Spray-based 3D printed foam concrete: Stress concentration relieve utilization

This study employs spray-based 3D (S-3D) printed foam concrete to propose a design method for tunnel yielding support, addressing the issue of concentrated stress failure in lining structures under large deformation surrounding rock. The mechanical performance of concrete under concentrated compressive stress is evaluated with varying thicknesses of the S-3D printed foam concrete layer (15, 25, 35, and 45 mm). The yielding protection mechanism of the S-3D printed foam concrete layer is analyzed based on its effects on concrete bearing capacity, failure morphology, and deformation energy absorption. The results demonstrate that S-3D printed foam concrete effectively mitigates concentrated stress. Compared to cast concrete, S-3D printed foam concrete exhibits superior synergy with the foundation structure. At a thickness of 15 mm, the S-3D printed composite structure (S-15) exhibits typical yielding support characteristics, transitioning from single-crack to multi-crack failure modes. Relative to the control group (C-0), the ultimate compressive load, ultimate deformation, and energy absorption capacity of S-15 increase by 31.6 %, 243.5 %, and 331.8 %, respectively. To further assess the capacity of S-3D printed foam concrete to alleviate concentrated stress under more complex stress states , shear tests are conducted on SS-15. Compared to the control group (CS-0), the ultimate load, ultimate deformation, and energy absorption capacity of SS-15 improved by 32.2 %, 135.1 %, and 145.7 %, respectively. The findings confirm that S-3D printed foam concrete effectively reduces the concentrated stress exerted by rock on tunnel lining structures and enhances the long-term support performance. • S-3D printed foam concrete can work as a tunnel-yielding support layer. • S-3D printed foam concrete can relieve concentrated stress for concrete structure. • Concentrated stress test is designed to verify the yielding support performance. • Optimal printed foam concrete improves 145.7 % energy absorption capacity.