Digging Deep: A Geotechnical and Structural Engineering Masterclass on Singapore’s Underground Rock Caverns

The Subterranean Imperative: Why Singapore Builds Down

he development of large-scale underground rock caverns in Singapore is not merely an engineering novelty; it is a calculated response to a fundamental national constraint and a cornerstone of its long-term strategic planning. For a city-state with a land area of approximately 716 km² and a population of over 5.6 million, the competition for surface space is intense.1 This section explores the strategic drivers that have propelled Singapore to become a global leader in subterranean development, moving from reactive problem-solving to the creation of a new, highly valuable national asset.

 

1.1 From Land Scarcity to Strategic Depth

 

Singapore’s journey into the earth began with the realization that its traditional methods of space creation were reaching their physical and economic limits. For decades, the nation relied on two primary strategies: building upwards and reclaiming land outwards. High-rise construction, while defining the city’s skyline, is constrained by aviation height restrictions necessary for civil and military air traffic in a compact nation.3 Land reclamation, which has increased Singapore’s land size by over 22% since 1965, faces escalating challenges, including the increasing cost and scarcity of sand, deeper waters for reclamation, and significant environmental and geopolitical considerations.2

Faced with these diminishing returns, Singapore’s planners began to view the subsurface not as an obstacle, but as a new frontier for development—a source of “strategic depth”.2 This strategic pivot reframed underground space as a resource to be systematically “mined” to support continued economic growth and enhance urban liveability.2 The move underground was thus elevated from a tactical choice to an “economic imperative,” essential for the nation’s sustainable future.1 This approach allows Singapore to decouple its economic ambitions from its physical land constraints, creating a new dimension for national development.

 

1.2 The Economic and Security Dimensions

 

The decision to develop underground caverns is underpinned by powerful economic and security logic. The primary economic driver is the opportunity to free up valuable, high-cost surface land for what planners term “higher value-added activities”.9 Industrial facilities, utilities, and storage depots, which are land-intensive but do not necessarily require a surface presence, can be relocated underground, releasing prime real estate for revenue-generating commercial, residential, or advanced manufacturing uses.

The Jurong Rock Caverns (JRC) project is the quintessential example of this strategy in action. Developed by JTC Corporation, the JRC was conceived to provide critical infrastructural support for Singapore’s petrochemical sector, which constitutes about a third of the country’s manufacturing output.11 By creating 1.47 million cubic metres of subterranean storage for liquid hydrocarbons, the JRC directly supports the operations of global giants like Shell, ExxonMobil, and Chevron Phillips on Jurong Island.10 This strategic infrastructure investment not only enhances the security and stability of feedstock supply for these companies but also frees up 60 hectares of surface land—enough to house up to six new petrochemical plants—thereby reinforcing Singapore’s standing as a leading global energy and chemicals hub.11 While the initial capital cost of building underground is significant—about 30% more than equivalent surface facilities on reclaimed land—the long-term economic benefit of unlocking prime industrial land justifies the investment.11

Parallel to the economic rationale is a compelling national security driver, best exemplified by the Underground Ammunition Facility (UAF). As a nation that must provide for its own defense within its city limits, Singapore faces unique challenges in storing military munitions safely.3 Conventional above-ground depots require vast safety buffer zones, or “sterilised land,” to mitigate the effects of any potential accidental explosion. By moving its ammunition storage deep into the competent granite rock mass under the Mandai Quarry, the Singapore Armed Forces (SAF) achieved a 90% reduction in this sterilised land requirement, freeing up an immense 300 hectares for other national development needs.15 The UAF not only enhances land use efficiency but also improves the security and resilience of the nation’s defense logistics.3

 

1.3 Institutionalizing the Vision: The URA Underground Master Plan

 

The success of pioneering projects like the UAF and JRC demonstrated the immense potential of subterranean development, prompting a shift from ad-hoc projects to a comprehensive, institutionalized national strategy. In 2007, the government established an inter-agency Underground Master Planning Task Force to formalize this vision.3 Today, the Urban Redevelopment Authority (URA) spearheads the development of Singapore’s Underground Master Plan, a statutory land use plan that guides subterranean development over a 10- to 15-year horizon.19

The core principle of the Master Plan is to strategically relocate infrastructure underground where it is “meaningful and feasible” to do so, thereby improving the quality of the above-ground urban environment.8 The plan prioritizes moving utilities, transport networks, storage facilities, and industrial uses into the subsurface, freeing the surface for people-centric purposes like housing, parks, community spaces, and recreation.8

A key innovation in this governance framework is the use of advanced digital tools. As part of the broader “Virtual Singapore” initiative, which aims to create a dynamic 3D digital twin of the city, the URA is rolling out 3D Underground Special Detailed and Control Plans.21 These detailed 3D maps, first piloted in areas like Marina Bay, Jurong Innovation District, and Punggol Digital District, show existing and planned underground uses, including MRT lines, utility tunnels, and pedestrian links.22 By making this information transparent to developers and planners, the URA can facilitate better-coordinated development, avoid potential conflicts between different underground uses, and ensure the efficient and holistic management of this finite subterranean resource.2 This systematic approach, backed by legislative changes that clarify state ownership of deep subterranean space, transforms the underground from a “Wild West” of development into a carefully managed national asset.7

This entire arc—from identifying a core constraint, to building capability through a strategic security project, to commercializing that capability for economic gain, and finally to institutionalizing a long-term governance framework—demonstrates a sophisticated national strategy. It is a process that has transformed a fundamental weakness into a high-value, technology-driven competitive advantage, showcasing a model of urban planning and resource management that is studied globally.

