Experimental study on rheological behaviors of Na-bentonite slurries under seawater intrusion

Abstract

During the construction of submarine tunnels, the phenomenon that the seawater contaminates slurries is inevitably encountered. This will lead to obvious deterioration in rheological properties of the slurry, and even cause tunnel face instability. This study aimed to identify the constitutive relationship and rheological characteristics of slurries under seawater intrusion using laboratory experiments. Carboxymethyl cellulose (CMC) was selected as the effective additive to slurries in this paper. Mixtures of Na-bentonite slurries, CMC, and seawater in different ratios were prepared. The viscosity, flow curve, rheological model and physical stability of slurry samples were studied. Furthermore, the viscosity enhancement mechanisms of additives in freshwater and seawater slurries were also investigated. The results show that the increase of CMC and Na-bentonite contents can both greatly enhance the viscosity and make the shear-thinning behavior of slurries more obvious. The exponential equation and linear equation can be used to describe the growing relationships between the yield stress of slurries and the contents of Na-bentonite and CMC, respectively. In addition, the accuracy of the Bingham model predictions in the flow pattern of freshwater slurries was reduced when the viscosity was relatively high. At this time, the constitutive relationship can be better described by the Herschel-Bulkley model. Moreover, seawater intrusion significantly deteriorated the rheology and physical stability and changed the flow pattern of slurries. CMC played a more obvious role in altering the rheological model and increasing viscosities of slurries mixed with less seawater, which can effectively alleviate the deterioration in rheological behavior and maintain physical stability. Microscopically, CMC can make agglomerations more compact and continuous due to the formation of hydrogen bonds with bentonite particles, thus guaranteeing the swelling of bentonite particles and maintaining the excellent rheological properties of slurries contaminated by seawater. This research can provide significant guidance for the establishment of slurry infiltration theories and numerical models under seawater intrusion.