Primary and secondary compression behavior of Florida organic soils

A comprehensive laboratory investigation was conducted to evaluate the primary and secondary compression behavior of undisturbed organic silts and peats obtained from 11 locations along SR 15/US 98 in Palm Beach County, Florida. A total of 43 consolidation tests were performed. The primary objectives were as follows: (i) to conduct a series of standard consolidation tests to determine the Compression Index, Cc, and the Coefficient of Consolidation, cnu; (ii) to determine the Secondary Compression Index, Calpha, at stress levels (sigmanu'/sigmap') ranging from 0.30 to 1.15; and (iii) to employ the well-known Time-Stress-Compressibility concept to establish a unique relationship between C alpha and Cc. It was found that for all practical purposes, the Calpha/C c ratio at any stress level is 0.03, which is consistent with the values reported in the literature for similar soils. A constant Calpha/Cc ratio provides an approximation of Calpha once C c is determined from a standard consolidation test, and without the need of ongoing laboratory testing to predict long-term settlement.