In response to current climate considerations, the geotechnical sector is increasingly exploring multiphysical approaches to develop sustainable engineering projects. This thesis focuses on two promising applications that combine the sector's decarbonisation objectives with geomechanical functionality: energy geostructures and biocementation. Multiphysical modelling has played a key role in their development and remains an essential tool to advance innovation adoption.

For energy geostructures, modelling and design frameworks are well established. The remaining challenge is to extend the domain of application beyond its well-known uses, primarily energy pile foundations in balanced climates, and demonstrate their effectiveness in alternative scenarios. In contrast, modelling frameworks for biocementation are often not validated at the large scale. Upscaling also continues to pose challenges, and recommendations for overcoming these are not readily available. These problems obstruct the step towards design principles.

In this setting, the thesis has a twofold objective: (i) to extend the range of applications for energy geostructures by moving beyond conventional considerations and (ii) to move towards developing design approaches for biocementation treatment. By building on existing knowledge and using multiphysical modelling as a central tool, the research offers new insights into the design, optimisation, and application of these technologies and aims to support future sustainable geotechnics.

Numerical analyses are used to look at three different settings for the application of energy geostructures. The potential of energy piles to provide cooling energy in hot-dominated climates is demonstrated through simulations, which show that, despite unbalanced thermal demands, temperatures stabilise over time and respect heat pump limitations. Simulations reveal that geothermal activation of an underground data centre can reduce internal air temperatures, and this effect can be used to optimise ventilation system performance but requires a case-by-case evaluation. Finally, models are used to understand the internal air dynamics of an energy metro station, and recommendations are provided for how such factors can be accounted for in its design. These works demonstrate that through modelling, the technology can be optimised to maximise its impact in providing renewable thermal energy.

The work then demonstrates how multiphysical modelling can aid in achieving standardisation of biocementation. A modelling framework is benchmarked against upscaling experiments to assess its performance. Recommendations for achieving homogeneity in biocementation soil improvement are provided, highlighting the benefits of using high, consistent injection rates and demonstrating the effect of using novel injection geometries. The framework is then adapted to simulate treatments using an ex situ hydrolysis method, revealing a shift in the governing precipitation mechanism from urea hydrolysis to calcium carbonate precipitation kinetics in relation to mixing patterns. Last, the effects of different treatment configurations for slope stabilisation via biocementation are analysed using both limit equilibrium and finite element methods. While biocementation can improve slope stability, its success largely depends on the manner of application. These findings highlight the contribution of modelling in developing effective approaches for biocementation treatment.