AbstractThe effect of overconsolidation on the monotonic shearing resistance of three nonplastic soils (a clean sand, a clean sand and fine tailings mixture, and a fine tailings) was examined using laboratory Ko-consolidated constant volume direct simple shear (DSS) tests performed on contractive specimens. Two different overconsolidation methods were used. Isotopically consolidated undrained triaxial compression (CIU-TC) tests from the literature also are presented. The stress history and normalized soil engineering properties (SHANSEP) equation was used to interpret the relationship between strength ratios and overconsolidation ratio (OCR). The SHANSEP equation appears to capture the increases in strength ratios, at both the peak and the critical states, with OCR. However, only the increase in undrained critical state shear strength ratio, su(critical)/σvo′, with OCR can be derived based on critical state soil mechanics concepts using the swelling index, Cs, compression index, Cc, and slope of the critical state line, λ10. In addition, theoretical derivation showed that the strength ratio increase can be affected by the method of overconsolidation, especially when Cc/λ10 is small. Overall, the SHANSEP equation parameter m obtained from the constant volume DSS and CIU-TC tests was in good agreement with theoretical values.