WORK crews will have to drill an extra 20 metres down to anchor the Southern Feeder Road rail bridge following further geotechnical studies.
Initial investigations said Orange City Council contractors would have to pile, or drill, three metres into the ground to build the bridge foundations, which will consist of a series of large columns on either side of the railway line.
Completion was initially expected in late November, but a recent report to councillors said the drilling depth had to be 23 metres due to insufficient strength in the rock and there would be increased costs and time involved.
The bridge will ultimately span 23 metres - the entire second stage will be 720 metres in length, joining the Forest Road intersection to Elsham Avenue via a realigned route.
Council spokesman Allan Reeder said the initial depth below the ground of the columns was designed based on industry standard geotechnical investigations of the site.
"Unfortunately, while those geotechnical results showed rock below the surface, further drilling during construction showed the depth of rock was variable across the pile set and was only a very thin layer of rock on one side," he said.
"Drilling to a greater depth will achieve the required strength in that location."
The project was costed at $18.4 million, but Mr Reeder said the council and contractor Haslin Constructions were working collaboratively to deal with the expected cost and timetable for the extra piling.
The project is expected to be completed in the new year.
Design work is almost complete for the Elsham Avenue to Mitchell Highway stretch, which is fully funded through council funds and government grants.
The section from Anson Street to Pinnacle Road is partially funded.
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