Infrastructure systems are the connective tissue of advanced societies. Besides the crucial role that they play for communities worldwide, they stand out for the sheer amounts of materials required for construction and maintenance. Most of these resources derive from the subsurface, thus rendering the role of geotechnical engineers essential to meet the goals of global sustainable development. The 11 letters included in this issue reflect in disparate ways the increasingly strategic role that the geotechnical community plays in the sustainability landscape. Specifically, they offer a glimpse of how engineering ingenuity can open unexpected avenues to discover new materials, valorise waste, and maximise the effectiveness of geostructures.
An essential line of inquiry in the domain of sustainable infrastructures is the ability to move beyond the established practices through design innovations that foster an efficient use of all the components of a subsurface system. The paper by Gunawan et al. (2025) falls within this broad theme by offering new perspectives on how to account for the interaction among soil, pile groups and raft foundations, thus countering the common tendency for the over-conservative design of these systems. By providing simple and readily available design tools, this paper highlights how the consideration of previously unaccounted interactions can be harnessed to achieve improved performance and a more efficient use of materials. The letter by Zhang et al. (2025a) tackles a similar challenge, i.e., the optimization of non-standard systems such as sliding mudmat foundations for energy recovery in submarine settings. In this work, with the guidance of finite element analyses, readily available empirical expressions are proposed to quantify the bearing capacity in the presence of highly heterogeneous site conditions.
A similar angle emerges from the paper by Bellezza and Fratalocchi (2025), who derived analytical solutions quantifying the stress transfer between unstable ground and an embedded free-head flexible pile. This type of advances empowers engineers with new methods to optimise the rigidity of subsurface systems and, consequently, their design. The benefits of analytical modelling are also displayed in the contribution by Gao et al. (2025), who examined the complex dynamic interactions between tunnels subjected to extreme events, such as subterranean blasts, and the surrounding saturated, anisotropic ground deposits. Both studies encourage a deeper reflection on an important, but often forgotten, trend of engineering design: its increasing reliance on computationally intensive models. Much like materials, however, computational power is also a scarce resource. Under this perspective, computationally inexpensive, time-efficient analytical solutions stand out as a crucial asset to guide their comprehension of subsurface processes and their related design endeavours.
The subsurface is not only a domain where engineered systems are installed. In many circumstances, it is also the most abundant and readily accessible basin of construction materials. The contribution by Mosallanezhad and Sadat Taghavi (2025) brings this fact into the context of mechanically stabilised earth, a technology that for decades has represented a cost-effective and environmentally friendly solution for infrastructure systems. By documenting new measurements from large-scale pullout tests, the authors propose an innovative strategy to enhance the frictional capacity of steel strip reinforcements, which relies on the insertion of readily deployable twisted members, thus further encouraging the use of this class of sustainable geotechnical infrastructures.
Geotechnical innovation in the realm of sustainable design comes in many forms and at all length scales. One not to be sidelined is the scale of the engineered materials of which most subsurface systems are made. Both the letters by Lopes et al. (2025) and Yao et al. (2025) address this theme. Lopes et al. (2025) explore an innovative application of microbial-induced calcium carbonate precipitation for erosion control in transportation infrastructure. This solution not only reduces the need for traditional cementitious materials by facilitating spontaneous calcium carbonate precipitation, but it also offers a new way to consume CO2 by stimulating bio-weathering, a process which holds potential to activate carbon-negative effects that in the future may turn infrastructures into major carbon sinks. Along similar lines, Yao et al. (2025) proposes innovative solutions for compacted soil liners which deploy biochar to improve the characteristics of naturally occurring residual soils commonly used in landfill construction. Their study shows that by alleviating the risk of cracking, biochar enhancement represents an effective solution to enhance the durability of waste containment facilities and improve their long-term performance, with obvious benefits for society in terms of reduced maintenance and lower remediation costs. Shifting into the domain of deep underground geotechnical applications, the contribution by Zhang et al. (2025b) provides a detailed multi-scale depiction of the degradation of a fine-grained rock, such as a siltstone, subjected to drying-wetting cycles. With the support of a sophisticated combination of multi-modal measurements, this work indicates that the propagation of damage during hydrologic cycles is governed by the breakup of mineral particles, which modulates internal friction and can significantly accelerate fatigue failure.
Still centred on the endeavour of properly managing the by-products of human activities is the letter by So et al. (2025), which discusses the feasibility of valorising abundant construction waste (CW) to replace sand blankets as drainage layers for earthen structures. Their findings show that, if properly optimised, CW can guarantee hydraulic conductivity at least ten times greater than that of typical sand. Such an identification of alternatives to traditional sand blankets is not to be underestimated, in that it is rooted in the principles of circular economy and mitigates the possible risk of natural sand over-exploitation that plagues coastal cities with high population growth. Waste, however, is not always a resource. Rather, in many circumstances, it is a threat for communities and ecosystems. This is the case of mining residues, commonly referred to as tailings. The letter by Patiño et al. (2025) addressed this subject through the laboratory characterisation of non-plastic copper ore tailings from a seismically active region in Spain. Their findings provide insight into the unique dynamic behaviour of these materials, thus contributing to new solutions to quantify their spatial variability, improve their storage practices, and ultimately mitigate their threats.
A further essential factor involved in understanding how to regulate the mechanics of geotechnical materials and optimise their performance is the multi-scale interaction among their constituents. Several contributions tackled this broad theme through a combination of computational and experimental methods. Specifically, the letter by Covilla et al. (2025) examines the process of void ratio redistribution during undrained shearing in a Malaysian kaolin, revealing that, although the global void ratio of the specimens is unchanged, shearing leads to significant local alterations of both the porosity and the pore pressure fields. These results emphasise the limitations of model calibration relying solely on elemental tests and the significance of spatial heterogeneity for geomaterial characterisation. The crucial role of pore pressure heterogeneity is also at the core of the letter by Chao et al. (2025). In their work, the authors developed a novel fibre-optic sensor able to provide local measurements of pore water pressure within soil specimens. By offering significant advantages in terms of increased data acquisition frequency and reduced response time, this new technique not only addresses several limitations of existing measurement systems, but it also improves our ability to effectively track the development of hydro-mechanical inhomogeneities within deformed soil specimens. Along similar lines, the paper by Kinslev et al. (2025) examines with innovative non-destructive techniques how re-sedimentation is responsible for non-negligible hetherogeneity in fine-grained soils, such as silts and clays. In particular, nuclear magnetic resonance conducted at sub-millimetric scale has revealed that, while particle sorting in fine-grained soils cannot be ruled out, fabric heterogeneity plays a dominant role, and must be carefully considered during sub-sampling procedures aimed at subsequent stages of post-sedimentation characterisation. Finally, by transitioning into the realm of granular materials, the contribution by Xue et al. (2025) tackles the onset of non-homogeneous strain fields (e.g. shear bands), a quintessential factor for the assessment of the ultimate capacity of geotechnical systems. By using insight from Discrete Element Model simulations, this paper emphasises how the geometric features of such strain localisation zones emerge from particle-scale interactions, thus providing new tools to constrain the parameters of a non-local continuum model and facilitate scalable numerical solutions for subsurface systems.
The letters collected in this issue collectively exemplify how sustainable design can be pursued in many forms and enacted across all the length scales relevant for geotechnical systems, from particles to specimens and geostructures. Such connotation is a further reason why advances at each of these length scales are worth being pursued, in that even specific contributions that successfully optimise the workflow of geotechnical design, construction, and maintenance readily compound across scales, eventually leading to transformative achievements for local communities, the global economy, and society at large.
