Editorial: Integral bridges: advancing resilient and sustainable designs Free

Integral bridges are preferred in modern transport infrastructure due to their robust, jointless configuration, which enhances durability and reduces maintenance requirements and cost compared with conventional jointed bridges (Caristo et al., 2018). By eliminating bearings and expansion joints, they offer significant long-term advantages in terms of cost efficiency, safety and service continuity. However, these same attributes introduce new design complexities, particularly regarding soil–structure interaction (SSI), thermal effects and long-term structural behaviour.

As our transport infrastructure demands shift towards resilience and sustainability, integral bridges represent an important opportunity – but also a design challenge. Resilience in this context refers not only to structural robustness under cyclic and extreme loads but also to the system’s ability to absorb and adapt to environmental and operational changes over time. Meanwhile, sustainability demands design solutions that reduce embodied carbon dioxide, optimise materials and minimise whole-life impacts.

This themed issue explores these intersecting challenges through a set of studies. The included papers tackle critical issues such as strain ratcheting in backfill soil, the influence of compaction variability, modelling refinements to soil pressure estimation and the integration of novel detailing and experimental validation. Together, they demonstrate how advancing our understanding of integral bridge behaviour – both structurally and geotechnically – can help build infrastructure that is not only technically sound but also more resilient to disruption and sustainable over its lifecycle.

The paper by de La Cuesta Padilla et al. (2025) provides an in-depth design case study of the Nant Ffrwd mainline bridges in South Wales, featuring 70 m long integral structures with 19 m tall abutments. It introduces a practical refinement to the calculation of enhanced earth pressures (K*) by iteratively accounting for abutment flexibility and soil stiffness. This methodology led to a 58% reduction in estimated earth pressures and substantial material savings, demonstrating how thoughtful calibration against real structural stiffness can enhance both economy and sustainability of integral bridge design.

Morley et al. (2025) explore the ratcheting mechanism of soil behind integral abutments using centrifuge modelling (Figure 1). Their experimental campaign successfully simulated the behaviour of backfill under cyclic thermal loading and evaluated how different configurations – soil density, abutment flexibility and foundation fixity – affect stress build-up. Notably, they confirm that stiffer abutments mobilise deeper soil pressures, while flexible systems concentrate earth pressures closer to the surface. Their findings challenge oversimplified design assumptions and reinforce the importance of advanced physical modelling in refining design standards, including parametric studies that can support the use and structural efficiency of integral bridges towards more resilient transport networks.

Bennison et al. (2025) examine a complex integral and semi-integral bridge system built on continuous secant piled walls. The study tackles challenges arising from skewed configurations and groundwater ingress. A novel semi-integral detailing approach is proposed to manage water ingress and reduce soil pressures at the back of abutments. Additionally, the authors demonstrate the effectiveness of non-linear springs (derived from geotechnical models) in structural analysis, showing good agreement with traditional iterative SSI methods. This proposal streamlines the SSI modelling process and has direct implications for more efficient future designs.

Finally, Laaksonen and Mäntyranta (2025) present experimental findings from the integral bridge simulator, focusing on the impact of soil compaction ratios and flexible materials on the response of stub-type end screens. Their tests showed that higher compaction ratios lead to stiffer responses and higher mobilised pressures, while compressible layers such as geofoam can reduce strain ratcheting and promote displacement symmetry. The experimental results were cross-validated with long-term monitoring data from a Finnish bridge, offering valuable insight into how lab-scale results translate to field conditions.

This themed issue showcases the breadth of challenges and innovations shaping the design of integral bridges. From empirical and centrifuge-based validations to iterative and non-linear modelling strategies, the collected works underscore a key message: SSI must be understood as a coupled, dynamic process rather than a static approximation.

As bridge designs continue to evolve in complexity – spanning longer distances, coping with more aggressive environments and aiming for carbon efficiency – the insights presented here provide both a foundation and a forward-looking vision. We hope these contributions inform practitioners and inspire further research to refine the safe, sustainable and cost-effective use of integral bridge systems.