Reusing Fine Silty Sand Excavated from Slurry Shield Tunnels as a Sustainable Raw Material for Synchronous Grouting

Using the Nanjing Dinghuaimen Yangtze River Tunnel project as a case study, we proposed a method to reuse the excavated silty-fine sand by adjusting the proportion of the waste sand to replace the commercial sand. This would address the issue of recycling the significant amount of waste sand generated when the slurry shield passes through the silty-fine sand stratum. Moreover, we have evaluated grout indicators such as density, fluidity, consistency, bleeding rate, volumetric shrinkage, setting time, and unconfined compressive strength and examined how the particle size and distribution of the sand affected the grout's performance. The findings show that as the replacement ratio increases, the grout's density, fluidity, consistency, and bleeding rate gradually increase; meanwhile, the volumetric shrinkage increases initially before decreasing; the setting time decreases gradually; the unconfined compressive strength initially decreases before increasing. The key factor altering the grout's performance when the replacement ratio is less than 50% is the weakening of the adsorption effect of fine sand particles on water due to the increase in the sand's fineness modulus. When it is greater than 50%, the particle size of the sand tends to be distributed nonuniformly and fine particles fill the voids between larger particles, thus contributing to the changes in grout properties.

Automated summary

Using the case study of the Nanjing Dinghuaimen Yangtze River Tunnel project, a method was proposed to reuse excavated silty-fine sand by adjusting the waste sand proportion to replace commercial sand. This addresses the issue of recycling the substantial amount of waste sand generated during the slurry shield passing through the silty-fine sand stratum. Various grout indicators and the impact of sand particle size and distribution on grout performance were evaluated. The findings reveal that increasing the replacement ratio gradually improves grout density, fluidity, consistency, and bleeding rate, while volumetric shrinkage initially increases before decreasing, and the setting time decreases gradually before unconfined compressive strength initially decreases and then increases. The critical factor that influences grout performance when the replacement ratio is below 50% is the weakening adsorption effect of fine sand particles on water due to the increase in sand fineness modulus. When the replacement ratio surpasses 50%, the nonuniform distribution of sand particle size and the filling of voids by fine particles between larger particles contribute to changes in grout properties.