 

Section 2: Pioneering the Depths: Foundational Case Studies

 

Singapore’s journey into large-scale rock cavern development is anchored by two landmark projects: the Underground Ammunition Facility (UAF) and the Jurong Rock Caverns (JRC). While both are feats of engineering, they represent two distinct phases in the nation’s strategic evolution. The UAF served as the crucial catalyst, a state-led endeavor to build capability and prove a concept. The JRC represents the maturation of that capability, a commercially driven masterpiece that pushed engineering boundaries to support a key economic pillar.

 

2.1 The Catalyst: The Underground Ammunition Facility (UAF)

 

Completed in 2008, the UAF was Singapore’s first major foray into rock cavern construction and stands as a pivotal moment in the nation’s urban development history.15 Developed by the Singapore Armed Forces (SAF) and the Defence Science & Technology Agency (DSTA), its primary purpose was the strategic storage of military munitions.13 The project was a direct response to the immense land-use constraints imposed by conventional ammunition depots, which require extensive safety buffer zones.3

The choice of location was deliberate and strategic. The UAF was constructed deep within the competent rock of the Bukit Timah Granite formation, under the site of the old Mandai Quarry.15 This selection of a strong, stable, and well-understood geological medium was a prudent risk-mitigation measure for a first-of-its-kind national project. The granite, with a strength up to six times that of normal concrete, provided natural fortification and containment.17

The impact of the UAF was transformative. By moving ammunition storage underground, the project freed up an astonishing 300 hectares of surface land, an area equivalent to 400 football fields or half of a typical public housing town.15 Beyond land savings, the facility introduced significant operational efficiencies. The use of automation, IT systems, and innovative designs like the containerized storage system reduced manpower requirements by 20% compared to a traditional depot.15 Furthermore, the natural insulation provided by the surrounding granite caverns cut energy consumption for cooling by 50%, a significant operational and environmental benefit.15

The legacy of the UAF extends far beyond its physical footprint. It served as the crucial proof-of-concept that demonstrated the viability and immense benefits of using deep rock caverns in Singapore.5 The project was a crucible for developing local engineering expertise in a highly specialized field. The extensive research and testing conducted for the UAF, particularly on underground explosive storage safety, set new international standards that were subsequently endorsed by NATO.17 This established Singapore as a credible global player in rock engineering and directly paved the way for more ambitious projects, most notably the Jurong Rock Caverns.15

 

2.2 The Commercial Masterpiece: The Jurong Rock Caverns (JRC)

 

Officially opened in 2014, the Jurong Rock Caverns represent the commercial and technological culmination of the capabilities developed during the UAF project.13 As Southeast Asia’s first commercial underground facility for storing liquid hydrocarbons, the JRC was a massive and complex undertaking, with Phase 1 costing S$950 million.11 Its purpose was explicitly economic: to anchor and enhance Jurong Island’s status as a world-class petrochemical hub.10

The JRC project pushed engineering boundaries far beyond the UAF. The caverns are located up to 150 metres deep, crucially, beneath the seabed of Banyan Basin off Jurong Island.9 This sub-seabed location, combined with the challenging geology of the Jurong Formation, presented a significantly higher level of technical difficulty and risk compared to the UAF’s inland granite site.9 The project involved excavating five enormous caverns, each with dimensions of 27 metres in height, 20 metres in width, and 340 metres in length—as tall as a nine-storey building.13 Together with 8km of access tunnels, Phase 1 created 1.47 million cubic metres of storage capacity, freeing up 60 hectares of prime industrial land on the surface.9

The most significant design innovation of the JRC is its reliance on the principle of hydraulic containment, a concept unprecedented in Singapore’s construction history.9 Instead of being housed within expensive, impermeable concrete or steel linings, the stored oil is in direct contact with the rock mass.33 Containment is achieved by using a sophisticated “water curtain” system—a network of dedicated galleries and boreholes that actively inject water into the surrounding rock.32 This ensures that the pressure of the groundwater in the rock is always higher than the pressure of the liquid hydrocarbons stored inside the caverns. Consequently, any seepage is of groundwater flowing

into the caverns, which is then collected and pumped out, rather than product leaking out.9 This elegant solution harnesses natural hydrogeological principles to provide a safe, robust, and cost-effective containment system.

The following table provides a direct comparison of these two seminal projects, illustrating the clear progression in strategy, complexity, and innovation.

