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Introduction
Singapore is going below ground because it is running out of room above it. For a city-state that must fit homes, industry, defence, water, energy and nature onto one small island, the subsurface has become a planned land resource rather than a leftover space for pipes and car parks. Rock caverns already hold fuel and ammunition, deep tunnels carry used water across the island, and the Draft Master Plan 2025 commits to expanding the strategic use of underground space further, including exploring a deep cavern at Gali Batu for storing construction aggregate.
This article explains what underground space planning means, how Singapore moved from building underground project by project to mapping and safeguarding the subsurface in three dimensions, and what that shift means for planners, developers and the construction industry. It also weighs the genuine benefits of building down against the costs and risks that come with it, because the subsurface is valuable precisely because it is finite and, once used, very hard to undo.
This article explains what underground space planning means, how Singapore moved from building underground project by project to mapping and safeguarding the subsurface in three dimensions, and what that shift means for planners, developers and the construction industry. It also weighs the genuine benefits of building down against the costs and risks that come with it, because the subsurface is valuable precisely because it is finite and, once used, very hard to undo.
What is underground space planning?
Underground space planning is the practice of deciding, in advance and in three dimensions, what should go below the surface, at what depth, and in what order. Conventional land use planning works largely in two dimensions: a plot is zoned for housing, industry or open space. Underground planning adds the vertical axis, treating the layers beneath a site as distinct resources that can be allocated, safeguarded and coordinated.
The discipline matters because the subsurface behaves differently from surface land. A building can be demolished and replaced within a few years, but a deep tunnel or cavern is effectively permanent and constrains everything built around it for generations. A poorly placed basement or pile group can block a future rail alignment; an unmapped utility line can delay a project by months.
Singapore’s Ministry of National Development has argued that a first come, first served approach to the underground leads to suboptimal outcomes, which is why the country now plans its subsurface centrally. Closely related topics include geotechnical engineering, utility coordination, land law and urban resilience, all of which shape what is technically and legally possible below ground.
The discipline matters because the subsurface behaves differently from surface land. A building can be demolished and replaced within a few years, but a deep tunnel or cavern is effectively permanent and constrains everything built around it for generations. A poorly placed basement or pile group can block a future rail alignment; an unmapped utility line can delay a project by months.
Singapore’s Ministry of National Development has argued that a first come, first served approach to the underground leads to suboptimal outcomes, which is why the country now plans its subsurface centrally. Closely related topics include geotechnical engineering, utility coordination, land law and urban resilience, all of which shape what is technically and legally possible below ground.
A brief history: Singapore’s journey below ground
Singapore’s use of the subsurface began with transport. According to the government’s SG101 resource, the first MRT and road tunnels of the 1980s marked the start, and the pace picked up with the Underground Ammunition Facility in 2008. Built in rock caverns beneath the old Mandai Quarry, it freed about 300 hectares of land that conventional above-ground depots would have needed, and the surrounding granite’s natural insulation halves the energy required for cooling.
The Jurong Rock Caverns followed. Operated by JTC, the facility sits 130 metres beneath the seabed of Banyan Basin, can hold up to 1.47 million cubic metres of liquid hydrocarbons, and saves roughly 60 hectares of surface land on Jurong Island. Meanwhile, PUB’s Deep Tunnel Sewerage System has replaced conventional pumping with gravity-fed tunnels, allowing older water reclamation plants and pumping stations to be phased out and their land released.
The Jurong Rock Caverns followed. Operated by JTC, the facility sits 130 metres beneath the seabed of Banyan Basin, can hold up to 1.47 million cubic metres of liquid hydrocarbons, and saves roughly 60 hectares of surface land on Jurong Island. Meanwhile, PUB’s Deep Tunnel Sewerage System has replaced conventional pumping with gravity-fed tunnels, allowing older water reclamation plants and pumping stations to be phased out and their land released.
| Project | Completed | Depth | Land benefit |
| Deep Tunnel Sewerage System Phase 2 | Tunnelling finished 2023; full system slated for 2026 | 35 to 55 m | Frees land at Ulu Pandan and Jurong water reclamation plants and pumping stations |
| Jurong Rock Caverns, Phase 1 | 2014 | 130 m below Banyan Basin | About 60 ha saved |
| Underground Ammunition Facility, Mandai | 2008 | Several storeys, in granite | About 300 ha freed |
| First MRT and road tunnels | 1980s | Varies | Transport moved off the surface |
From ad hoc to planned: mapping the subsurface in 3D
For decades, Singapore’s underground grew one project at a time. The turning point came with the Master Plan 2019, which for the first time included an underground space plan. The Urban Redevelopment Authority (URA) released 3D underground maps for three pilot areas: Marina Bay, Jurong Innovation District and Punggol Digital District. These maps show existing and planned underground uses and the planning requirements developers must work around, making the subsurface visible and predictable to the industry.
