Quantitative evaluation of thixotropy-governed microfabric evolution in soft clays

Thixotropy-governed temporal microfabric evolution, in a naturally occurring illitic marine clay and a manufactured kaolinitic clay at their respective liquid limits, was probed quantitatively by both one-dimensional X-ray diffraction (1DXRD) and 2DXRD via orientation index (OI) and texture index (TI) respectively. Results showed that the two fabric indexes, OI and TI, continuously evolved nonmonotonically but consistently during the thixotropic hardening periods of up to 125 days. Due to the initial remolding-induced large-strain shearing, both clays started with a fabric consisting of highly parallel-oriented clay particles. With increasing time, the OI varied from 23.1 to 36.6 and from 3.8 to 4.5, while their TI ranged from1.004 to 1.008 and 1.010 to 1.029 for the kaolinitic and illitic clays, respectively. Moreover, the same trend of changes between the OI and TI for both clays indicated that the two XRD-based techniques are applicable to characterizing the temporal microfabric changes in soft clays undergoing thixotropic hardening. The fabric evolution may result from various microscale particle rearrangements, likely including clay particle reorientation, aggregation, and flocculation, which in turn are controlled by interparticle forces. The two XRD-based techniques are also discussed in terms of their advantages and can expectedly shed light on similar studies of time-dependent behavior of soft clays.