Feature	Underground Ammunition Facility (UAF)	Jurong Rock Caverns (JRC)
Purpose	Strategic military ammunition storage 15	Commercial storage of liquid hydrocarbons 13
Owner/Developer	Ministry of Defence / DSTA 15	JTC Corporation 10
Location	Under Mandai Quarry (inland) 15	Under Banyan Basin, Jurong Island (sub-seabed) 9
Geology	Bukit Timah Granite (Igneous) 17	Jurong Formation (Sedimentary) 32
Depth	Undisclosed, several storeys deep 15	Up to 150m below ground, 130m below seabed 10
Scale & Land Saved	~300 hectares (400 football fields) 15	60 hectares (84 football fields) 13
Key Innovation	Establishing large-scale cavern viability, setting new safety standards, containerized storage systems 17	Unlined hydraulic containment (water curtain), sub-seabed construction, commercial application 9
Legacy	Built national capability, catalyst for future projects 15	Reinforced Singapore’s petrochemical hub status, demonstrated commercial viability 10

 

Section 3: The Ground Truth: Navigating Singapore’s Complex Geology

 

The success of any underground construction project is fundamentally dictated by the ground conditions. In Singapore, cavern development has been concentrated in two main geological formations, each presenting a unique set of opportunities and challenges: the highly variable Jurong Formation and the strong but deeply weathered Bukit Timah Granite. A thorough understanding of their respective rock mechanics and structural geology is paramount for safe and efficient design and construction.

 

3.1 The Jurong Formation (JF): A Study in Variability (JRC Site)

 

The Jurong Formation, where the Jurong Rock Caverns are located, is a testament to geological complexity. Dating back to the Late Triassic to Early Jurassic period, it is a sedimentary rock mass characterized by a heterogeneous mix of interbedded sandstone, siltstone, mudstone, and shale, with localized occurrences of limestone and dolomite.32 This interbedding means that layers of strong rock can be sandwiched with weak layers, creating unpredictable conditions for excavation.36

The structural geology of the Jurong Formation poses the most significant challenges. The formation has been subjected to intense tectonic activity, resulting in sharp folding, significant faulting, and a general NW-SE strike direction.39 This complex history means that rock mass quality can vary dramatically over very short distances, making detailed site investigation an absolute necessity.38 For the JRC, which features very large, wide-span caverns with flat roofs, the presence of low-angled bedding planes was a primary stability concern, as these planes can act as potential sliding surfaces.41 The design had to specifically account for the risk of structurally controlled failures, where blocks of rock could become detached along these pre-existing weaknesses.

Furthermore, the presence of limestone within the Jurong Formation introduces the risk of cavities and solution channels.36 These features, formed by the dissolution of the limestone by groundwater, can be of significant size and pose a serious hazard to both surface and subsurface construction. Experiences from other major projects in the Jurong Formation, such as the Pasir Panjang container port development, revealed difficulties with cavities extending to depths of 60 metres, requiring extensive ground treatment like jet grouting prior to construction.36 Although the rock mass at the JRC site has been hardened by regional and contact metamorphism with igneous dykes, which increases its overall strength, this does not negate the inherent risks posed by its structural complexity and variability.32

 

3.2 The Bukit Timah Granite (BTG): A Tale of Strength and Stress (UAF Site)

 

In stark contrast to the Jurong Formation, the Bukit Timah Granite, which hosts the Underground Ammunition Facility, is a much more homogenous and competent rock mass. This igneous intrusion, formed in the early Triassic period, consists mainly of granite and granodiorite.37 Its primary engineering advantage is its exceptional strength. The Unconfined Compressive Strength (UCS) of fresh Bukit Timah Granite is very high, averaging around 160 MPa and with values recorded in excess of 300 MPa.40 This inherent strength makes it an ideal host medium for excavating large, stable underground caverns.45

However, the BTG presents its own distinct set of geotechnical challenges, primarily related to its weathering profile and in-situ stress state. Deep tropical weathering, a process that has occurred over millions of years, has created a thick overburden of completely weathered granite and residual soil, which can extend to depths of over 60 metres.40 This necessitates the construction of deep access shafts to reach the competent, fresh rock required for cavern construction. The weathering process is not uniform, resulting in a highly undulating rockhead profile that often follows the surface topography.42

Two specific challenges arise from this weathering process. First is the presence of massive corestones or boulders, which are remnants of unweathered granite left “floating” within the decomposed residual soil matrix. These boulders, which can be over 6 metres in size, pose significant obstacles during shaft sinking and foundation excavation.42 Second, the granite is extremely abrasive. Laboratory tests have yielded a high Cerchar Abrasivity Index (CAI) of around 4.6, classifying the rock as “extremely abrasive”.42 This high abrasivity leads to rapid wear and tear on excavation tools, such as the disc cutters on Tunnel Boring Machines (TBMs) and drill bits, increasing maintenance time and cost.

Perhaps the most critical engineering characteristic of the Bukit Timah Granite is its high in-situ horizontal stress field. Measurements have consistently shown that the maximum horizontal stress is significantly higher than the vertical stress (due to overburden), with a ratio (K=σh​/σv​) of approximately 2 to 3.39 This high horizontal stress is highly beneficial for the stability of wide-span cavern roofs, as it creates a natural compressive arching effect that prevents tensile failure.49 However, this same high stress can lead to stress-induced instability, such as spalling or rock bursting, at the excavation face if not properly managed through careful blast design and sequencing.

The table below summarizes and contrasts the key geotechnical properties of these two critical rock formations.

