Jurassic problem being fixed
THE contractor building the massive Toowoomba Second Range Crossing is halfway through remediating an embankment that has pushed back the project by more than six months.
Nexus Infrastructure has revealed it is close to removing Embankment 24 and clearing a layer of sediment formation up to 200 million-years-old, which was causing foundation movement.
The slip surface, along the corridor at Ballard east of the 800m viaduct, was discovered in February this year.
Nexus Infrastructure CEO John Hagan said the huge operation involved the removal of more than three million cubic metres of earthworks.
“Fill used to create the embankment has been moved to temporary storage areas,” he said.
“Work is well advanced in removing the layer of problem material between the ground surface and the slip surface.
“Once this process is complete, we can undertake the required foundation treatment and rebuild the embankment.
“The additional work will delay project completion until mid-2019, however, work elsewhere on the TSRC is progressing towards finishing this year.”
Earthworks are more than 95 per cent complete and bridge programs about 90 per cent finished on the $1.6 billion project.
The geological feature, formed after basalt magma flow met with an alluvial flat about 17-20 million years ago, was described as “unprecedented” by Toowoomba geologist Dr Edwin Willey when it was discovered.
Dr Willey said the flow, encased in a thick, bubbly skin, made no contact with the ground as it rode on a cushion of steam arising from the soil.
While under normal circumstances, the lava’s base would flatten and stretch against the ground, the steam prevented that happening and the bubbles were preserved, frozen in the solid base.
“It is a complex geometry of weak and strong rocks; a slope stability conundrum,” Dr Willey said.
“Such a feature has not yet been described in the geological literature.”