Optimization of shield tunnel joints: Focusing on structural performance with considerations for low-carbon emissions and economic efficiency

• Single row sleeve joint (SRSJ) achieves 97% of cast iron joint (CIJ)’s load-bearing capacity with improved sustainability. • Double row sleeve joint (DRSJ) bolts experience the highest stress and variability, indicating significant stress concentration. • SRSJ and DRSJ all demonstrated lower embodied carbon and costs compared to CIJ, with reductions of up to 7.21% in emissions and 6.42% in costs. Optimizing shield tunnel joints is essential to meet the evolving demands of modern construction, where balancing structural performance, environmental impact, and cost efficiency is increasingly important. Traditional cast iron joint (CIJ) has been widely used, but there remains significant room for improvement in terms of both their mechanical efficiency and sustainability. This study addresses these challenges by investigating two alternative designs: the single row sleeve joint (SRSJ) and the double row sleeve joint (DRSJ). The research focuses on evaluating their mechanical performance and potential to reduce carbon emissions and costs, offering a more comprehensive and future-forward solution compared to the traditional CIJ. Through experimental testing, key performance factors such as joint deflection, rotational angle, concrete strain, and bolt strain were analyzed alongside joint toughness, ductility, cracking patterns, embodied carbon, and material cost. Key findings revealed that SRSJ achieved 97% of CIJ’s ultimate bearing capacity, while DRSJ reached only 75%. In the elastic phase, SRSJ performed significantly better, supporting twice the load of CIJ. Bolt strain analysis showed that DRSJ experienced greater stress concentration, while SRSJ maintained balanced strain distribution. SRSJ also outperformed CIJ and DRSJ in toughness and ductility, particularly in rotational flexibility, exceeding CIJ by 76%. SRSJ and DRSJ all demonstrated lower embodied carbon and costs compared to CIJ, with reductions of up to 7.21% in emissions and 6.42% in costs. Overall, SRSJ emerged as a viable alternative, balancing mechanical performance, sustainability, and cost efficiency. In contrast, DRSJ’s stress concentration issues limited its effectiveness, making it less advantageous compared to CIJ.