Experimental study on creep behavior in oedometer tests of reconstituted soft clays

The creep behavior of soft clays is essential in evaluating the long-term deformation of foundations. Because this behavior of naturally deposited clays is very complex as a result of their structures, loading history, and physicochemical processes, in addition to the heavy workload and high cost for the sampling procedure of natural soft clays, oedometer creep tests were usually conducted on reconstituted clays, aiming to establish the fundamental work for the elastic-viscoplastic modeling (EVP) and the creep prediction of natural soft clays. In this study, based on a series of one-dimensional creep tests of reconstituted soft clays, the relationship between the creep coefficient (C α ) and the vertical effective stress (σ' v ) and that between C α and the ratio of vertical effective stress to preyielding stress (σ ' v /σ ' y ) are presented in semilogarithmic planes. The results suggest that the C α value increases with the vertical effective stress prior to reaching the threshold stress (σ2.17σ ' y ), and then C α gradually decreases after it. The results (C α vs. compression index C c ) show that the statistical C α /Cc value of reconstituted clays ranges from 0.015 to 0.05, which is more than that of natural soft clays (0.03-0.05). This suggests that the reconstitution process is beneficial to restrain the creep of soils. Furthermore, it was found that the C α /C c value of reconstituted clays linearly decreased with the void ratio when vertical effective stress exceeded the threshold stress (~2.17σ ' y ). Based on the data of this study and data from previous studies, a prediction equation for Ca after the threshold stress is proposed, showing that C α is a function of the void ratio and the void ratio at the liquid limit.