fbpx | LEARNZ


Building a Safe Tunnel

A lot of work must be done to design a safe tunnel, prepare the site, and move underground pipes.

Digging deep into Buckle Street

  • The tunnel is not being bored through rock
  • The tunnel is a concrete box in a trench sometimes called a “cut and cover” project.

A 300 metre long trench has been dug into Buckle Street.

  • The trench is 18 metres wide
  • The trench is 12m deep at the sides for drainage and 10m deep through the middle
  • It will take 4,200 truck and trailer loads to take the soil away (38,000 cubic metres)
  • The soil is taken to a landfill where it can be used in other projects.

Underground pipes

Many pipes carrying services to homes and businesses are buried in the ground beneath Buckle Street.

These pipes carry;

  • gas
  • storm water
  • sewage
  • telecommunications
  • electricity

These services have to be moved out of the way so the trench can be dug for the new tunnel and road;

  • Using a digger might break the pipes
  • To avoid damaging the pipes, water is sprayed onto the soil around the pipes
  • The slushy water and soil is sucked up by a giant vacuum cleaner
  • The exposed pipes can then be safely worked on.

Underneath Buckle Street is a 100 year-old sewer pipe;

  • The sewer is made of bricks and is nearly a metre high
  • It will not be moved
  • It comes close to the new road at one point and extra care is being taken to protect it.

Making a Safe Tunnel

The tunnel and the road for the National War Memorial Park Underpass have been designed with people’s safety in mind.

  • Earthquakes in the past have lifted up the land in Wellington
  • The engineers are designing the tunnel to make it safe from earthquakes
  • The tunnel will be anchored to concrete piles that will go down to the bedrock (10–30 metres)
  • At first the engineers were going to use straight piles
  • They have now decided to make piles with a bell-shape at the bottom
  • The bell-shape designed will help the tunnel withstand a 1-in-2,500 year earthquake.

The engineers are making plans in case there is an accident or car breakdown in the tunnel;

  • Closed circuit cameras will keep an eye on what is happening
  • The cameras work 24 hours a day, seven days a week
  • They alert emergency services if anything goes wrong.

Safety on the work site

A wall protects the workers and keeps the soil in place while the tunnel and road are being built

  • The retaining wall is made from steel kingposts with timber poles slotted in between
  • This wall holds the trench open for the tunnel and the road to be built
  • Another wall of interlocking steel sheet posts protects the foundations of the historic Mount Cook Police Barracks and an apartment building

Keeping safe is important on the work site.

  • There are cranes, diggers and loaders moving around where people are working
  • The Memorial Park Alliance employs a safety manager who makes sure everyone knows how to work safely around machinery.

Digging begins for the underpass construction site trench. Image: NZTA.


The tunnel is being constructed as a concrete box in a trench and is known as a ‘cut and cover’ project. It is not being burrowed through rock. Image:  NZTA.


The tunnel will be anchored to 30-metre deep concrete piles to protect it in case of a major earthquake. Image:  NZTA.

Discuss two challenges in completing Memorial Park. How were these challenges managed?