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Heavy rain damaged track before train derailed: ATSB

A freight train derailment cutting off an interstate rail corridor was the symptom of heavy rain causing an embankment supporting the track to collapse, a preliminary report says.

16 carriages from the 1.7 kilometre-long train went off the tracks at Inverleigh, near Geelong, on the morning of November 14 last year.

No one was injured in the derailment, although the Melbourne to Adelaide rail corridor was blocked for some days.

A preliminary report from the Australian Transport Safety Bureau, released on Friday, stated the freight train was travelling about 80km/h over a culvert when it derailed.

An embankment supporting the track at that culvert had collapsed after significant rain lashed the area for 12 hours before the incident, the report said.

Investigators have examined drainage in the waterway catchment area and started hydrology studies, chief investigator Mark Smallwood said.

There will be further reviews of the weather warnings in the area, the effect of rainfall on soil moisture and the culvert design.

The maintenance of track infrastructure and train operation will also be assessed.

A final report will be released at the end of the bureau's investigation.

"However, should a critical safety issue be identified during the course of the investigation, relevant parties will be notified immediately, so appropriate and timely safety action can be taken," Mr Smallwood said on Friday.