Infiltration characteristic of modified slurry and support efficiency of filter cake in silty sand strata

To improve the understanding of infiltration characteristic of modified slurry and the support efficiency of filter cake in silty sand strata, the slurry infiltration (SI) and filter cake formation (FCF) were investigated in a laboratory apparatus. The water discharge and the excess pore pressure at different depths of silty sand strata were measured during SI. The relationship between permeability coefficient/thickness ratio of filter cake (kc/L) and effective slurry pressure conversion rate of filter cake (n) were analyzed. Moreover, the SI and FCF process as well as the modification mechanism of CMC (carboxymethyl cellulose) were clarified. The experimental results indicate the formation of only external filter cake in the silty sand strata. The slurry particles obtain thicker water membrane after being modified by CMC, which blocks partial water path in filter cake and decreases the water discharge significantly. The silty sand excavated from tunnel face also contributes to the water discharge reduction. The kc of the external filter cake ranges from 3.83X10-8 cm/s to 7.44X10-8 cm/s. The n of the external filter cake is over 96%, which decreases with increasing kc/L. A silty sand content within 10% is suggested during construction to ensure the uniformity of the filter cake.