Optimization of Grouting Material for Shield Tunnel Antifloating in Full-Face Rock Stratum in Nanchang Metro Construction in China

Grouting control is one of the key measures to reduce segment floating, to ensure safety and efficiency during shield tunnel construction. In this study, optimization of backfill synchronous grouting material for shield tunnel antifloating in the water-rich full-face rock stratum in Nanchang Metro Line 4 is conducted based on laboratory experiments and in situ application. First, orthogonal tests are designed and conducted to investigate the influence of four main factors, that is, water-binder ratio, binder-sand ratio, cement-fly ash ratio, and bentonite-water ratio, on grouting material properties. Based on this, optimization is proposed using response surface methodology combined with laboratory optimization tests. According to the optimization, an admixture mass proportion (bentonite: 11.81%, hydroxyethyl methylcellulose: 0.42%, nanosilicon: 0.7%) is chosen based on the original grouting material constituents and then verified through both laboratory and field tests. The results show that the optimization can significantly increase the setting time, 1-d unconfined compressive strength, and water-land strength ratio, reducing almost 36% of the uplifting value of the tunnel segment when water-rich full-face rock stratum is encountered in this case.