Property	Bukit Timah Granite (BTG)	Jurong Formation (JF)
Rock Type	Igneous (Granite, Granodiorite) 37	Sedimentary (Sandstone, Siltstone, Mudstone, Limestone) 32
Intact Rock Strength (UCS)	High to Very High (Avg. ~160 MPa, up to >300 MPa) 40	Variable, but hardened by metamorphism. Generally lower than BTG.32
Rock Mass Quality (RQD/Q)	Generally Good to Extremely Good in fresh rock 43	Fair to Poor due to intense fracturing and interbedding of weak/strong layers 38
Key Structural Feature	4-5 well-defined joint sets, dominant sub-vertical NNW-SSE set 40	Intensely folded and faulted, with pervasive low-angle bedding planes 39
Primary Geotechnical Challenge	Deep weathering profile, large corestones, high abrasivity, high horizontal stress 40	High geological variability, interbedding of weak/strong rock, faults, potential for limestone cavities 33
In-Situ Stress (K = σh​/σv​)	High horizontal stress (K ≈ 2-3) 39	High horizontal stress (K ≈ 2), but more variable due to structural complexity 39
Permeability	Very low in intact rock (10⁻⁷ to 10⁻⁹ m/s), flow is dominated by fractures 40	Variable; higher permeability in fractured zones and along bedding planes 38

 

Section 4: The Engineering Blueprint: From Site Investigation to Stability Analysis

 

Translating the complex geological realities of Singapore into a safe, economical, and durable cavern design requires a systematic and multi-faceted engineering process. This process begins with an exhaustive characterization of the rock mass and culminates in a robust stability analysis that integrates empirical, analytical, and numerical methods. This section details the engineering blueprint used to design Singapore’s deep underground caverns.

 

4.1 Characterizing the Rock Mass: The Site Investigation (SI) Toolkit

 

Site investigation (SI) for a major cavern project is not a single event but a carefully phased campaign designed to progressively reduce geological uncertainty. The process typically unfolds in three stages: a preliminary phase for overall feasibility, a main phase for detailed design, and supplementary investigations during construction to address unexpected conditions.29

The SI toolkit combines a range of complementary techniques:

• Geophysical Surveys: The campaign begins with non-invasive surface geophysical methods, such as seismic refraction and reflection surveys and electrical resistivity tomography.29 These techniques provide a broad, macro-scale picture of the subsurface, helping to map the depth of the soil overburden, the elevation of the bedrock, and the locations of major geological structures like fault zones or weathered trenches.29 This initial mapping is crucial for siting the caverns and planning more detailed investigations.
• Exploratory Drilling: The cornerstone of direct investigation is drilling. This involves conventional soil boring through the overburden followed by diamond core drilling into the rock mass.29 Both vertical and inclined boreholes are used to retrieve continuous rock cores. These cores are invaluable, as they are meticulously logged to classify the rock mass (using systems like RQD and the Q-system) and provide physical samples for laboratory testing.49
• Horizontal Directional Coring (HDC): A pivotal innovation first employed in Singapore for the JRC project was HDC.29 Given that the JRC caverns were to be located beneath the seabed with limited surface access, traditional vertical drilling was impractical for investigating the specific cavern alignments. HDC utilizes a steerable core barrel to drill horizontally, allowing engineers to retrieve continuous rock cores directly along the planned tunnel and cavern axes, providing unparalleled insight into the ground conditions that would actually be encountered during excavation.29
• In-situ Testing: To understand the rock mass properties in their undisturbed, natural state, a suite of tests is conducted within the boreholes. These include packer tests (or Lugeon tests) to measure the permeability of the rock mass, hydraulic fracturing tests to determine the magnitude and orientation of the in-situ stresses, and advanced logging tools like borehole cameras and acoustic televiewers to precisely map the orientation, spacing, and condition of joints and fractures.29

 

4.2 Principles of Rock Cavern Design

 

The data gathered from the comprehensive SI campaign directly informs the fundamental principles of the cavern design.

• Optimizing Cavern Geometry and Orientation: A key principle in rock engineering is to align large underground openings to take maximum advantage of the in-situ stress field. In Singapore, where the horizontal stress is significantly higher than the vertical stress, caverns are ideally oriented with their long axis perpendicular to the direction of the maximum horizontal stress.49 This orientation allows the high compressive stress to form a stable arch over the cavern roof, minimizing tensile stresses and enhancing stability.
• Shaft and Access Design: In Singapore’s relatively flat terrain with thick soil overburden, the design of access shafts is a critical and challenging component.38 Shafts must first penetrate soft ground, which may include reclaimed sand fill and highly compressible marine clay, before reaching the competent bedrock below. The most common solution involves constructing the upper portion of the shaft using diaphragm walls or secant piles.55 These deep concrete walls serve a dual purpose: they act as the temporary retaining structure during excavation and as the permanent, watertight lining for the upper shaft, effectively cutting off groundwater from the soil layers.55
• Rock Support Philosophy: The design philosophy for caverns in competent rock is to rely on rock reinforcement rather than thick, costly concrete linings. The approach, often termed “Shotcrete Rock Reinforcement,” aims to mobilize and enhance the inherent strength of the surrounding rock mass to make it self-supporting.57 This involves a systematic application of rock bolts and shotcrete, tailored to the specific rock mass quality encountered.

