Span crack in the skytrain for the North West Rail. The Italian consortium building the viaduct has already been forced to tear down or partially replace three precast concrete spans damaged by cracking. But, in the worst case, another span buckled upwards by about 1.5 metres late last month, raising concerns about the design and the stresses that cables running through the spans have been placed under. Contractors have covered the buckled span and stationed security guards next to it in an attempt to prevent people from taking photographs. Sources say the cracks and buckling raise concerns about the structural integrity of the viaduct, and the willingness of MTR, the Hong Kong company that will eventually operate the metro line, to accept it from the Italian contractors Salini Impregilo.

A security guard attempts to stop photographs of the buckled span on the Skytrain viaduct in Sydney's north-west. Credit:Janie Barrett "There are clearly issues that are going to delay the project. It has got serious issues," one source said. "Each span is slightly different. [The unknown is whether] it could impact multiple spans or only a few." So far, 94 of the Skytrain's 121 spans have been erected. The so-called "mini Anzac Bridge" over Windsor Road is still far from complete. Credit:Janie Barrett Another source said: "There were so many red flags at so many levels. The Italians are responsible for managing their designer but the buck stops with [Transport for NSW]."

However, Transport for NSW said "construction resequencing is common" on major infrastructure projects as programs were adjusted to take into account construction activity and maintain the overall delivery program. The giant maintenance facility that will house the new metro trains at Rouse Hill. Credit:Janie Barrett "Safety is the number-one priority on Sydney Metro. We're making final preparations for the first section of the Skytrain to be handed over to the Sydney Metro Northwest operator," it said in a statement. The transport authority said Sydney Metro, the organisation charged with overseeing the rail project, was also "working closely with Roads and Maritime Services to "achieve a timely construction process". "Roads and Maritime Services' approval process takes place as required by the program of work and is obtained progressively," it said.

"Skytrain construction is being closely monitored by both its builder Salini Impregilo, as well as an independent certifier." The spans between concrete piers have an average length of 40 metres and are held in place by steel cords that run though the segments. Sources say the proof engineer for the viaduct had refused more than a year ago to sign off on the design because it was concerned stresses within the spans were too great. The sources also blamed the cracking of the spans on quality and construction issues such as the use of poor concrete. Australian engineering standards for a viaduct and cable bridge of the complexities of the Skytrain project are less stringent than in the US or Europe, where there are limits on how much stress can be placed.

However, Transport for NSW said the proof engineer had already certified the majority of the Skytrain design over the past two years. "The remaining proof-engineered designs will be certified in line with the construction requirements at the appropriate time," it said. Salini Impregilo hired as the lead designer for the viaduct and cable bridge the Melbourne firm SMEC, which was recently bought by a Singaporean company for $S400 million ($376 million). The curved cable bridge is the most challenging part of the Skytrain project, and is crucial because it will link to a massive maintenance and rail yard on the western side of Windsor Road where the driverless metro trains will be housed at Rouse Hill. Fairfax Media revealed last year that the cost of the elevated Skytrain had blown out by $50 million to about $390 million.

Loading The Baird government wants to open the metro line between Rouse Hill and Chatswood in 2019, the same year as the next state election. It will be the first stage of a $20 billion-plus rail line that will continue onto Chatswood, under Sydney Harbour to the CBD and onto Sydenham and Bankstown.