Chang presents data from a variety of different in situ tests conducted in the soft marine clays of Singapore and Malaysia. Since current procedures for profiling the stress history of clay deposits via in situ testing rely primarily on empirical correlations, it is commendable that Chang uses several independent methods (oedometer, field vane, piezocone, and (or) dilatometer) to assess the in situ overconsolidation ratio (OCR) at each of the six sites. I have also been actively engaged in research in this area and would like to offer an approximate theoretical approach to the problem, specifically using the piezocone for profiling the in situ OCR. The results have been approximately calibrated against data from 83 different clay sites tested by piezocones (Mayne et al. 1990). The piezocone approach used by Chang for profiling OCR (eq. [ l l ] of the paper under discussion) requires an estimate of both the effective stress friction angle (4' ) and rigidity index (I, = G/su) of the soil. While the former parameter may be determined directly from laboratory triaxial tests, the proper determination of I, corresponding to the relevant strain level is less straightforward. Using spherical cavity expansion and modified Cam Clay concepts, the excess pore-water pressures measured behind the cone tip during penetration are caused by a combination of octahedral and shear stress changes given by [:I] Au = 1.33 s, In I, + o$,[l (ocR/~)] (Mayne and Bachus 1988) It is important to note that Au = (u u,) in [I] corresponds to the excess pore-water pressure obtained with elements positioned behind the cone tip, since significantly different results are obtained from the cone tip or face (Mayne et al. 1990). By also representing the cone tip resistance (q,) in terms of a cavity expansion formulation, I, can be effectively removed from the equation. Using the expression given by VesiC (1977), the net cone resistance becomes [2] qt ov0 = su[1.33 (lnI, + 1) + 7r/2 + 11 If the relationship between undrained strength ratio (s,,/o$,) and OCR from modified Cam Clay (Wroth 1984) is adopted with A = 0.75, then [l] and [2] may be combined to give where M = 6 sin $'/(3 sin 6' ). Although this simplified approach does not include the influence of strength anisotropy, initial stress state, stress rotation, strain rate, soil fabric, and other important considerations, [3] appears to