 

4.3 A Multi-Pronged Approach to Stability Analysis

 

To ensure the long-term stability of the massive caverns, designers employ a combination of analytical methods, moving from empirical estimates to highly sophisticated numerical simulations.

• Empirical Methods (The Q-System): The Norwegian Geotechnical Institute’s Q-system is the workhorse for preliminary design and on-site support decisions.49 This empirical method provides a quantitative classification of the rock mass based on six parameters derived from core logging: the Rock Quality Designation (RQD), number of joint sets (
  Jn​), joint roughness (Jr​), joint alteration (Ja​), water inflow (Jw​), and the Stress Reduction Factor (SRF). The resulting Q-value is used in conjunction with charts to provide an initial estimate of the required rock support, such as the spacing of rock bolts and the thickness of shotcrete, for a given cavern span.49
• Numerical Modeling (FEM/DEM): For detailed design verification and optimization, numerical modeling is indispensable. Engineers use advanced software based on the Finite Element Method (FEM), such as Phase2 and FLAC3D, or the Distinct Element Method (DEM), such as UDEC and 3DEC.32

• FEM models treat the rock mass as a continuum and are excellent for analyzing stress redistribution and deformation around the cavern.59
• DEM models, like UDEC, are particularly powerful in jointed rock masses as they can explicitly represent individual discontinuities (joints and faults), allowing for the simulation of block sliding or rotation.41
• These models are used to simulate the entire excavation sequence, predict ground movements like crown settlement and wall convergence, analyze the performance of the proposed support system, and conduct sensitivity analyses to understand the impact of varying geological parameters.33

• Kinematic and Analytical Methods: In structurally controlled ground like the Jurong Formation, where failure is governed by the geometry of intersecting joints, kinematic analysis is crucial. Programs like UNWEDGE are used to identify all potentially unstable rock wedges that could be formed in the roof or walls of the cavern upon excavation.49 This analysis provides quantitative input for the design of the rock bolt pattern needed to secure these specific wedges. For the flat-roofed caverns of the JRC, analytical techniques based on the Voussoir beam analogy were also employed to assess the stability of the horizontally bedded rock layers acting as a natural flat arch.41

This integrated, multi-pronged approach—combining empirical rules of thumb, rigorous numerical simulation, and targeted analytical checks—provides a comprehensive and robust framework for cavern stability analysis, ensuring safety and optimizing design.

Phase	Technique/Method	Objective & Key Data Output	Relevant Snippets
1. Macro-Scale Site Characterization	Desk Study & Geophysical Surveys (Seismic, Electrical Resistivity)	Preliminary geological model, overburden depth, bedrock topography, location of major faults/weakness zones.	29
2. Micro-Scale Site Characterization	Exploratory Drilling (Vertical, Inclined, HDC) & Core Logging	Rock cores for lab tests, Rock Mass Classification (RQD, Q-value), discontinuity data. HDC for sub-seabed alignments.	29
3. In-Situ Property Measurement	Borehole Testing (Packer, Hydraulic Fracturing, Acoustic Imaging)	Permeability, in-situ stress magnitude and orientation, joint orientation and properties.	29
4. Material Property Measurement	Laboratory Testing (UCS, Triaxial, Point Load, CAI)	Intact rock strength (c, φ), stiffness (E), tensile strength, abrasivity.	42
5. Preliminary Support Design	Empirical Analysis (Q-System)	Initial estimation of rock support requirements (rock bolts, shotcrete) based on rock mass quality and cavern size.	49
6. Detailed Design & Verification	Numerical Modeling (FEM/DEM: UDEC, FLAC3D, Phase2) & Kinematic Analysis (UNWEDGE)	Verification of support design, prediction of deformation, analysis of excavation sequence, stability analysis of structural wedges.	32

 

Section 5: The Art of Excavation and Support

 

The transition from a digital blueprint to a physical subterranean space is a complex orchestration of heavy machinery, controlled energy, and precision engineering. This section delves into the practical methods of excavation and support used to construct Singapore’s rock caverns, highlighting key innovations that have enhanced safety, efficiency, and the ability to manage the challenging underground environment.

 

5.1 Excavation: The Drill-and-Blast Method

 

For the creation of large, non-circular caverns in the hard rock formations of Singapore, the conventional drill-and-blast method is the technique of choice.62 While Tunnel Boring Machines (TBMs) are used extensively for Singapore’s linear MRT and utility tunnels, their fixed circular profile and high capital cost make them impractical for excavating the vast, cathedral-like spaces of the UAF and JRC.49 Drill-and-blast offers the flexibility needed to create custom cavern shapes and sizes in variable rock conditions.64 The process involves drilling a precise pattern of holes into the rock face, loading them with explosives, and detonating them in a controlled sequence to break the rock, which is then removed (a process called mucking).65

A critical innovation that revolutionized this process in Singapore was the adoption of on-site bulk emulsion explosive technology, used in both the UAF and JRC projects.49 Traditionally, excavation would rely on pre-packaged explosives, which come with significant logistical and safety challenges related to transportation and storage, especially in a densely populated urban state with stringent regulations. The bulk emulsion system, such as the Civec™ Drive system used at the JRC, circumvents these issues.66 It involves the on-site storage of two separate, non-explosive chemical components. These components are pumped to the excavation face and mixed in the charging unit only at the moment they are loaded into the drill holes, creating the explosive product at the point of use. This “just-in-time” approach dramatically enhances safety, as large quantities of Class 1 explosives do not need to be stored on-site.49 It also yields major productivity gains. At the JRC, this system reduced the explosives cost by 21%, improved charging time per hole by 63%, and cut manpower requirements for charging by 25% compared to manual charging with packaged explosives.66

