The Paper has stimulated the writer to comment on the soil structure changes that take place with strain and with time. The writer considers two concepts here (a) the important differences in time effects when drainage is allowed during strain (b) the contribution of permanent soil structure change during secondary aging to the increase in the clay preconsolidation yield point, i.e. to the quasi-preconsolidation effect.The writer considers that the Authors' exclusive use of undrained testing to measure time rate effects in the mobilization of clay shear strength constitutes an important limitation to the conclusions they can extract from their test results. Figure 4 of the Paper gives seven examples of the linear decrease in undrained strength with the log of strain rate, with 0.003% per hour the smallest rate shown. For the purpose of discussion, imagine carrying the Fig. 4 trends for undrained shear to extremely small strain rates. These trends suggest that no clay could reach a stable equilibrium condition (approximately zero strain rate) because its strength would diminish to nearly zero. This contradicts what is known about real clay behaviour, namely that aging usually tends to increase clay strength and helps the clay to attain a stable condition in the field. Why this contradiction? The answer probably involves the drainage that can take place in conjunction with very low strain rates. The writer proposes that how shear strength varies due to different strain rate may depend on the drainage that can take place during the shear strain.Consider the aforementioned 0.003% per hour rate in Fig. 4 of the Paper: the writer judges that most clays strained at that rate or less, or 14 or more days for each 1% compression, would do so under at least significantly partially drained, and perhaps even essentially fully drained conditions. This would almost certainly be the case for laboratory triaxial specimens of ordinary size and with ordinary 433 boundary drainage conditions. By considering strain-rate effects in the direction of low rates of strain, the writer believes that clay strength behaviour in the field may differ greatly from the undrained test results reported by the Authors, not only in magnitude but also in the direction of strain-rate effects. The following is some laboratory test evidence to support this. Figure 1 shows the comparative results from a series of drained compression tests on machine extruded, duplicate specimens of kaolinite, tested in an identical manner with the same equipment with only strain rate varied (Schmertmann & Hall, 1962; Schmertmann, 1982). The writer allowed drainage and controlled pore pressures in all these tests such that they strained at the same constant value of major principal effective stress, or'. The top part of Fig. 1 shows the deviator stress against strain curves obtained using a constant u,'= 3.30, after isotropic normal consolidation to (T,' = 3.50 kg/cm'. It can be seen that the mobilized shear resistance of this drained clay increased with reduced strain r...

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