Thin shell foundations: Quantification of embodied carbon reduction through materially efficient geometry

Building foundation systems are a significant but understudied contributor to embodied carbon emissions of the built environment, and typically use excess material in prismatic, bending-dominated typologies. This paper identifies and characterizes a promising pathway for reducing the embodied carbon associated with reinforced concrete shallow foundations through an alternative typology, thin shell foundations. The main focus is a quantification and comparison of the environmental impact of typical spread footings and materially efficient shell foundations. Validated analytical engineering equations are applied in a parametric design workflow for the same design load and soil bearing capacity. By iterating through this workflow systematically, insights are gained regarding the applicability of shell foundations to various building typologies and site conditions. Results show that for small column loads and weak soils, shells reduce embodied carbon by about half compared to spread footings. For high applied loads, shells significantly outperform their prismatic counterparts, reducing the environmental impact by almost two-thirds. Foundations are then considered within the context of a whole building structural frame to determine the potential downstream savings when multiple systems are optimized to reduce material use and mass. When floor slabs are shape-optimized in addition to using shell foundations, a building structural system can be constructed for nearly one-quarter of the embodied carbon of a typical system. To take advantage of these potential savings, a method for fabricating thin shell foundations, where earth is compacted and milled to create the formwork, is presented following a review of digital fabrication methods.