Study on structural performance and safety enhancement of ECC tunnel linings: Experimental and numerical investigations

To address the critical challenges of high brittleness, pronounced cracking susceptibility, and defect-induced damage in conventional concrete tunnel linings, this study fabricated 30 engineered cementitious composite (ECC) lining specimens and conducted systematic loading tests. The effects of key design parameters-namely, cover thickness (2 mm, 4 mm, and 6 mm), reinforcement ratio (0%, 0.8%, and 1.6%), and defect-induced damage-on the structural performance of ECC linings were comprehensively investigated. Experimental results indicate that increasing both the cover thickness and reinforcement ratio significantly alters the failure mode, with higher reinforcement ratios promoting a transition from crushing failure to ductile failure. The load-displacement curves of ECC linings exhibit four distinct stages: elastic, yielding, strain-hardening, and a gently descending branch, thereby overcoming the inherent brittle failure characteristic of ordinary concrete. The confining effect provided by external reinforcement outperforms that of internal reinforcement. When the cover thickness is 4 mm and the reinforcement ratio is 1.6%, the interfacial confinement coefficient reaches 0.85, while the lining safety factor exceeds the prescribed code requirement. An ECC lining model was developed based on the nonlinear constitutive relationship of ECC, with numerical predictions for peak load, elastic stiffness, and crack width showing errors below 6.7%. The finite element model, which accounts for eccentricity and initial defect-induced damage, accurately reproduces the entire deformation and failure process of ECC linings. Compared with ordinary concrete, the compressive and tensile safety factors of full-scale ECC linings across various sections are increased by 29.4%–65.9% and 48.4%–75.0%, respectively. Moreover, ECC linings exhibit pronounced deformation warning signs prior to structural failure, implying lower engineering risks. This study provides reliable design recommendations for ECC lining structures.