil should reflect the contribution of Taylor's interlocking to peak strength. The lack of cohesion in excavated and re-compacted soil increases the importance of ductility in soil. Soil should not be compacted too much below critical state density. Over compaction to obtain higher stiffness and strength increases the risks associated with cracking and seepage.