Building a Safe Tunnel

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.