During the past 18 months, a series of secret tunnels have been built underneath Bangkok’s Suvarnabhumi International Airport. The presence of these structures is no surprise to airport officials, the large construction teams building them or the huge security team keeping them safe.

But a majority of the more than 60 million people who flew in and out of the airport last year likely had no idea the tunnels existed making them a secret to the public for the time being.

That will change during the next 12 months. Eventually, airport passengers will get the see the tunnels firsthand as part of an Automated People Mover (APM) system. This tram will connect the Suvarnabhumi Airport main terminal to the midfield expansion concourse also being constructed.

The expansion will increase the airport’s capacity by an estimated 15 million people annually. Work on the project began in late 2017, starting with the taxiway before moving onto the tunnels and a new concourse. More than 1.4 kilometres of tunnels will be built as part of the project including those used for the APM and service tunnels.

Suvarnabhumi Airport
A look down the tunnel which will hold the Automated People Mover (APM) system under Suvarnabhumi Airport

Thousands of passengers will be transported on the tram daily, but it’s unlikely they will pay much thought to just how the massive tunnel system came to fruition. No one really spends time to think about what goes on behind the scenes of a project like this, especially when they come to Thailand. However, the technology used in the construction of these tunnels is impressive in its own right.

How do you build secret tunnels under a busy airport?

Standing in the Suvarnabhumi Airport secret tunnels as they sit now feels a bit surreal. It is like something straight out of a movie or television show. The massive concrete walls stretch as far as the eye can see, a row of fluorescent lightening making it visible. The bulk of the current work is happening on the structures that will connect the tram to the new concourse extension.

Meanwhile, there are no signs of planes as they pass above the ground further down the tunnel. The only thing you do notice are the towering concrete panels that line the walls of the structure. As you might expect, these aren’t your ordinary walls.

They have been constructed with INSEE SUPERBLOCK, pre-fabricated concrete panels that have been designed to provide the strength and durability a project of this magnitude requires. Used in place of traditional brick and mortar, these panels are vital in the building of the Suvarnabhumi Airport secret tunnels that will soon be home to the people mover as well as a service route.

An estimated 50,000 square metres of pre-fabricated panels have been used in the building of the tunnel. It’s hard to even quantify that size, even as you look down the dimly-lit corridor with walls that seemingly never ends.

However, we’re getting ahead of ourselves. As recently as 2017, this space was nothing but dirt. Given the unique route of the tunnels, which go underneath taxiways at the airport, a few different tunnel creation methods were used to remove the earth and reinforce the structure. This was done to limit disruptions and maintain safety.

50,000 square metres of pre-fabricated panels have been used in the construction of the tunnels
50,000 square metres of pre-fabricated concrete panels have been used in the construction of the tunnels

The use of pre-fabricated materials along with traditional concrete solutions allowed builders to get the tunnel up quickly. For example, 1,000 square metres of walls inside the Suvarnabhumi Airport tunnels could be installed in roughly one week.

Perhaps the most important thing about a secret tunnel is that it needs to remain out of sight and out of mind. If the public finds out a tunnel is being built underneath the planes, it might cause people to be nervous. That’s the last thing you want to happen at the airport and means time is of the essence.

By using pre-fabricated materials, the Suvarnabhumi Airport secret tunnels went noticed by the millions of people who flew in and out of the facility. Pilots and even some staff didn’t even know about the work that was taking place underground.

It may sound crazy, but before pre-fabricated concrete panels, builders would use bricks and mortar to support underground tunnels. As you might imagine, this took a really long amount of time. For starters, loading and unloading bricks is an arduous task, but that’s only one consideration.

It’s estimated that four people building a tunnel wall with pre-fabricated panels could cover up to 24 square meters in a single day. That number shrinks to 10 square metres when the same four workers build with traditional bricks and mortar.

In other words, five day’s work can be cut into two when using pre-fabricated panels. Project contractors estimate the tunnel could have been built in less than two months if they had opted to focus all of their time and effort on the project. Ultimately this was not feasible considering they also need to work on the APM station, basement and ground levels of the concourse extension.

Suvarnabhumi Airport secret tunnels will soon be revealed

During Chinese New Year festivities, some 200,000 passengers went through Suvarnabhumi International Airport on a daily basis. And yet, underneath the airport, work continued on the Suvarnabhumi Airport secret tunnels that will allow even more people to fly in and out of the airport.

Suvarnabhumi Airport concourse extension
Work continues on the Suvarnabhumi Airport concourse extension

It’s still a dusty work site, however, the Suvarnabhumi Airport secret tunnels won’t be unknown for much longer. No set date for the opening of the APM and concourse extension has been announced as of yet, it is expected to be operational sometime in 2020.

The tram system still needs to be installed and a great deal of testing must be done, but it’s safe to say everyone will be quite happy when it does open to the public.

The parts of the tunnels people will see when using the tram are going to look quite different than what’s now visible. A thin layer of plaster will be placed over them and then a decorative coating is set to be added over that in the areas where the tram connects to the airport terminals.

It will certainly look nice and match the final design of the airport. But, behind this decorative layer will sit 50,000 square meters of pre-fabricated concrete panels that have made the tunnels possible. Without them, the project would have taken significantly more time, money and manpower.

So, if you ever fly out of Bangkok once the Suvarnabhumi Airport concourse extension opens and use the tram, enjoy the ride. There was a time when this short journey was nothing more than a secret hole in the ground.