EPB-TBM performance enhancement through cutterhead modification in Shiraz Metro Line 3

• Hybrid cutterhead configuration—featuring double disc cutters, precut rippers, and button rippers—achieved a 3.2 times increase in cutter life compared to reference benchmarks. • Geological data was used to inform tool layout decisions, supported by a lightweight 1R classifier with 81.25% predictive accuracy. • Monthly advance rate reached 215 m, placing the SM3 TBM performance in the 79th percentile among global EPB tunneling projects. • Normalized thrust and torque were reduced by 36% and 52%, respectively, demonstrating significant energy efficiency gains. • Findings offer a replicable framework for cutterhead adaptation in mixed ground urban tunneling conditions. This study evaluates the performance outcomes of cutterhead modifications applied to an Earth Pressure Balance Tunnel Boring Machine (EPB‑TBM) during excavation of Shiraz Metro Line 3 (SM3). The alignment traversed complex mixed ground conditions—primarily clayey soils (65%) with segments of coarse alluvium and bouldery zones—necessitating a hybrid cutting tool configuration and reduced cutter spacing (from 100 mm to 50 mm). The modified cutterhead incorporated double disc cutters, intermediate precut rippers, and peripheral button rippers to enhance wear resistance and tool lifespan, with tool selection guided by geological condition (GC) and optimized using a 1R rule‑based classifier that achieved 81.25% accuracy and confirmed GC as the dominant predictor. Additional interventions included adjusting installation heights and realigning cutting tools to reduce off‑axis loads, which contributed to extended cutter life and improved soil fragmentation. Performance benchmarks demonstrated significant gains, with penetration rate averaging 39 mm/min (peak 70 mm/min), monthly advance reaching 215 m (79th percentile globally), cutter life improving to 2105 m³ per Primary Cutter Type (PCT)—3.2 times reference values—and torque and thrust reduced by 52% and 36%, respectively, while penetration per revolution increased by 18%. Correlations between normalized torque/thrust and cutter life, verified through SM3 and Similar Case Study (SCS) datasets, confirmed a decreasing power‑law relationship governed by tool configuration, highlighting the innovation of integrating hybrid cutterhead design with normalized performance indicators and lightweight classification to provide a practical framework for EPB‑TBM deployment in heterogeneous urban geology.