Abstract: The utilization of tunnel shield muck for the preparation of backfill grouting materials presents a viable strategy for enhancing resource recycling and achieving carbon reduction goals in shield tunnelling. This study employs waste sands and mucks generated during shield construction in the NanchangTianxiang Avenue Tunnel along with locally sourced steel slag (SS), as primary raw materials. An orthogonal experimental design is applied to optimize the mix proportions of the grouts, examining the effects of SS substitution rate, superplasticizer dosage, and muck content on key performance parameters such as grout fluidity and 28-day compressive strength. Micro-structural analyses, including X-ray diffraction and scanning electron microscopy, are conducted to investigate the phase composition, morphology, and hydration characteristics of hardened grouts at various curing ages. Experimental results indicate that a mix with 20% SS replacement rate, 5% superplasticizer dosage, and 30% muck content yields an initial fluidity of 215 mm and a 28-day compressive strength of 4.6 MPa. The determined optimal mix ratio is cement : fly ash : SS : shield waste sand : muck : bentonite : superplasticizer : water = 130 : 200 : 50 : 630 : 270 : 100 :6.4 : 600. The grout prepared with this formulation demonstrates low bleeding and shrinkage rates, meeting the engineering requirements for backfill grouting applications. Hydration analysis reveals that the synergistic effect of SS hydration and the pozzolanic reaction of fly ash promotes the formation of more ettringite and C-S-H gel, which effectively fills internal voids and enhances the bonding strength of the interfacial transition zone. Consequently, a significant improvement in compressive strength at 28 days is achieved.