The huge dump bed which slipped about 7am today is blocking both lanes of the Peak Downs Highway at Epsom.
The mining equipment is still on the road and will require a crane to remove it.
At least four police crews remain on the scene and are diverting traffic.
A police spokesman told 9news.com.au traffic was backed up by 15 kilometres earlier.
The incident happened about 7am.
One commenter on Facebook said it was not an easy task.
“I’ve loaded these onto trucks at work before. I know what they need to put it back on … Good luck with that depending where they are,” they wrote.
Other commenters said they weren’t surprised given the state of the roads in the area.
“The roads are so bad up there and you see heaps of wrecked caravans on the sides of the roads … it’s not always driver error,” one person wrote.