UPDATE: Ancient volcanic lava flows discovered in the Lockyer Valley have blown out the Toowoomba Second Range Crossing construction by up to seven months.
Ground movement monitoring on part of the bypass build in the Lockyer Valley discovered the effects of the lava flows and pre-Jurassic sedimentation formations that date back to between 25 million and 200 million years ago.
Nexus Infrastructure CEO John Hagan said additional excavation was needed in the small section of the project after ground movement was identified in the geological layers below an embankment at Ballard.
"Despite extensive geotechnical investigations during the detailed design phase, the ground movement was caused by an ancient slip surface which is contained entirely within the project boundary and has no impacts outside the alignment," Mr Hagan said.
"Active monitoring of the project's cuts and embankments has been ongoing since construction began, and it was this monitoring that led to the identification of the issue."
The discovery has delayed the project completion by four to seven months.
"We have been carrying out intensive investigations alongside geological experts, design specialists and the Department of Transport and Main Roads," Mr Hagan said.
"Working together, we have decided the best way forward is to carry out extensive earthworks at this location to remove the slip surface and construction he foundation of the embankment at a deeper level.
"While the project is progressing well, these additional earthworks will cause delay to the overall completion of the TSRC.
"Nexus is committed to building a quality road for the transport industry that will provide a more efficient link between Melbourne-Brisbane and Darwin-Brisbane for Australia's growing freight industry."
EARLIER: Nexus Infastructure has confirmed that the $1.6 billion Toowoomba Second Range Crossing will not be finished on time.
In a statement provided to The Chronicle, Nexus said complex geological issues were to blame.
"Nexus has informed the Queensland Government that it is expecting a delay of around four to seven months for the completion of the Toowoomba Second Range Crossing," the statement read.
"Nexus has advised that while the project is progressing well overall, the delay is due to a complex geological issue under one of the embankments in the Ballard area.
"The issue has resulted in Nexus changing the construction methodology and building the foundation of the embankment from a deeper level. As a result, extensive additional earthworks are now required in a small section of the project.
"All other scheduled activities for the project are progressing well and will continue as planned.
"Nexus will update the community as soon as the extent of the delays and construction impacts are known."
Nexus had previously stated that the project would be completed by late 2018.