Higher hard rock proportions accompany lower penetration and greater specific energy in an ultralarge slurry shield case study

Abstract Quantifying excavation performance and cutter condition is essential for ultra-large-diameter slurry shields operating in upper-soft and lower-hard composite ground. This study combines 512 ring-level construction records, excavation-face composition for the initial 66 rings, and seven cutter inspections from a 16.15-m-diameter slurry shield. Mechanical excavation power from cutterhead rotation and shield propulsion, penetration per revolution, and mechanical specific excavation energy (MSEE) were evaluated alongside a disc-cutter adaptation of the Overall Service Health Condition (OSHC) framework using radial wear and valid inspected counts. The hard-rock face area ratio was negatively correlated with penetration per revolution (Spearman’s ρ = −0.633) and positively correlated with MSEE ( ρ = 0.692). From Stage I to Stage III, mean penetration per revolution increased from 3.73 to 11.23 mm/rev, while mean MSEE decreased from 7.82 to 2.60 kWh/m 3 . Cutter inspections revealed pronounced radial differences in wear. At the seventh inspection at Ring 302, the damage-oriented coefficients for front cutters, edge cutters and the inspected population were 0.757, 0.964 and 0.833, respectively, with larger values indicating greater damage. The combined framework distinguishes mechanical loading from volume-normalized excavation performance and identifies edge cutters as a maintenance priority in composite-ground tunnelling.