Observations of ground and structure movements during site redevelopment in Dublin

An extensive monitoring system was installed to provide data on the behaviour of some retained masonry façades and on ground movements, resulting from basement excavation, during the redevelopment of a prestigious site in Dublin. Observations made by electrolevel beam sensors have implications for future façade retention system design. They revealed a thermally induced daily cyclic movement of the retained façades, which was partially irrecoverable. This resulted in permanent total deformations of up to 100 mm. An extended archaeological dig exacerbated the situation. The masonry was subjected to angular distortions of up to 1 in 125—values that are close to the tolerable limit. These movements ceased only when the façades were tied into the new structure. The retaining wall and temporary works support system for the new basement proved extremely stiff and watertight. Lateral wall movements were at most 1 mm and were significantly less than those predicted before the works. Back-analysis of the performance of the retaining system suggests that the stiffness of the Dublin glacial deposits was underestimated. Level surveys showed little ground settlement, but only a relatively poor accuracy of ±3 mm was achieved. Only minor variations in groundwater level were recorded. Some minor effects, in the form of opening of cracks, were recorded on two sensitive adjacent buildings. Post-construction repair works easily overcame these.