Controlling the side effects of blasting, particularly ground vibrations, is a key performance requirement.49 To manage this, project teams conduct initial test blasts to develop site-specific models of how ground shock propagates through the local geology. During full-scale production, a network of monitoring stations continuously measures vibration levels to ensure they remain within safe, permissible limits for surrounding structures and the public.49

 

5.2 Primary Rock Support: The Synergy of Bolts and Shotcrete

 

Once a section of the cavern is excavated, immediate support is installed to ensure stability. The prevailing philosophy in Singapore’s hard rock caverns is the “Shotcrete Rock Reinforcement” (SRR) concept, which creates a composite structure that mobilizes the rock’s own inherent strength.57 This system is a synergistic combination of rock bolts and shotcrete.

• Rock Bolts: Rock bolts are the primary structural reinforcement element, acting like nails to hold the rock mass together.64 They are installed in a systematic pattern drilled into the cavern roof and walls. By tensioning the bolts (in the case of active bolts) or grouting them into place (for passive bolts), a zone of compression is created in the rock immediately surrounding the opening.57 This confining pressure increases the frictional strength along rock joints, prevents the loosening and unraveling of the rock mass, and effectively transforms the fractured rock into a stronger, composite reinforced arch.57 The length, spacing, and capacity of the bolts are determined by the rock mass quality (from the Q-system) and the analysis of potential structural wedges.49
• Shotcrete: While rock bolts secure larger blocks of rock, shotcrete is applied to manage the rock surface between the bolts.57 Shotcrete is concrete that is pneumatically projected at high velocity onto the rock face, forming a thin “protective skin”.57 Often reinforced with steel or synthetic fibres, this layer serves several critical functions: it prevents small, structurally-controlled wedges from falling out between bolts, it helps to distribute stresses more evenly across the rock surface, and it protects the rock from deterioration due to air and moisture.52 The development of performance-based specifications and testing methods, such as the Round Determinate Panel (RDP) test, has been crucial in ensuring the quality and post-crack ductility of modern fibre-reinforced shotcrete linings.67

 

5.3 The Critical Challenge: Water Control and Grouting

 

Managing groundwater ingress is one of the most significant challenges in deep underground construction, particularly in fractured rock masses or when excavating below the seabed, as was the case for the JRC.9 Uncontrolled water inflow can compromise safety, hinder excavation progress, and lead to long-term operational issues.

The primary strategy employed is proactive water control through systematic pre-grouting.49 This “probe and grout” method involves drilling a fan of long probe holes ahead of the advancing excavation face. If these holes intersect water-bearing fractures or fault zones (indicated by significant water inflow), the excavation is paused. A pattern of grout holes is then drilled around the area, and a grout mixture (typically cement-based) is injected under pressure to seal the fissures in the rock mass. The effectiveness of the grouting is checked with control holes before excavation resumes.49 This preventative approach is far more effective and economical than trying to manage large water inflows after they have occurred.

The JRC project takes this hydrogeological management to a new level with its operational water curtain system. This is a permanent feature designed for the long-term containment of the stored hydrocarbons.9 It consists of a network of dedicated water curtain galleries excavated above and between the main storage caverns. From these galleries, an array of boreholes is drilled into the surrounding rock mass. Water is continuously circulated through this system to artificially maintain a high groundwater pressure field around the caverns.33 This ensures that the hydraulic potential of the groundwater is always greater than the pressure exerted by the stored oil. This pressure differential guarantees that the net direction of any seepage will always be from the rock mass

into the cavern, where it can be safely collected in sumps and pumped to the surface.9 This innovative approach harnesses a natural principle—hydrostatic pressure—to provide a robust, self-healing containment barrier, eliminating the need for a costly and fallible man-made liner.

The vast scale of grouting at the JRC generated an enormous dataset. This has enabled a shift in grouting from a practice heavily reliant on experience—often called a “black art”—towards a more data-driven science. Researchers have used this data to train Artificial Neural Network (ANN) models to predict the required grout volume for a given section of tunnel based on its measured rock mass properties (like RMR, Q-index, and permeability).68 Such tools have the potential to significantly improve the efficiency and predictability of grouting operations in future projects.

 

Section 6: Lessons Learned and the Future Frontier

 

Singapore’s journey into the depths has yielded more than just new space; it has produced a wealth of engineering knowledge, project management experience, and a bold vision for the future. The lessons learned from the UAF and JRC are now informing the next generation of subterranean development, which is poised to move beyond discrete projects towards an integrated, digitally managed underground urban system.

 

6.1 Critical Lessons from a Decade of Digging

 

The successful completion of Singapore’s pioneering cavern projects was built on several key principles and learnings that now form the bedrock of its rock engineering practice.

