Building response to adjacent deep basement construction

Field observations of the response of a building adjacent to a 23-m-deep basement excavation for a development adjacent to Harrods department store in London, are presented and discussed. This paper focuses on No. 3 Hans Crescent located within the most critical zone, on a re-entrant corner, of the excavation. Top-down construction and underpinning techniques were implemented to minimise ground movements and building damage. Vertical and horizontal displacements were monitored using precise levelling and total station surveys, allowing building responses to be synthesised and related to construction activities. Primary observed and deduced trends are that the effects of underpinning and diaphragm walling were local, whereas piling and excavation had a global impact, and that settlement was primarily caused by diaphragm walling and piling, whereas piling and excavation caused the most horizontal displacement. The zone of influence of horizontal displacements extended farther than that for vertical displacements, which became negligible at a distance of about twice the excavation depth. The No. 3 Hans Crescent property experienced hogging for most construction stages, and sagging developed towards the end of excavation, with in-plane distortions of the building walls and out-of-plane tilting. Observations from monitoring results and post-construction condition surveys indicate that the damage category was negligible, corroborating pre-construction predictions.