Research on reuse of silty fine sand in backfill grouting material and optimization of backfill grouting material proportions

Abstract

Silty fine sand is a common muck in shallow urban tunnels, and the reuse of on-site muck resources is an urgent need in the field of shield tunneling. A shield tunneling section of Nanjing Metro Line 7 in a silty fine sand formation was analyzed in this paper. Combined with SPSS multiple regression analysis and MATLAB multiobjective planning tools, X-ray diffraction technology and laboratory tests were used to optimize the ratio of muck grouting liquid. The feasibility of silty fine sand as a substitute sand source for backfill grouting liquid was discussed. Based on actual conditions, the influences of grout performance and grouting parameters on the diffusion of the grouting liquid in the seepage stage were studied. The effectiveness of the muck grout was verified by monitoring values such as surface settlement and segment uplift in the field test. The results showed that silty fine sand can be used as the sand source for preparing grouting liquid that meets the requirements of on-site construction through the addition of a water-reducing agent and by optimizing the ratio. The grouting liquid with the best performance has advantages in terms of 7 d and 28 d strength, bleeding rate, and cementation strength. The stability of this grouting liquid is good, and 44.6% of costs can be saved; the cost-optimized ratio grouting liquid has advantages in 7 d strength and economic benefit, and 74.6% of costs can be saved. However, the stability of this grouting liquid is poor. Under the same grouting time, the pressure generated by the muck grouting liquid and the field grouting liquid on the unit area of the segment is close.