The statutory tool behind this is the underground Special and Detailed Control Plan (SDCP). As the Ministry of National Development explained at the ACUUS 2023 conference, SDCPs mark safeguarded and planned underground uses in key areas so that long-term needs are protected before individual developments claim the space.
Land law has adapted too. Following amendments to the State Lands Act, surface landowners own the underground space down to 30 metres below the Singapore Height Datum unless their title states otherwise, which gives the state a clear basis for planning deeper layers. For context, typical basements in Singapore extend to about 15 metres, so most private development sits comfortably within that envelope.
The statutory tool behind this is the underground Special and Detailed Control Plan (SDCP). As the Ministry of National Development explained at the ACUUS 2023 conference, SDCPs mark safeguarded and planned underground uses in key areas so that long-term needs are protected before individual developments claim the space.
Land law has adapted too. Following amendments to the State Lands Act, surface landowners own the underground space down to 30 metres below the Singapore Height Datum unless their title states otherwise, which gives the state a clear basis for planning deeper layers. For context, typical basements in Singapore extend to about 15 metres, so most private development sits comfortably within that envelope.
The three layers of Singapore’s subsurface
URA’s Master Plan 2025 material on underground space groups the subsurface into three broad types of space, each with its own uses and engineering demands.
Thinking in layers is useful for planners because each layer has a different lifespan, cost profile and degree of flexibility. Basements are closely tied to individual buildings, linear networks serve whole districts, and caverns are national assets. Conflicts usually arise where these layers meet, for example where a new basement must be designed around an existing tunnel’s protection zone.
- Basement spaces. Shallower basements hold pedestrian links, retail, car parks and utility plant. Deeper basements can accommodate MRT stations and even water reclamation plants. URA has signalled it wants to widen the range of basement uses by tackling technical barriers such as fire safety.
- Linear infrastructure. Rail, roads, water, sewage and electricity lines run underground to reduce their impact on the surface. Common Services Tunnels and Utility Specific Ducts bundle several utilities together, saving space and leaving spare capacity for future lines.
- Excavated in deep, competent rock, caverns create large enclosed volumes suited to storage. The Mandai Underground Ammunition Facility and Jurong Rock Caverns are the established examples.
Thinking in layers is useful for planners because each layer has a different lifespan, cost profile and degree of flexibility. Basements are closely tied to individual buildings, linear networks serve whole districts, and caverns are national assets. Conflicts usually arise where these layers meet, for example where a new basement must be designed around an existing tunnel’s protection zone.
Pros and cons of building underground
Going below ground is not automatically the right answer. It makes most sense for uses that do not need daylight or a street frontage, that benefit from enclosure, or that impose safety buffers on their neighbours when built on the surface. The trade-offs are summarised below.
| Factor | Benefit | Cost or risk |
| Land | Frees surface land for homes, parks and community uses (about 300 ha at Mandai alone) | The subsurface is finite and, once occupied, very hard to reclaim |
| Safety and security | Rock enclosure protects stored fuel and munitions and shrinks surface safety buffers | Fire safety, evacuation and ventilation are harder to design for occupied spaces |
| Energy | Stable ground temperatures cut cooling needs, as at the Mandai facility | Continuous mechanical ventilation and pumping add operating loads |
| Construction | Disruption above ground can be limited with tunnel boring and deep excavation | Higher capital cost, longer programmes and greater ground risk |
| Geology | Competent granite suits large caverns | Variable formations, such as the folded and faulted rocks of the Jurong formation, demand careful investigation |
| Flexibility | Bundled utility tunnels leave spare capacity for future lines | Poorly coordinated works can sterilise space needed later |
The pattern is clear: the benefits are long term and city-wide, while the costs are front-loaded and borne at project level. That imbalance is exactly why central planning and safeguarding matter.
What going underground means for the built environment
The shift to planned underground space changes how projects are conceived from day one. A development in Marina Bay or Punggol Digital District can no longer treat its basement as a private matter. Designers must check the 3D underground plan for safeguarded corridors, planned pedestrian links and utility tunnels, then shape piles, retaining walls and basement levels around them. Early coordination now saves the costly redesigns that once surfaced only at the authority submission stage.
For contractors and other builders in Singapore, three practical consequences stand out:
For the wider public, the payoff is a better surface. Every substation, reservoir or storage facility moved underground, such as the 230 kV substation planned beside Labrador Park MRT Station, is space returned for housing, greenery and community life.
