Life cycle assessment of an underground car park's retaining walls

Abstract In 2020, the construction sector contributed to 37 % of global CO 2 e emissions. While efforts have primarily targeted reducing environmental impacts related to building operations through enhanced energy efficiency, the significance of addressing embodied impacts (arising from materials/products) has recently garnered attention. Underground car parks (UCPs) mitigate the scarcity of parking space in densely urbanized regions, though they pose unique design and construction challenges not encountered in above‐ground structures. This paper seeks to compare the environmental performance of retaining walls within the excavation pit of an UCP associated with an office building in Berlin, Germany, over a service life of 50 years through a life cycle assessment (LCA). Four structural alternatives are evaluated: (a) permanent steel sheet pile, (b) temporary steel sheet pile with a permanent reinforced concrete wall, (c) permanent concrete secant pile, and (d) permanent concrete diaphragm wall. Utilizing the life‐cycle framework outlined by EN 15798, the LCA encompasses the product stage, construction process, repair, end‐of‐life, and benefits and loads beyond the system boundary. Predominantly based on environmental product declarations in accordance with EN 15804+A2, the LCA meets ISO 14044 requirements and has successfully undergone critical review by an independent panel comprising three German experts.