Design of Anti-blocking and Anti-seepage shield grouting materials and their performance enhancement mechanism analysis

Abstract

To solve the current problems of long-distance pumping blockage and poor stability of shield grouting material in the construction of subway tunnels, we studied the effects of thickener and water reducing type, dosage, and water-to-binder (W/B) ratio on the workability and mechanical properties of shield grouting materials with high-volume crushed sand and ultrafine powder. The mechanism of thickeners' effects on improving mortar properties was analyzed using the cryo-scanning electron microscopy (Cryo-SEM). The results show that proper compatibility of components and proportion optimization make it possible to prepare high-performance shield grouting materials with excellent anti-blocking and anti-seepage properties. These materials exhibit high fluidity, low pressure bleeding rate, homogeneous distribution of components, and meet the engineering requirements regarding setting time and strength of grouting material. A comparison of the performance of three types of thickening agents reveals that although hydroxypropyl methylcellulose (HPMC) improves the pressure bleeding rate of mortar significantly compared to seaweed gum, it leads to a significant delay in the setting time and a decrease in mortar strength. Welan gum (WG) has a minor impact on grouting materials' setting time and strength, and its water retention performance is similar to that of HPMC. However, WG is expensive and causes significant fluidity loss of slurry over time. On the other hand, seaweed gum demonstrates comprehensive advantages in enhancing various aspects of shield grouting materials, exhibiting good anti-blocking and anti-seepage effects. For its calcium-induced gelation property, seaweed gum forms an orderly screen structure of an “egg-box” shape in the pore liquid, then fills the pores between the screens through the film effect of the gel. Finally, the gels form a “screen-printing-like” overall effect, so that seaweed gum has the three-dimensional space network effect as WG and the film forming effect as that of HPMC, which can significantly improve the stability of the grouting material. Therefore, seaweed gum has almost no adverse impact on the strength of shield grouting material but has a relatively lower price.