THE RATE OF SWELLING OF OVERCONSOLIDATED CLAYS SUBJECTED TO UNLOADING

Time-rate of swelling under one-dimensional drainage and either one-dimensional or isotropic deformation conditions was investigated using reconstituted specimens of Duck Creek. Crab Orchard, Cucaracha aid Bearpaw shales. Cylindrical specimens were used, drainage was allowed from the top, and pore water pressure was measured at the base of all specimens. Load-deformation-history variables included maximum pressure (80 psi, 500 psi and 1500 psi), overconsolidation ratio (1.07–250), decrement ratio (0·07–15·7), and sustained secondary swelling (up to 3 log time cycles). The swelling index, Cs, is a function of the overconsolidation ratio, OCR. Cs, changes with effective stress and the rate of excess negative pore pressure dissipation is very sensitive to the changes. Secondary swelling can be very sig nificant. The ratio of secondary swelling index, Cas, to Cs, can be as high as 0·4. The maximum value of 0·4 for Cas/Cc, contrasts with the maximum observed value of 0·1 for Cα/cs, for consolidation. However, ...