Experimental study on infiltration behavior of slurry containing excavated sand into saturated sand

This research investigates the infiltration patterns of a bentonite-sand slurry into saturated sand. Bentonite-sand slurry is formed when excavated sand mixes with bentonite slurry inside the excavation chamber, a common phenomenon during slurry shield tunneling. Employing a normal laboratory setup designed to emulate field conditions, the study elucidates the impacts of varying bentonite and sand concentrations, as well as the pressure applied, on the infiltration process. The findings highlight that low-permeability zone invariably form on the sand layer's surface, with their formation rate and pressure transfer efficiency being negatively influenced by the sand particle accumulation from the slurry. The infiltration process, as dictated by changes in the Peclet number (Pe), can be effectively categorized into three distinct stages: mud spurt, internal filter cake formation, and surface filtration. The correlation between the duration of the first two stages and the sand content can be described by a linear function. It was observed that low-permeability zone formation can be expedited, and slurry pressure transfer can be enhanced, by increasing the concentration of bentonite. The manipulation of excess slurry pressure, however, produced inconsistent outcomes, as increased applied pressure was found to lower pressure transmission efficiency. Mechanisms of bentonite-sand-slurry infiltration are discussed, and implications for field applications are described.