The Port Hedland Under Harbour tunnel is a 4.3m internal diameter EPB TBM driven tunnel excavated in sedimentary sandstone and conglomerate formations underlying the alluvial deposits beneath Port Hedland Harbour. The tunnel was lined with 250mm thick, gasketed, precast concrete segments. These segments are corroding due to infiltrating saline water. As a remedial measure it was proposed to reline the tunnel with a prefabricated, internal circumferential steel liner, site welded to form a continuous structure, with the annulus backgrouted against the concrete segments to allow load transfer. These thin steel tunnel liners subject to external hydrostatic pressures are highly prone to failure from buckling.

Dr Bedi was employed to undertake detailed geotechnical analysis, review of the existing tunnel condition and preparation of design, construction sequencing and staging arrangement of an internally jacked steel liner. The steel liner was required to be designed to withstand the full structural load from the overlying harbour and rock due to future deterioration of the concrete segments. Advanced geotechnical Finite Analysis and Non-linear Buckling Analysis of the steel liner was required to ensure adequacy not only from ground and hydrostatic loading but also due to forces incurred from flotation of the tunnel during annular grouting during the construction stage. This project was used as the subject of a upcoming publication “Finite Element modelling of load shed from deteriorating segmental lining and non-linear buckling solutions of confined tunnel liners”.