Inside a former granite quarry in Mandai, Singapore has built one of its most ambitious spatial engineering solutions to address the country’s most fundamental constraint: a severe shortage of land.
An ammunition storage facility constructed deep inside granite caverns has freed up around 300 hectares of surface land that previously had to remain unused for safety reasons, an area equivalent to roughly half the size of Pasir Ris New Town or 400 football fields.
When an Ammunition Depot Takes Up Too Much Land
The story began with the Seletar East Ammunition Depot, a facility inherited from the British colonial era that was eventually earmarked by Singapore’s Urban Redevelopment Authority (URA) for redevelopment. The Ministry of Defence (MINDEF) faced a choice: rebuild a conventional ammunition depot on a new site, or find a fundamentally different approach.
The problem was that a conventional ammunition depot requires far more land than the buildings themselves occupy. Safety regulations require the surrounding area to be “sterilised”, meaning it must be kept free from other uses to maintain a safe distance between the ammunition storage areas and the public in the event of an explosion.
The greater the ammunition capacity, the larger the area that must be kept clear. For Singapore, that land could not simply be put to other uses, making it an increasingly costly constraint.
In his speech at the facility’s opening on March 7, 2008, then-Minister for Defence Teo Chee Hean said rebuilding a conventional depot was not considered optimal from a land-use perspective.
Moving the Depot Into the Granite
The answer came from underground. MINDEF engineers proposed building the ammunition depot inside the disused Mandai Quarry, making use of the caverns formed within the granite rock.
Instead of constructing large storage buildings on the surface, the project would move the facility deep below ground.
The result exceeded expectations. According to Teo, the Underground Ammunition Facility (UAF) required more than 90 percent less sterilised land than a conventional depot with equivalent capacity. The site’s hard granite formations became part of the facility’s protection system, helping contain the risks of an explosion deep below the surface.
Above ground, the forest and surrounding land could remain intact. The area is now also used as a training ground by the Singapore Armed Forces (SAF).
In effect, the land that once had to be kept empty did not disappear from Singapore’s limited land supply. Its use was simply moved underground.
Building What Had Never Been Built Before
But excavating a vast underground space was only the beginning. The UAF was described as the world’s first large-scale underground, container-based ammunition storage facility built in such a densely urbanised environment. Because there was no established industry standard for a project of this kind, the engineering team had to develop many of its solutions from scratch.
At the time, scientific data on how structures respond to explosions was largely drawn from studies of earthquakes and mining blasts. The team therefore conducted extensive simulations and scaled shock-wave tests using mixed soil and rock media.
The research involved Nanyang Technological University, the National University of Singapore, Sandia National Laboratories in the United States, Sweden’s Defence Research Agency (FOI), and the Norwegian Defence Estates Agency. The findings were presented at international conferences and published in scientific journals.
From planning to commissioning, the entire project took more than a decade.
From Storage Depot to Ammunition Logistics System
Inside the caverns, the UAF is more than a giant warehouse. It was designed as an integrated ammunition logistics system.
Ammunition is stored in containers that can be stacked to maximise space while speeding up retrieval. Loads for specific missions can also be prepared inside the facility, then loaded directly onto commercial tractor-trailer trucks for transport to the field.
The entire process, from storage and retrieval to scheduling, is managed through the Ammunition Depot Management System. This allows the UAF to operate with around 20 percent fewer personnel than a conventional facility. The natural insulation provided by the granite caverns also reduces the energy required for cooling by up to 50 percent.
Once the UAF was completed and the Seletar East Ammunition Depot was decommissioned, around 300 hectares of land that had previously been required for sterilisation were returned by MINDEF to the URA for further development.
The approach later continued with other underground projects, including the Jurong Rock Caverns, which began operations in 2014. Five caverns extending nine storeys underground were built to store petroleum products, freeing up an additional 60 hectares of surface land.
