Special Underground Engineering
At the Heart of Terminal 3

It Gets Wet

During the special underwater engineering phase, the pit’s depth is increased from eight to 11 meters. This is necessary in order to build Terminal 3 so that departing travelers can conveniently do everything on one level, from check-in all the way to boarding, without having to walk up or down any stairs. Two underground levels will accommodate a large part of the highly complex equipment required to operate the new terminal.

To drive the retaining walls into the ground more easily, first the soil is loosened.

Gigantic construction machines called piling rigs lift and move the reinforced steel plates.

Each of the steel plates is 14 meters long.

A vibratory pile driver mounted on caterpillar treads uses its long gripper to pick up a retaining wall section, position it, and drive it into the ground.

Each section is inserted into the ground so it’s flush with the others that are already in place.

Only the tops of the retaining walls poke out of the ground.

Each retaining wall consists of multiple hooked-together sections.

The retaining walls are anchored in the ground to ensure that they are stable and able to withstand the pressure of the soil.

The special underground engineering work is making fast progress.

Now the individual fields of the pit are easy to see.

The excavation work starts under dry conditions.

Shaken not stirred!

In order to seal and stabilize the pit’s fields, they are surrounded by 14-meter-long steel-plate retaining walls. A total of 46,000 square meters of plates consisting of 7,100 tonnes of steel are used. The pit is about as large as six soccer fields the size of the one in Frankfurt’s Deutsche Bank Park (formerly the Waldstadion).

A sturdy foundation

As the fields are excavated deeper, they fill up with groundwater. Before it can be pumped out, however, first the bottom has to be sealed with concrete. Trained industrial drivers monitor this work. Terminal 3 requires a stable foundation. About 3,500 anchors are therefore embedded in the submerged pit bottom before 39,000 cubic meters of concrete are poured underwater. As the concrete cures, it will bind to the anchors and be prevented from rising.

Astronauts under water

Divers in construction? Most people are amazed to learn about the important role they play. When a building pit extends below the water table and temporarily floods, certified divers come into play. They wear suits that resemble those used in outer space and weigh up to 35 kilos, supplemented by a helmet weighing another 12 kilos that keeps them supplied with oxygen and lets them communicate with the site manager up above. The suits are made of neoprene lined with special thermal wool, a must considering that the water can be just a few degrees above the freezing point.

From sand across water to concrete

It takes between 30 and 50 days for the concrete to cure completely under water. Then the last phase of the special underground engineering work can begin: pumping out the groundwater and purifying it in a multistage process. It is then returned to the earth elsewhere via a specially installed infiltration system that guides it into deeper soil layers. While this is going on, it’s important to continually check the groundwater and systems to ensure seamless quality control.

Excavators continue digging until the fields reach their final depth of between eight and 11 meters.

The anchors protruding from the ground.

The pit has been divided into fields and excavated to well below the water table.

The construction site is temporarily covered with large ponds.

Trained industrial divers monitor the work in the basins.

A special processed is used to remove mud and soil from the groundwater.

The divers have visibility of no more than a meter.

The divers inspect the bottom to see if it is ready for concreting and make sure that the poured concrete forms a level surface.

The concrete enters the basin via a large crane arm. Trucks line up to ensure a steady supply.

After the water has been pumped out, empty pits remain.

The extracted groundwater is purified in a multistage process.

While some of the pits are stilled filled with water, work on the carcass of the main terminal building begins in the emptied ones.

Concrete is poured into the last water-filled pit in October 2019.