Application of a novel grouting material for prereinforcement of shield tunnelling adjacent to existing piles in a soft soil area

Abstract

During urban subway construction, it is inevitable that shield tunnels will pass under the piles of existing structures or buildings. To minimize the adverse effects of shield tunneling on existing piles and structures, grouting is commonly used to prereinforce the surrounding soil. In this paper, a new grouting material (CSGSA) is proposed for prereinforcement of shield tunneling adjacent to existing piles. CSGSA uses bulk solid waste (i.e., slag powder and desulfurized gypsum) and cement as the main raw materials, and a self-developed activator is added as a catalyst and improves the stability and strength of the grout. The impacts of ingredients and the formulation on the performance of the CSGSA grout were investigated. The optimal formula ratios for the specific gravity of slag powder slurry, cement, gypsum and activator are 1.30 to 1.35, 50%, 25% and 1.5%, and these were determined with a battery of testing methods. The microcosmic mechanism for functioning of the optimal CSGSA was analyzed with XRD and SEM, and the results showed that both a pozzolanic effect and filling effect are observed. The applicability of the CSGSA was validated through a field engineering case involving prereinforcement of shield tunneling adjacent to existing piles in soft soil areas, and the findings indicated that the CSGSA material satisfied the project needs in a low-cost and eco-friendly manner.