Processes such as pile penetration and cyclic loading cause a loss of soil strength, some of which is recovered through re-consolidation and thixotropic strength gain. In this study, the remolded strength and the thixotropic strength recovery will be measured in Gulf of Mexico (GoM) clay using two techniques: the full-flow penetrometer (cyclic T-bar) and the miniature vane shear test. Most of the previous studies were limited to 60 days of time of curing. Therefore, this study extended the cure period to 114 days to fill the existing gap in long-term measurements of thixotropic strength recovery in this clay. The results show that the gain in strength due to thixotropy effect under a long time period was about 0 to 30% during the first day and it continues to increase sharply to about ∼ 80 % after prolonged periods of time. This study adds to the database evaluating the gain in shear strength under prolonged time using different types of testing at different depths for Gulf of Mexico clay.
As defined by Mitchell (1960), thixotropy is an isothermal, reversible, time dependent process where a material stiffens while at rest softens or liquefies upon remolding. Thixotropy refers to time-dependent strength gain in soil at constant water content after remolding. This process is in contrast to the strength gain in soil associated with consolidation, which occurs under conditions of changing water content. There are multiple factors affecting the strength of the soil (e.g. Plasticity index (Ip), Sensitivity of the soil (St), Activity of the soil (Ac), etc.). Fig. 1a shows some examples of a measured thixotropy strength ratio with different plasticity index and different type of soils which are kaolin, Bentonite, and Gulf of Mexico clay. The thixotropy strength ratio can be defined as the ratio of the gain in undrained shear strength with time (su_t) to remolded undrained shear strength (sur). It shows how the gain in strength differs depending on the soil properties. Thixotropy is considered as a significant factor for offshore geotechnical design (e.g. subsea structures, anchoring systems, piles, etc.).