• The Value of Geotechnical Baselines: A major lesson in project and risk management was the effective use of a Geotechnical Baseline Report (GBR) for the JRC project.49 The GBR establishes a contractually agreed-upon interpretation of the subsurface conditions that can be expected. This provides a clear and fair basis for pricing the work and, more importantly, for assessing and compensating for unforeseen ground conditions encountered during construction. This approach fosters a more collaborative relationship between the client and contractor and helps to avoid costly disputes.49
• Integrated Engineering and Planning: The complexity of cavern development demands a tightly integrated, multi-disciplinary approach from the very beginning. Success hinges on the close collaboration of geologists, rock mechanics specialists, numerical modelers, and construction technologists throughout the project lifecycle, from initial site selection and investigation to final design and monitoring.49 This holistic perspective ensures that design decisions are grounded in geological reality and construction practicalities.
• The Power of Performance Monitoring: Comprehensive instrumentation and monitoring are not optional extras but essential components of the design and construction process. The use of instruments like multi-point borehole extensometers (MPBX), convergence arrays, and load cells on rock bolts provides real-time data on the performance of the excavation and support systems.49 This data is vital for validating the assumptions made in the design models and allows for the optimization of support measures on the fly. For instance, monitoring at the UAF revealed that rock bolt loads were generally low, suggesting that the support system could be optimized in future designs due to the favorable high horizontal stresses.49
• Innovation as a Strategic Necessity: Singapore’s cavern projects have been defined by innovation born out of necessity. From the first-time use of Horizontal Directional Coring (HDC) to investigate sub-seabed geology 29, to the adoption of safer and more productive bulk emulsion explosives 66, to the elegant hydrogeological solution of the water curtain containment system 9, technological and conceptual innovation has been the key to overcoming the unique challenges of building deep and large caverns in Singapore’s complex urban and geological environment.

 

6.2 The Future is Down: Emerging Applications

 

Building on the success of the UAF and JRC, Singapore’s URA Master Plan envisions a future where a diverse range of infrastructure is housed underground, creating a multi-functional subterranean landscape.

• Underground Data Centers: This is one of the most promising future applications. The demand for data center capacity is growing exponentially, but these facilities are land-hungry and energy-intensive. Placing data centers underground offers enhanced physical security from surface threats and, crucially, significant potential for energy savings.70 The stable, cool ambient temperature of the deep underground environment can dramatically reduce the energy required for cooling, which is a major operational cost for data centers. This aligns perfectly with Singapore’s Green Data Centre Roadmap, which prioritizes energy efficiency.71 Companies like Keppel Data Centres are already actively exploring the feasibility of developing underground facilities.70
• Underground Reservoirs and Drainage: To enhance climate resilience and water security, national water agency PUB is studying the feasibility of using large rock caverns for stormwater storage.2 This would involve channeling excess rainwater from storms into deep underground reservoirs, mitigating surface flooding. The concept could also be integrated with a pumped-storage hydropower system, where water is pumped up during off-peak hours and released to generate electricity during peak demand, creating a large-scale energy storage solution.26
• Automated Logistics and Warehousing: The Master Plan includes studies for an underground goods movement system, potentially linking the new Tuas Mega Port with inland industrial estates like Jurong and Tanjong Kling.26 Such a system could use automated guided vehicles or conveyor belts running through a network of tunnels to move cargo, drastically reducing heavy truck traffic on surface roads, thereby easing congestion and improving air quality. Similarly, underground caverns are being considered for large-scale warehousing and logistics facilities.74

 

6.3 Enabling the Next Generation: Digitalization and Policy

 

Realizing this ambitious vision for a subterranean city requires more than just advanced engineering; it requires sophisticated planning tools and a supportive policy environment.

• Digital Twins and 3D Modeling: The future of urban planning is digital. Singapore is at the forefront of this with its “Digital Underground” project, part of the larger “Virtual Singapore” initiative.25 This program aims to create a comprehensive, integrated 3D digital twin of the nation’s subsurface. By using technologies like Building Information Modelling (BIM) and Geographic Information Systems (GIS) to capture and map all underground assets—from deep caverns to shallow utilities—planners can visualize and manage this complex, invisible space. This digital ecosystem is critical for enabling coordinated planning, avoiding conflicts between different underground developments, and optimizing the use of this finite resource.25
• Proactive Legal and Policy Framework: Recognizing that legal ambiguity could hinder development, Singapore has proactively updated its legislation. Amendments to the State Lands Act, for instance, clarify that private land ownership extends only to a certain depth (typically 30 metres), with the state owning the deep subterranean space below.7 This forward-thinking policy provides the government with the legal clarity needed to plan and acquire tracts of deep underground land for large-scale infrastructure projects without impeding surface property rights, a crucial enabler for the Underground Master Plan.
• The Human Factor: While the technical feasibility of moving industries and utilities underground is well-established, public perception and acceptance remain a potential barrier for any future applications that involve human occupation.24 The idea of underground living spaces, for example, faces significant psychological hurdles related to claustrophobia and the lack of natural light and ventilation.7 While technology can simulate natural light and provide fresh air, overcoming these deep-seated human preferences will require extensive public consultation, education, and a focus on creating high-quality, human-centric designs that are attractive and liveable.24

Ultimately, Singapore’s journey underground is evolving. It is moving beyond the construction of impressive, but discrete, cavern projects and is now focused on creating a truly integrated, multi-functional subterranean urban system. This next phase is less about the brute force of excavation and more about the sophisticated management of a complex system, orchestrated through a national digital ecosystem and guided by a long-term strategic vision. This represents the next stage of maturity in Singapore’s quest to conquer its final frontier.

