Spray-Based 3D Printed Tunnel Lining Concrete (2026-03)¶

The intelligent and full-angle construction of tunnel lining critically depends on the anti-sagging performance of concrete. This study proposes a full-angle printing path optimization method, which explicitly accounts for the anti-sagging behavior of spray-based 3D (S-3D) printed concrete. The time-dependent effects of different accelerator dosages (0-6%) on the interfacial bonding tensile and shear strength of fresh-existing concrete are investigated within 30 min. An analytical model is subsequently developed to predict the anti-sagging thickness of S-3D printed concrete. Guided by the model, a printing path for the full-scale tunnel model (measuring 7.4 m in height, 8.8 m in width, and 24 m in arc length) is designed and validated. The results demonstrate that the interfacial bonding strength increases linearly, and its growth rate shows a positive correlation with accelerator dosage. Furthermore, the interfacial bonding shear strength is significantly greater than the tensile strength, which contributes to the superior anti-sagging performance in the 90° printing compared to the 180° printing. The analysis of full-angle anti-sagging thickness provides a basis for the precise control of key parameters (printing area, layer thickness, deposition sequence) in the printing path. The printing domain is divided into 12 zones, which are fabricated printed sequentially from zone 1 to zone 12. Under this path, the real-time anti-sagging stability coefficient remains above 1.0, and construction efficiency is improved by 56.1% compared to the conventional method. Finally, a 30 cm thick lining structure is successfully printed within 60 min, which further validates the effectiveness of the proposed method.