Video Summary
Troll A is a Norwegian offshore gas platform in the North Sea, 70 km off Norway’s west coast; at 472 m tall and 1.2 million tons, it’s the tallest and heaviest object ever moved.
Built between 1991 and 1996, the platform was constructed on land then towed 200 km to its site in a seven-day journey.
Its four concrete legs (each 365 m tall, 2 m thick) were cast by continuous slip-form pouring and reinforced with steel grids to add flexibility against wave loading.
Engineers submerged the legs and filled them with water to align and attach the deck — raising the legs by pumping out water for the final mating.
Vacuum anchors secure the platform on the seabed; the legs and bracing are designed to withstand up to 30 m waves and an estimated 180 million large waves over decades of service.
Building on land allowed safer, controlled construction of the enormous deck and legs; once complete the deck and legs were floated and towed to the site because in‑situ construction of such massive elements in the hostile North Sea would have been far riskier.
Slip forming is a continuous concrete-pouring method that creates seamless, watertight towers. It was used to build each 365 m leg efficiently and robustly under constant pouring to meet strict strength and durability needs.
Engineers lowered the legs into the water and filled them with ballast to submerge them, then positioned the deck just above the legs and gradually pumped out water to raise and lock the legs into place—avoiding the higher risk of hoisting the deck.
Vacuum anchors create powerful suction on the seabed to hold the platform in place, supplemented by the conical leg geometry and cross‑bracing that distribute wave forces.
To compensate for falling reservoir pressure, two compressors were added in 2014 and a module with living quarters and control room was installed in 2010 to support operations.
"Seventy kilometers off the west coast of Norway lies a beast of gargantuan size, a monster so large it remains the tallest and heaviest object ever moved across the surface of the Earth."
The Troll A platform is a massive offshore structure located in the Troll gas fields, approximately 70 kilometers from Norway's western coast.
It is recognized as the tallest and heaviest object ever moved, with a height of 472 meters, surpassing the Petronas Towers in Kuala Lumpur.
Weighing an astonishing 1.2 million tons, this platform is one and a half times heavier than the Golden Gate Bridge.
Although it is no longer the largest offshore platform due to the newer Burkett platform in Russia, its size is still unimaginably colossal.
"Construction of the Troll A platform began in 1991 and was finished in 1996."
The construction process for the Troll A platform was highly complex and divided into two main parts: the main gas platform and the four concrete legs.
The platform was built on land and then towed out to sea, employing a construction method known as slip forming.
The slip forming technique involves continuous pouring of concrete to create a seamless and watertight structure, originally developed for grain silos in the late 19th century.
With an average pouring time of 20 minutes for five centimeters of concrete, it took around 100 days to complete a single tower.
"The support towers needed to be incredibly strong but also flexible enough to bend slightly under pressure."
Given the harsh environment of the North Sea, the Troll A platform's legs were designed to withstand waves reaching up to 30 meters high.
Engineers anticipated that the platform would encounter around 180 million large waves over its operational lifetime, necessitating robust support structures.
The legs were constructed using flexible concrete, integrating steel grids to enhance flexibility while maintaining strength.
Each leg measures 365 meters tall and two meters thick, with a conical shape that further reinforces the structure against wave impact.
"The most perilous part of the entire process came when the platform and the legs needed to be joined."
A critical point in the construction was the attachment of the platform to its legs; engineers chose to lower the legs into the water rather than raise the platform.
Past experiences in Norway informed this decision, as previous mishaps illustrated the risks involved in such operations.
The legs were filled with water to aid their submersion, allowing the platform to be accurately positioned just above them before the water was pumped out, slowly raising the legs until they connected securely.
The final assembly involved precise maneuvers to ensure that the platform could clear the underwater reef before being fully submerged.
"The journey of the Troll A platform from its ford base to its final location proved to be an enormous television draw in Norway."
The Troll A platform was transported 200 kilometers from the construction site in the small village of Vats to the Troll gas fields using ten boats.
This journey took seven days, during which the platform's vast weight pressed down on the sea floor upon arrival.
To secure the structure in place, vacuum anchors were employed, creating a powerful suction that held the towering platform firmly on the seabed.
Once anchored, the platform was fully prepared for operations, with gas extraction processes commencing from a network of wells at its base.
"In 2014, two further compressors were added to the trolley because the gas pressure had dropped since operations began in 1996."
The gas operations on the Troll A platform have required upgrades over the years to maintain efficiency. Initially, in 2014, the platform saw the addition of two compressors to counteract a drop in gas pressure.
To support these new compressors, a module with living quarters and a control room was added in 2010, reflecting the platform's ongoing expansion in functionality.
"Like its two Troll cousins, the trolley uses horizontal wells which involve two separate drilling operations."
"In 2008, the gas being pumped out across these three Troll platforms was roughly 120 million cubic meters per day."
The production of gas on the Troll A platform has been substantial. In 2008, it was reported that the combined output from the three Troll platforms was about 120 million cubic meters of gas per day.
Current data on production isn't specified, but there's a regulatory cap set by the Norwegian government of 36 billion cubic meters per year, ensuring a sustainable approach to gas extraction.
"This platform cost $650 million to build, equivalent to just over $1 billion today."
The Troll A platform represents a significant financial investment, costing $650 million at the time of construction, which equates to over $1 billion in today's currency. Operated by Equinor, the platform stands as a testament to Norway's advancements in the energy sector.
Notably, the platform is not only the heaviest structure ever moved but also the tallest object if it were positioned on land, potentially ranking as the 13th tallest structure worldwide.
"Troll A's vacuum anchors hold it firmly in place amidst frigid waves battering it daily."
