Technology: Karapiro Viaduct

The Karapiro Gully viaduct under construction.

The Karapiro Gully viaduct is one serious piece of engineering. It is a bridge 200m in length with the deck 40m above the gully floor. It is part of the Cambridge section of the Waikato expressway.

  • Watch the viaduct get built on the videos page
  • Read on for the full story: The Right Bridge For a Tricky Place

The Basic Facts

The word viaduct means a bridge made up of several spans to cross a valley. Three sets of columns hold the bridge up.

The columns rest on large concrete pads on the ground, but the bridge doesn’t stop there. It is supported on piled foundations which go deep into the ground. The deepest piles go 55 metres underground.  A large crane whacked the piles into the ground with a giant hammer.

The top of the bridge is called the superstructure. This is made of large steel beams. On top of the beams is the deck, made from precast concrete panels. More concrete was poured on top of the panels and then the actual road surface was laid.

The steep banks of the Karapiro Gully and the meandering Karapiro Stream made the gully a challenging place to work. The construction team:

  • built a heavy duty access road down to the bottom of the gully
  • installed a temporary bridge to cross the stream
  • cut back slopes to create a safe working space
  • put down rock to make the ground stable enough for the heavy machinery.

More interesting facts

It took 77 days to hammer all 64 piles into the ground and fill them with reinforcing steel and concrete.

The viaduct columns are 2.6 metres diameter of solid concrete. The two columns for the central pier are the tallest at a height of 35m.

The mobile crane used to lift steel beams into place weighs 280 tonnes. For the more difficult lifts, it needed help from another 150 tonne crane.

Workers were lifted up to special working platforms where they used 23,000 bolts to hold all the steel beams in place.