Sustainability of Micropiles and Conventional Deep Foundations: A Critical Review and Performance-Equivalent Assessment Framework

Deep foundation construction presents significant sustainability challenges due to its reliance on carbon-intensive materials, energy-consuming installation processes, and associated environmental disturbance. Micropiles have emerged as an alternative to conventional driven, bored, and continuous flight auger piles, particularly in restricted-access construction and foundation rehabilitation. However, existing comparisons often emphasise structural performance, initial costs, or individual environmental indicators without adequately considering whole-life sustainability. This critical narrative review examines the engineering, environmental, and economic performance of micropiles relative to conventional deep foundation systems. It evaluates structural characteristics, material consumption, embodied carbon, construction efficiency, environmental disturbance, durability, and life-cycle costs. The synthesis highlights important trade-offs, including the installation flexibility and reduced ground disturbance associated with micropiles against their reinforcement requirements, grout consumption, and potentially intensive drilling operations. Methodological inconsistencies involving functional units, assessment boundaries, and project-specific assumptions further complicate sustainability comparisons. To address these limitations, the review proposes an integrated, performance-based sustainability assessment framework combining structural adequacy, environmental impacts, economic feasibility, site constraints, and long-term performance. The framework emphasizes context-dependent, performance-equivalent comparisons rather than assuming the superiority of any foundation technology. This approach provides a basis for evidence-informed foundation selection, improved environmental assessment, and more sustainable infrastructure development.