Observed uplift behaviors of segmental lining during shield tunneling in hard rock: a case study from Changsha, China

• Published in: Tunnelling and underground space technology 2024-08, Vol.150, p.105816, Article 105816
• Main Authors: Wu, Huai-Na, Xu, Xiao-Peng, Chen, Ren-Peng, Liu, Yuan, Cheng, Hong-Zhan, Xiao, Chao
• Format: Article
• Language: English
• Subjects: Field measurement; Joint deformation; Longitudinal deformation; Longitudinal stress relaxation; Transverse deformation; Tunnel uplift
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2024.105816

To explore the development law of tunnel uplift during tunnelling in hard rock and its inherent relationship with the deformation of segmental rings and bolt force, this study carried out field measurements on the deformation and mechanical behaviors of shield tunnel during construction based on the North Extension Project of Changsha Metro Line 1. Five monitoring items were conducted in field measurements, including tunnel uplift, the dislocation between segmental rings, circumferential joint opening, lining circumferential and longitudinal strains, and longitudinal bolt axial force. The measured results indicated distinct stages of tunnel uplift, including the initial rapid uplift stage (Stage I), the relatively gradual uplift stage (Stage II), the second rapid uplift stage (Stage III), and the final stable stage (Stage IV). The uplift was more significant in the location of 4∼8 rings away from the shield tail, and it took approximately 40∼65 hours to be stabilized after detachment from the shield tail. The process of uplift was influenced by factors such as the buoyancy of bedrock fissure water and unsolidified slurry, grouting pressure, and the interaction between the segmental rings. Meanwhile, a notable synchronization between the transverse deformation of the tunnel, dislocation between segmental rings, circumferential joint opening, longitudinal bolt axial force, and the development of tunnel uplift was observed. The flattening effect caused by longitudinal differential deformation of the tunnel resulted in a “horizontal elliptical” shape of the tunnel cross-section. During the process of tunnel uplift, the maximum dislocation between segmental rings was reached, which gradually recovered with the stability of the uplift. Notably, the monitoring conducted over three months after construction confirmed a continuous increase in both the circumferential joint opening and the longitudinal bolt axial force at corresponding locations, providing evidence of longitudinal stress relaxation in the tunnel. Additionally, the curved section of the tunnel showed a trend of recovering toward the inner side of the curve.