Unified Thrust–Torque Assessment of Jamming Risk for Double-Shield TBMs in Squeezing Ground

TBM jamming in deep, weak, squeezing ground poses a persistent threat to construction safety and schedule performance. Most existing approaches evaluate shield jamming and cutterhead jamming independently, even though TBM operation is simultaneously limited by the available thrust and torque capacities. This study proposes a unified thrust–torque assessment framework that integrates the time-dependent response of weak surrounding rock, represented by the Cvisc model, with interface-based rock–TBM contact. The framework was applied to a representative Himalayan tunnel excavated by a double-shield TBM. The calculated total tunnelling resistance and cutterhead torque demand were then evaluated against the corresponding rated machine capacities. A parametric investigation covering advance rates of 0.5–2.5 m/h, over-excavation amounts of 3–9 cm, shield lengths of 12–16.5 m, and surrounding-rock elastic moduli of 2–8 GPa identified advance rate as the dominant controllable factor, contributing 61.6% of the variance in total tunnelling resistance and 96.2% of that in cutterhead torque. Increasing the over-excavation amount primarily alleviated shield–rock contact and reduced shield frictional resistance by up to 56.2%, while exerting only a limited influence on cutterhead torque. These findings were subsequently synthesised into a project-specific jamming-risk zoning matrix, which identified low advance rates combined with small over-excavation under long-shield conditions as the most unfavourable operating regime. Field validation was conducted using 10 representative operating cases satisfying η < 0.9. The calculated responses agreed well with the monitoring data, yielding R2 = 0.82 and a MAPE of 12.0% for total tunnelling resistance versus field-monitored thrust, and R2 = 0.72 and a MAPE of 16.3% for cutterhead torque. The proposed framework therefore provides a quantitative basis for TBM parameter selection and jamming-risk control in squeezing ground within the validated operating range.