Effect of pre-shearing on the steady and dynamic rheological properties of marine sediments

Marine sediments can exhibit complex rheological behaviour particularly thixotropic character due to the presence of organic matter/biopolymer. Such biopolymers can lead towards the development of multiple length scale flocculated structures which are sensitive to the shearing level and history. In this study, extent and rate of structural recovery was examined in marine sediments by measuring storage modulus as a function of time using small amplitude oscillatory tests after the destructive steady shearing. This linear viscoelastic response of the sediments was further investigated as a function of several parameters including shearing level, shearing time, measuring geometry, temperature, sediments density, and oscillation frequency. Rate of structural build-up in sediments was estimated by fitting the experimental data to the stretched exponential function, in order to analyse the effect of above mentioned factors on the extent and recovery rate of the structure. Moreover, a structural parameter (λ) was also defined based on the storage modulus before and after shearing, with the aim of linking the structural level of the sediments with the rheological properties such as yield stresses. The results showed that the recovery of structure after shearing was instantaneous, however, the extent of recovery was highly dependent on the studied parameters. The extent of recovery was maximum for the samples with highest density and lowest organic matter content. The effect of shearing time on the extent and rate of structural recovery was almost negligible whereas by using vane geometry the extent of recovery was higher than the Couette geometry. Yield stresses showed a strong dependency on the structural parameter (λ) of the sediments, however, this effect became negligible by decreasing the structural parameter after certain value. This study provides an extensive understanding about the structural recovery in marine sediments under different shearing conditions which can be useful for ports and waterways applications.