Integration of groundwater by-pass facilities in the bottom slab design for large underground structures

- Groundwater barrier effect and bottom slab are mitigated by an integrated design.
- The original and integrated designs are compared numerically.
- Designs are tested for three scenarios in which the groundwater conditions are modified.
- The integrated design allows reducing the costs and increasing the safety.

The impacts induced by the interaction between underground constructions and groundwater should be minimised by implementing corrective measures. These impacts are twofold, which means that underground constructions affect groundwater, and vice versa. Two common situations resulting from this interaction are the barrier effect (impact of an underground construction on groundwater) and groundwater pressure on the bottom slab (impact of groundwater on an underground construction). In the literature, there are examples and designs of mitigation measures to minimise both impacts. However, to the best of the authors' knowledge, there are not any designs that combine corrective measures to minimise these simultaneously. This paper proposes an innovative groundwater by-pass design to mitigate the barrier effect and to alleviate the groundwater pressure on the bottom slab. The proposed integrated design was applied to the largest underground infrastructure in Barcelona: the Sagrera railway station. The design was tested and compared numerically with a solution initially designed (not integrated). The numerical comparison was undertaken with three different hydrogeological scenarios. The proposed integrated design mitigated the barrier effect and optimised the bottom slab. It considerably reduced costs and increased safety during the construction phase.