Hydromills are specialist construction equipment that help dig narrow but deep trenches and are being used to dig the holes that will form the walls of the Lower Plenty Road and Manningham Road interchanges. You can find out more about this tunnelling method on our cut and cover page.

Once a claw like digger removes the top layers of soil, a hydromill is used to get the hole to the right depth.

The machines have 2 cutter heads on the bottom for digging out the dirt and rock. They are also fixed with pipes that pump a clay and water mixture into the hole during the dig that stabilises the soil while we excavate.

The hole is then filled with concrete to form the diaphragm walls (D-walls).