Analysis of pre-vault tunnelling interaction with buildings

This paper presents data from a case history of tunnelling using the pre-vaulting method, at low cover and without compensation grouting, beneath a terrace of masonry buildings at Ramsgate, Kent. Surface and building settlements were measured and movements on existing cracks monitored throughout construction. Volume loss was low and the settlement trough quite narrow. Buildings responded flexibly with lower damage level than predicted by assessment using a deep beam analogy. Damage was concentrated in opening of existing cracks, with the only significant new cracks likely to have their origin in three-dimensional effects as the tunnel heading approached the buildings. Assessment of tunnelling effects on buildings is important to confirm the viability of new tunnelling projects and reassure building owners of the possible level of damage, while avoiding excessive conservatism. Numerical modelling shows potential for such assessment, and a procedure for modelling the ground, tunnel and building together using non-linear three-dimensional finite-element analysis has been applied to this site. It was found that, although geometry and other features of the site required simplification due to practical limitations in computing resources, model results still reflected the main features of observed response including the ‘greenfield’ trough, flexible structure response and damage severity.