For contractors and other builders in Singapore, three practical consequences stand out:
- Ground investigation carries more weight. Deeper basements and work near tunnels require detailed site investigation and ongoing instrumentation, so the soil and rock profile is understood before excavation rather than discovered during it.
- Protection of existing infrastructure becomes central. Excavating close to MRT lines, deep sewers or Common Services Tunnels means designing earth retaining systems and monitoring regimes that keep ground movement within strict limits.
- Integration replaces isolation. Basements increasingly connect to neighbouring buildings, stations and underground walkways, so structural, M&E and architectural packages must be coordinated across site boundaries.
For the wider public, the payoff is a better surface. Every substation, reservoir or storage facility moved underground, such as the 230 kV substation planned beside Labrador Park MRT Station, is space returned for housing, greenery and community life.
Looking ahead: the Master Plan 2025 and beyond
The Draft Master Plan 2025 places underground space under its “Strengthening Urban Resilience” theme and sets out several directions worth watching:
The common thread is a move from building individual underground assets towards managing the subsurface as a system. That will reward projects designed with future connections in mind, and penalise those that treat the ground beneath them as theirs alone.
- New caverns. URA is exploring a cavern at Gali Batu for storing construction aggregate, a bulky but essential material that currently occupies surface land.
- Underground energy storage. Feasibility studies are assessing whether Battery Energy Storage Systems can operate safely underground to support renewable energy.
- Co-location and adaptability. Building on facilities such as the Bidadari Underground Service Reservoir and the Stamford Detention Tank, URA is asking whether larger water and energy infrastructure could move underground, and whether caverns could be designed to expand and host multiple uses over time.
- Better mapping. Geological mapping, 3D models of as-built structures and piles, and ground-penetrating radar for buried cables and pipes all reduce excavation risk and road closures.
The common thread is a move from building individual underground assets towards managing the subsurface as a system. That will reward projects designed with future connections in mind, and penalise those that treat the ground beneath them as theirs alone.
Conclusion
Singapore’s underground has evolved from a collection of tunnels and basements into a planned layer of the city. Landmark projects such as the Underground Ammunition Facility, Jurong Rock Caverns and the Deep Tunnel Sewerage System have shown that moving infrastructure below ground can return hundreds of hectares to the surface. The 3D underground plans, SDCPs and the Master Plan 2025 now ensure that future use of the subsurface is safeguarded, coordinated and visible to everyone who builds on it.
For planners, the lesson is that the ground beneath a city deserves the same foresight as the land on top of it. For the construction industry, it means deeper investigation, tighter protection of existing assets and closer collaboration across disciplines. Done well, going below ground is not about hiding infrastructure away; it is about giving people more of the surface they actually live on.
For planners, the lesson is that the ground beneath a city deserves the same foresight as the land on top of it. For the construction industry, it means deeper investigation, tighter protection of existing assets and closer collaboration across disciplines. Done well, going below ground is not about hiding infrastructure away; it is about giving people more of the surface they actually live on.
References
- Urban Redevelopment Authority, “A Singapore that is liveable, inclusive and endearing for generations: URA unveils Draft Master Plan 2025”: https://ura.gov.sg/Corporate/Media-Room/Media-Releases/pr25-32
- Urban Redevelopment Authority, “An Underground of Possibilities”, Master Plan 2025: https://www.ura.gov.sg/land-plannin...n-resilience/an-underground-of-possibilities/
- Ministry of National Development, speech at the opening of ACUUS 2023: https://www.mnd.gov.sg/newsroom/spe...ranee-rajah-at-opening-ceremony-of-acuus-2023
- JTC Corporation, “Jurong Rock Caverns”: https://jtc.gov.sg/find-space/jurong-rock-caverns
- SG101, “Singapore’s first underground ammunition storage facility”: https://www.sg101.gov.sg/resources/archives/singaporesfirst-underground-ammo-storage-facility/
- Ministry of Sustainability and the Environment, “Completion of the Deep Tunnel Sewerage System Phase 2 Tunnelling Works”: https://mse.gov.sg/latest-news/completion-of-tunnelling-works-for-dtss2
- Tunnelling Journal, “PUB completes tunnelling on DTSS Phase 2”: https://tunnellingjournal.com/pub-completes-tunnelling-dtss-phase-2/
- EdgeProp Singapore, “URA strives for a greener, more resilient, and more inclusive Singapore”: https://edgeprop.sg/property-news/ura-strives-greener-more-resilient-and-more-inclusive-singapore
- OpenGov Asia, “Singapore to unveil pilot areas of underground masterplan next year”: https://opengovasia.com/?p=6247
- Amberg Engineering, “Jurong Rock Cavern”: https://ambergengineering.com/references/projects/jurong-rock-cavern