Reliability-Based Service-Life Assessment of Slotted Rockbolts in Chloride-Rich Underground Mines: Coupled Uniform–Pitting Corrosion and Time-Dependent Anchorage Degradation

Corrosion-induced degradation of steel rock reinforcement poses a major risk to the long-term stability of underground roadways, particularly in coastal mines where groundwater is chloride-rich and frequently acidic to near-neutral. Slotted (friction) rockbolts are especially vulnerable because their capacity depends on tube ring stiffness and steel–rock friction, both of which deteriorate with wall-thickness loss and localized damage. This paper proposes a reliability-based service-life assessment framework for slotted rockbolts that couples a time-dependent anchorage model with a conservative representation of localized pitting corrosion. Generalized corrosion is modeled as thickness reduction governed by an uncertain penetration rate, while pitting is incorporated through an equivalent penetration amplification factor acting at the controlling cross section, enabling straightforward probabilistic evaluation. The framework defines a time-dependent limit state in terms of anchoring capacity relative to a required support threshold and evaluates failure probability and time-to-threshold metrics via Monte Carlo propagation of uncertainty in corrosion kinetics, pitting severity, interface friction, rock–bolt interaction stiffness, and installation variability. A demonstration for a coastal chloride-rich mine scenario shows that pitting can reduce predicted safe service life by factors of approximately 2–5 under moderate localized attack and approach order-of-magnitude reductions under severe pitting compared with uniform-loss-only predictions. Geometry sensitivity results indicate that increasing wall thickness is the most effective design lever for extending service life, followed by radius reduction, while increases in bolt length exhibit diminishing returns once the transfer length is exceeded. The proposed approach provides a practical, risk-informed basis for friction-bolt selection, maintenance planning, and remaining-life prediction in aggressive underground corrosion environments.