National Gallery of Ireland
An additional basement level was constructed beneath the National Gallery on Merrion Square in Dublin. The construction work includes underpinning the existing load bearing walls of the building to facilitate the construction of a new subterranean plant room below the building and also the construction of a new energy centre which will front onto Merrion Square. The concrete underpins were constructed in 1m wide panels using a sequential series of excavations, concreting and dry-packing. The National Gallery Building is a structure of national importance and therefore the settlement tolerances for the building during underpinning works were very strict.
GDG was commissioned by IGSL to undertake a finite element analysis to determine the magnitude of the settlements during construction of the underpins. Both (i) the long-term settlement following completion of the underpinning and (ii) the incremental settlements due to the staged nature of the underpin panels was required.
Scope of Work:
GDG completed detailed non-linear finite element modelling (FEM) of the underpinning beneath the National Gallery in Dublin in order to determine the likely settlements.
The scope of work for the GDG analysis is outlined below:
- A ground model was developed to simulate the in-situ soil stratification based on SI reports and investigations carried out to date. This included interpretation of geophysical data.
- It was agreed that a single worst-case superstructure load case would be considered based on analysis of the load combinations and basement foundation geometry.
- The ground model was calibrated using published literature which was combined with available site investigation information for the site and the surrounding area.
- The pre-construction loads were simulated on the existing foundations to generate an in-situ stress state in the soil.
- The under-pinning excavation was then simulated by re-distributing the load onto the adjacent layers.
- The settlement analysis considered the additional incremental settlement that may occur due to load redistribution as the underpinning is being carried out, as per the suggested underpin construction sequence.
- In addition to the incremental settlements during construction, the analysis also determined the total settlements after the underpinning is complete.