Research on reuse of shield muck on backfill material for prefabricated metro station fat slots and its application

The resource utilization of shield muck has been widely investigated for synchronous grouting and flowable stabilized materials; however, its application to confined and irregular fat slots in prefabricated metro stations remains insufficiently studied. In this study, a shield muck-based cementitious backfill material (SM-SCBM) incorporating shield muck and recycled crushed stone was developed for this application. An L 25 orthogonal design was used to evaluate the effects of water-to-cement ratio ( W / C ), cement-to-stone ratio ( C / St ), and stone-to-muck ratio ( St / M ) on fresh-state properties and compressive strength. The optimized mixture achieved a slump of 142 mm, a bleeding rate of 2.71%, a stone retention rate of 98.05%, and a 28-day compressive strength of 28.67 MPa. SEM and FTIR analyses indicated that improved particle packing and hydration-product formation contributed to a relatively dense particle binder structure. An in situ comparative test at Huaxia Station of Shenzhen Metro Line 6 showed that, compared with conventional C20 concrete, the SM-SCBM section exhibited smaller post-construction fluctuations in shear-key axial force, suggesting a more gradual early-stage stress redistribution. Life-cycle assessment further indicated an 36.39% reduction in carbon emissions and a cost saving of approximately 190 yuan/m 3 relative to C20 concrete. These results demonstrate the feasibility of SM-SCBM as a low-carbon backfill material for confined prefabricated metro-station fat slots.