Multiple Thixotropisms of Liquid Limit–Consistency Clays Unraveled by Multiscale Experimentation: Fid-Bau Portal

Multiple Thixotropisms of Liquid Limit–Consistency Clays Unraveled by Multiscale Experimentation

Peng, Jing / Luo, Shengmin / Wang, Dongfang / Cao, Yiming / DeGroot, Don J. / Zhang, Guoping

Multiscale experiments were conducted to investigate the thixotropic behavior of a naturally occurring illite-rich marine clay with a moderate salinity and of a manufactured, highly purified kaolin clay at respective liquid limits. The temporal evolution in undrained shear strength $s_{u}$ and small-strain shear modulus $G_{\max}$ was assessed using fall cone and bender element testing, and one-dimensional X-ray diffraction and electron microscopy were employed to probe microfabric changes. Results showed that both the $s_{u}$ and $G_{\max}$ of the two very soft clays exhibited a time-dependent increase by as much as 330% and 386% over $\sim 64 days$ , respectively, which can be divided into two stages with drastically different rates: a much higher rate during the initial 2–7 days, and a lower rate over extended time. Such a transition in the hardening rate manifested dissimilar thixotropic mechanisms dominating the two stages; whereas the initial stage is controlled by fabric aging chiefly dictating $s_{u}$ , including particle rearrangements (e.g., reorientation, aggregation, and flocculation) and homogenization of defects and disturbance, the later stage is controlled by contact aging dominating the long-term increase in $G_{\max}$ . A temporal increase in both the $s_{u}$ and $G_{\max}$ fit the three-unit Burgers model well, further confirming that multiple mechanisms contribute to different thixotropic stages with dissimilar rates.