The structural integrity of the Auckland Harbour Bridge came into question months before a truck crash damaged a span that caused traffic chaos, a Weekend Herald investigation has found.
A freak 127km/h gust of wind that overturned the truck in September last year highlighted the vulnerability of the bridge, which carries 170,000 vehicles a day, 30,000 bus commuters and critical water and power connections.
Previously confidential reports, obtained by the Weekend Herald, show the New Zealand Transport Agency, Waka Kotahi, was aware of potentially major problems with one of the bridge's pier foundations not long before the truck crash.
The reports show Government plans for a shared walking and cycling path on the Auckland Harbour Bridge were scrapped after "exceptionally weak" ground and a potential faultline were found near pier 2.
Rock samples taken from the substructure foundations taken this year to test the wind and seismic load of the shared path found the rock was not as strong as expected for the design of the shared path.
Transport Minister Michael Wood said he was made aware about the "exceptionally weak" ground and potential faultline near pier 2, which is why he announced in June this year the Government would not be proceeding with the shared path attached to the harbour bridge.
At the time, he said geotechnical investigations and testing meant the shared path on the bridge was not possible without considerable modifications, but did not mention the weak ground and a possible faultline.
Wood announced a new separated walking and cycling bridge costing $685 million in June, but last month Prime Minister Jacinda Ardern and Finance Minister Grant Robertson all but confirmed the unpopular cycle bridge will not proceed.
Details about issues with the piers are spelled out in confidential reports to Waka Kotahi, which the Weekend Herald has been seeking under the Official Information Act since last December.
Waka Kotahi initially refused to release 14 reports into the risks of building the shared path, prompting the Chief Ombudsman Peter Boshier to launch an investigation in July. Last week, the transport agency released 11 reports and a brief summary of the other three.
"Geotechnical investigation of one or two boreholes to each pier found a potential fault line adjacent to pier 2 and the ground adjacent to pier 2 found to be exceptionally weak," said a November 2020 report into the feasibility of attaching the shared path to the existing bridge.
Two weeks earlier, a report by the engineering firm Beca said: The outcome of the geotechnical investigations was that rock strength was found to be lower than anticipated at the concept design stage, for some piers. Differing ground conditions were discovered across the critical foundation at Pier 2 and a potential fault was identified on the western side of the [bridge]."
Pier 2 is one of eight on the bridge and is south of the main navigation channel.
Waka Kotahi said further dive inspections were carried out on September 2 last year by New Zealand Diving and Salvage under the supervision of Beca.
The inspections found the piers to be in "generally fair conditions with no sign of major defects" and good sound concrete was found in all areas investigated.
The transport agency said in relation to the weaker than expected rock at a borehole near pier 2, extra strengthening would only be needed for the shared path, not for the existing bridge.
Waka Kotahi chief executive Nicole Rosie did not respond to a request to release the Specimen Design Report into the September investigations. A Waka Kotahi spokeswoman said the request would be processed as an Official Information Act request.
In February this year, Waka Kotahi general transport service manager Brett Gliddon told a parliamentary select committee the ageing harbour bridge cannot take any more strengthening and traffic will have to be restricted to maintain its "structural integrity".
"We believe we've strengthened it as much as we possibly can and we can't add more steel into it."
The bridge was last upgraded in 2010, when about 900 tonnes of steel was bolted onto the clip-ons to extend the bridge's life by between 20 and 40 years.