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.

Massive shield tunnel muck is being landfilled without effective use due to high moisture contents and poor engineering properties, which not only leads to soil resources waste, but also occupies a large amounts of land sources. In this study, industrial waste phosphogypsum (PG) was recycled to improve the tunnel muck with lime, and the improved muck is aiming to be used in subgrade filling. A series of laboratory tests, including compaction tests, unconfined compressive strength (UCS) tests, california bearing ratio (CBR) tests, resilient modulus tests and microscopic tests were carried out. The effects of PG, lime, carboxymethyl cellulose (CMC) and moisture contents on physical, mechanical and microscopic properties of improved muck were examined, respectively. Results indicate that the incorporation of lime and PG significantly improves the mechanical properties and water stability of shield tunnel muck generated in silt stratum. The performance of improved tunnel muck meets the requirement for subgrade filling. Notably, for a fixed total contents of lime and PG, the proportion of 3:1 lime/PG results in the best mechanical properties and water stability. The tunnel muck generated in silt stratum mainly consists of lamellar and layered structures, which contributes to stronger cohesion among soil particles and the hydration products. The CMC has the ability to create cementation bonds among soil particles and the hydration products of lime and PG, resulting in a denser gel network microstructure.