Small wall deflections of less than 10mm were mobilised during the construction of a 56.6m diameter 28m deep circular TBM launch and reception shaft for the Dublin Port Tunnel Project. A series of FE analyses were performed to predict wall behaviour during deep excavation. Initial shaft behaviour involved cantilever deflection of individual diaphragm wall panels as initial inter-panel gaps closed and a small hoop stiffness was mobilised by the cylindrical shaft structure. Subsequent excavation phases involved bulging of the mid and lower portions of the shaft as a higher hoop stiffness is mobilised by the structure and small rotations occur about the mid level ring beam. Small creep and consolidation related movements, no more than about 3mm, occurred during pause periods.
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