Abstract：To resolve the problems of screw conveyor spewing and obstruction of excavated debris during EPB shield tunneling in the water-rich sandy stratum, new chemical additives were developed based on the adaptability of soil conditioning agents for different stratum, and relevant laboratory tests were carried out. The test results show that the non-ionic polymerized foam agent has both foaming and stabilizing properties. An appropriate increase of foaming agent concentration (cf) can increase the foaming expansion rate (FER) and half-life time (HT). However, when cf exceeds 5%, FER and HT tend to reach the maximum value at the critical micelle concentration. The transmission electron microscope (TEM) test results show that the new liquid spewing-preventive agent has chain structures, and the purpose of spewing prevention through the adsorption and wrapping of fine-grained soil by the long-chain structure of the polymer can be realized. The test results of conditioned soil show that the slump of conditioned sandy soil increases with the increase of foam injection ratio (FIR) and spewing-preventive agent injection ratio (PIR), and decreases with the increase of bentonite injection ratio (BIR). When FIR=40%, BIR=20% and PIR=20%, the permeability coefficient of the conditioned soil is three orders of magnitude lower than that of the unconditioned soil. A three-dimensional digital microscope system was used to analyze the microstructure of different conditioned soil. The results show that the foam morphology changes from sphere to polygon with time. The clay particles in Bentonite may reduce the porosity of the coarse-grained soil. The spewing-preventive agent congregates the soil particles of different sizes together with water molecules to reduce the permeability of the conditioned soil. Additionally, the screw conveyor spewing prevention technology in water-rich sandy stratum is put forward combined with many shield tunnel projects, so that the successful excavating-through of the tunnels can be ensured.
