Evaluating Deep and Shallow Metro Station Structures Through BIM-LCA and Spatiotemporal Disruption Analysis

Subterranean metro stations require substantial structural material inputs and can generate prolonged disruption in dense urban environments. Rather than assessing the environmental performance of an entire metro system, this study compares the embodied environmental impacts and surface-occupation effects of two representative underground station typologies from the Istanbul M7 Metro Line: a deep Top-Down station and a shallower Cut-and-Cover station. The proposed SECURE framework integrates Building Information Modelling (BIM)-based Life Cycle Assessment (LCA) with a Spatiotemporal Disruption Index (SDI), which is used as a physical proxy for cumulative surface occupation during construction. The assessment covers material production, transport, end-of-life processes, and recovery benefits in accordance with ISO 14040/14044, while excluding operational energy and on-site construction machinery from the comparative LCA boundary. The results show that the deep Top-Down typology requires 3.11 m3/m2 of structural concrete, compared with 2.22 m3/m2 for the Cut-and-Cover typology. Within the analysed cases, this higher structural material intensity is associated with a 54% increase in Global Warming Potential, from 9953.62 to 15,343.14 kg CO2 eq/m2. The difference primarily reflects the combined influence of excavation depth, station geometry, reinforced concrete volume, and permanent retaining elements, rather than the construction sequence alone. In contrast, the Top-Down typology substantially reduces modelled surface occupation, with cumulative SDI decreasing from 115,800 to 45,675 m2·month. These findings indicate a trade-off between embodied environmental burden and potential socio-spatial disruption. The study therefore suggests that early-stage metro station planning should evaluate excavation depth, structural mass, construction sequence, and surface continuity together. For deep urban stations where Top-Down construction is required, low-carbon cement substitution and localised material sourcing may help reduce material-related environmental impacts.