Mechanical properties and microstructure of lime-treated shield tunnel muck improved with carbide slag and soda residue.

Shield tunnel muck are usually discarded due to high water content and poor engineering properties, resulting in occupation of land sources and waste of soil sources. Meanwhile, large amounts of industrial waste such as carbide slag (CS) and soda residue (SR) are landfilled with a low reuse rate, which poses a threat to the natural environment. This study aims to improve waste shield tunnel muck using CS and SR and traditional lime, and the improved tunnel muck is expected to be used in subgrade filling to provide a new approach to solve this dilemma. A series of physical, mechanical, subgrade property, and microcosmic tests were conducted on shield tunnel muck improved by CS, SR and lime. The effects of different mixing proportions on the properties of improved tunnel muck were examined. The micro-improvement mechanisms of CS and SR on tunnel muck were explored. Results indicate that the addition of CS or SR can effectively improve the physical and mechanical properties of shield tunnel muck. CS plays a significantly role than SR in improving physical and mechanical properties of tunnel muck. A synergistic enhancement is observed as the combined CS and SR are added, and the optimal mixing proportion of tunnel muck to CS to SR is found to be 100:6:2 with a fixed lime content of 4 %. The alkaline environment created by the synergistic action of CS and SR promotes the dissolution of the active ions in soils, and the generated crystals and gelling products of hydration significant contribute to soil improvement. The tunnel muck improved with appropriate CS or SR content could meet the requirements for light or medium traffic load levels and can be effectively utilized as subgrade filling. • Carbide slag or soda residue enhances tunnel muck's properties significantly. • Mechanical properties plateau in tunnel muck beyond 6 % carbide slag content. • Combined carbide slag and soda residue has a synergistic enhancement. • Optimal mix: tunnel muck, carbide slag, soda residue (100:6:2) with fixed 4 % lime. • Carbide slag / soda residue - enhanced tunnel muck meets subgrade performance norms. [ABSTRACT FROM AUTHOR]