Experimental Study of Tunnel Invert Construction Using 3D Concrete Printing (2024-09)¶

Application of 3D concrete printing (3DCP) in tunnel invert construction presents a solution to the challenges inherent in conventional methods. This study proposes using 3DCP for tunnel invert construction to improve productivity. This method can reduce the number of concrete workers from six to two, a 67% reduction. This paper reports on two experiments testing the proposed method. The first experiment tested the shape accuracy of a mock-up arch of the tunnel invert. The mock-up member was constructed by printing a grid-shaped permanent formwork (3DCP-formwork) and pouring concrete into it. The shape of the mock-up member was measured using 3D scanning, and the shape accuracy of the lateral surface of the 3DCP-formwork met the specification requirements. The 3DCP-formwork also aided in the uniform finishing of the top curved surface. The second experiment examined the mechanical integrity of hybrid sections consisting of a 3D-printed component and internal concrete. Hybrid specimens with different printing patterns (straight and staggered) and plain concrete specimens were prepared for flexural and compressive strength tests. In the flexural strength tests, the staggered printing pattern improved mechanical integrity and exhibited greater flexural strength than plain concrete with a vertical joint, a known weakness in conventional construction. In the compressive strength tests, the compressive strengths of the straight and staggered printing patterns were 36% and 44% higher than that of plain concrete, respectively, indicating good mechanical integrity.