Pressure infiltration characteristics of bentonite slurry affected by the salty water: experimental study and mechanistic understanding

The pressure infiltration of fresh and salty bentonite slurries against a medium-fine sand has been investigated in a laboratory setup. In the tests, two series of salty bentonite slurries were used: non-pre-hydrated salty slurry, for exploring what will happen if directly salty water is used to make bentonite slurry, and pre-hydrated salty slurry, for identifying the consequence of pre-hydrated fresh bentonite slurry mixing with the salty water in the soil pores. The salty water employed was a mixture of different percentages of freshwater and seawater. Experimental results show that the test with non-pre-hydrated salty slurry exhibited a significantly faster and shorter (time) mud spurt, or even no mud spurt at all, compared to the test with fresh or pre-hydrated salty slurry. The influence of salty water on the pre-hydrated fresh bentonite is less than on the non-pre-hydrated slurry and depends on the seawater content in the salty water. Compared with the test with fresh bentonite slurry, a slower and shorter (time) mud spurt could be seen in the test with the pre-hydrated salty slurry when the seawater content was not more than 20%. As seawater content exceeded 20%, a faster mud spurt showed up; however, the timespan of the mud spurt may be shorter or longer, mainly depending on the viscosity and sedimentation behavior of the bentonite. A model to estimate the slurry infiltration distance during mud spurt is introduced, which agrees well with the experimental results using the measured input parameters. After the mud spurt, a filter cake would form in each test. The permeability of the filter cake increased with the increase in seawater content. Directly mixing salty water remarkably increased the permeability of the filter cake, while the pre-hydration of bentonite could reduce this increase. For instance, with the salty water containing 10% seawater, the permeabilities of the filter cakes formed by fresh bentonite slurry, non-pre-hydrated salty slurry, and pre-hydrated salty slurry with the 50 g/L bentonite concentration were 1.69 × 10⁻⁹ m/s, 2.26 × 10⁻⁸ m/s, and 3.23 × 10⁻⁹ m/s, respectively.