Experimental Study on the Mix Proportion and Mechanical Properties of New Underwater Cementitious Filling Materials

Considering that it is difficult for traditional materials to simultaneously meet the requirements for filling grouting of water-filled karst caves and subsequent shield tunneling, an environmentally friendly and controllable new underwater cementitious filling material (NUC-FM) is developed, with abandoned shield mud as the basic raw material. Through laboratory tests, the mechanical property parameters of NUC-FM are tested, and its micromechanism is analyzed. The research results show that there is excellent synergistic interactions among shield mud, cement, flocculant, fly ash and other raw materials. The NUC-FM grouting filling material with superior performance can be prepared when the water binder ratio is between 0.45 and 0.6 and the water consumption is between 270 and 310 kg/m³. It has the characteristics of non-dispersion underwater and moderate consolidated body strength. The compressive strength of the NUC-FM consolidated body samples under each mix proportion is much higher than 0.5 MPa, which meets the technical strength requirements of a construction site, and the microstructure shows that there is an obvious dense and stable block structure inside. The cost of the NUC-FM prepared with an optimized mix proportion is only 34.57 dollars/m³, which is far lower than the market purchase price of concrete and cement mortar. It can be predicted that the NUC-FM is an ideal filling grouting material for water-filled karst caves in shield tunnels in water-rich karst areas.