The crucial interaction between lessons learned from the study of unsaturated soil mechanics and energy geotechnics was highlighted at the recent third edition of the International Symposium on Energy Geotechnics (SEG23), held in Delft, the Netherlands. This short communication summarises the discussion that revolved around handling the many issues raised by the current energy transition from fossil fuels to more sustainable and renewable resources, and the need to integrate unsaturated soil knowledge into energy geotechnics. The panel discussion at the symposium emphasised how crucial it is to use the fundamental concepts of unsaturated soil mechanics for a range of energy applications to be able to characterise key underlying multi-phase processes and enable efficient design. With representatives from around the world, the panel discussion's goal was to close the gap between theoretical research and real-world applications by fostering a dialogue between academics and industry, thereby advancing creative and sustainable geotechnical solutions. The understandings generated from this conversation highlighted the necessity of ongoing cooperation and knowledge sharing to propel area developments and successfully address the urgent energy and environmental challenges of our time.

It is clear that to address climate change, an energy transition which makes a large-scale use of the subsurface is needed. The subsurface will play a critical role in this transition, serving as a resource for new sources of energy production and storage, a foundation for energy infrastructure, and a repository for waste by-products from energy production (e.g., radioactive waste disposal, CO2 geo-sequestration). Furthermore, there are challenges in understanding material behaviour due to complex coupled phenomena, measuring material properties and upscaling the physical phenomena to engineering scale structures. Uncertainties, heterogeneities and long timescales offer additional challenges, as does bringing technology ever closer to dense populations. This is the topic of Energy Geotechnics. In the next decade and decades, society needs to complete the energy transition, and to do so the already substantial changes need to be vastly accelerated. This brings many challenges, which academics, consultants, contractors and authorities need to address together. [...]