Behaviour of the diaphragm walls of a cut-and -cover tunnel constructed in boulder clay at Finchley

Field instrumentation has been installed to investigate the performance of the diaphragm walls of a cut-and-cover tunnel during and after construction. The tunnel traverses the ridge of a boulder clay outlier at Finchley and was constructed as part of the A406 North Circular Trunk Road Improvement between East of Falloden Way and East of High Road. The tunnel was constructed top-down with an integral roof slab installed between the planar diaphragm walls prior to bulk excavation and the construction of a structural carriageway slab. Measurements of porewater pressures and ground movements were taken during wall installation and all stages of tunnel construction. Instrumentation was also installed in the wall panels to monitor lateral movement and bending moments developed during construction. Axial loads in the roof and carriageway prop slab were also measured. (A)