Mechanical Behavior of Double-shell Structure with Different Positions of Inner Lining Defects

To examine the impact of inner lining defects on the mechanical behavior of double-shell structures and validate the efficacy of the shield tunnel support system, similar model tests were employed to analyze the deformation characteristics, internal force distribution, damage progression, and interaction strength of double-shell lining structures with inner lining defects in three typical locations (crown, shoulder and waist) under ultimate loads. This study discloses how inner lining defects affect the load-bearing capacity of the double-shell structure and makes recommendations. The results show that (1) The existence of defects in the inner lining makes the deformation of the double-shell lining structure under the action of external loads uncoordinated. The overall load-bearing capacity of the structure decreases by 33% to 50%. (2) Local stress concentrations and increased eccentricity lead to a significant increase in the internal force proportion and failure of the defective inner lining, thus failing to limit the deformation of the segments and the early damage of the double-shell lining structure. (3) Of the three locations studied, the impact of inner lining defect position on the mechanical behavior of the double-shell structure follows this ranking: arch waist most impactful, crown weaker than arch waist, least impactful at shoulder.