Formulation and performance of grouting materials for underwater shield tunnel construction in karst ground

•A new hardened cement-bentonite grouting material (HCBGM) for underwater karst cavern was proposed.•Effects of compositions on performances of the HCBGM are investigated.•Optimal formulation of HCBGM for karst cavern with groundwater flow was determined.•The technique, cost and eco effectiveness of the HCBGM was verified by an field case study. Grouting is one of most important techniques for underwater tunnelling in karst ground which is actually difficult to be resolved due to the presence of underground water flow. This paper proposed a new grouting material to fill karst caverns when there is flowing underground water prior to shield tunnel construction. The grout uses bentonite and cement as the base material, and a curing agent were added to form excellent fluidity, stability and scour resistance. The effects of the composition and formulation on the performance of the grouting material, and the optimal formulations were determined through a series of laboratory experiments. The recommended parameters for the grout are a specific gravity for the bentonite slurry from 1.30 to 1.35, a cement content of 30%, a meta-aluminate content of 1.25% and a lignin content of 0.20%. The effectiveness of the hardened cement-bentonite grouting material (HCBGM) was checked by a field grouting application for a underwater shield tunneling in karst area, and the results illustrated that the proposed grouting material not only can fulfill the engineering requirements but also turns out cost effective and eco-friendly.