Works cited

1. Jurong Rock Caverns – – Singapore Good Design Awards, accessed June 25, 2025, https://sgmark.org/winners/jurong-rock-caverns/
2. Is the future of cities underground? Singapore thinks so – create digital, accessed June 25, 2025, https://createdigital.org.au/future-of-cities-underground-singapore/
3. Advances and Challenges in Underground Space Use in Singapore – Digital Object Identifier, accessed June 25, 2025, https://doi.nrct.go.th/admin/doc/doc_652223.pdf
4. (PDF) Advances and challenges in underground space use in Singapore – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/publication/308161148_Advances_and_challenges_in_underground_space_use_in_Singapore
5. ROCK CAVERN SPACE DEVELOPMENT IN SINGAPORE (keynote paper) – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/publication/283464200_ROCK_CAVERN_SPACE_DEVELOPMENT_IN_SINGAPORE_keynote_paper
6. The Business Times – Singapore planning a subterranean future as it faces space constraints – SP Group, accessed June 25, 2025, https://www.spgroup.com.sg/dam/spgroup/wcm/connect/spgrp/6b5653a3-f054-429f-96ff-b78f18d10693/The+Business+Times+-+Singapore+planning+a+subterranean+future+as+it+faces+space+constraints.pdf?MOD=AJPERES&CVID=
7. Singapore Is Creating a Subterranean Master Plan – Next City, accessed June 25, 2025, https://nextcity.org/urbanist-news/underground-city-movement-singapore-helskini
8. Uncovering the Underground – Centre for Liveable Cities Singapore, accessed June 25, 2025, https://www.clc.gov.sg/events/lecture/underground-space-for-a-liveable-singapore
9. Jurong Rock Caverns – CTRL Your Future, SHIFT Your Perspectives, accessed June 25, 2025, https://www.ctrlshift.gov.sg/engineering-marvels/jurong-rock-caverns/
10. Jurong Rock Caverns | JTC, accessed June 25, 2025, https://www.jtc.gov.sg/find-space/jurong-rock-caverns
11. Jurong Rock Caverns officially opens 2 Sep 2014 – If Only Singaporeans Stopped to Think, accessed June 25, 2025, https://ifonlysingaporeans.blogspot.com/2014/09/jurong-rock-caverns-officially-opens.html
12. PM Lee Hsien Loong at the Official Opening of the Jurong Rock Caverns – Prime Minister’s Office Singapore, accessed June 25, 2025, https://www.pmo.gov.sg/Newsroom/transcript-prime-minister-lee-hsien-loongs-speech-official-opening-jurong-rock-caverns
13. Jurong Rock Caverns Singapore, accessed June 25, 2025, https://jrcsingapore.com/
14. Jurong Rock Caverns – Singapore, accessed June 25, 2025, https://surbanajurong.com/sector/jurong-rock-caverns/
15. Underground Ammunition Storage Facility – SG101, accessed June 25, 2025, https://www.sg101.gov.sg/resources/connexionsg/singaporesfirst-underground-ammo-storage-facility/
16. 1 Proposed Updates to the Siting Criteria of Heavy Earth Cover Magazines K.W. Kang; Defence Science and Technology Agency, accessed June 25, 2025, https://ndia.dtic.mil/wp-content/uploads/2018/intexpsafety/OhPaper.pdf
17. Safe Storage of Ammunition Underground | PDF, accessed June 25, 2025, https://www.scribd.com/document/711495223/Safe-Storage-of-Ammunition-Underground
18. efence Science & Technology Agency (DSTA) created new safety standards with the development of Singapore’s first Underground Ammunition Facility (UAF) – INNOVATION magazine, accessed June 25, 2025, http://www.innovationmagazine.com/volumes/v3n2/features1.html
19. Singapore to Unveil Rigorous Underground Master Plan 2019, accessed June 25, 2025, https://construction-property.com/singapore-to-unveil-rigorous-underground-master-plan-2019/
20. Master Plan 2019 Underground Structure layer | URA | data.gov.sg, accessed June 25, 2025, https://data.gov.sg/collections/1751/view
21. Digging deep: Singapore plans an underground future – Thomson Reuters Foundation News, accessed June 25, 2025, https://news.trust.org/item/20181224005446-fqbc3
22. Singapore Unveils Underground Space Usage Plans for 3 Pilot Areas – Orissa International, accessed June 25, 2025, https://www.orissa-international.com/business-news/singapore-unveils-underground-space-usage-plans-for-3-pilot-areas/
23. How To Understand URA Master Plan Singapore 2024 – Full Guide! – DollarBack Mortgage, accessed June 25, 2025, https://dollarbackmortgage.com/blog/understand-ura-master-plan/
24. Is the future of Singapore underground? – Lee Kuan Yew School of Public Policy, accessed June 25, 2025, https://lkyspp.nus.edu.sg/gia/article/is-the-future-of-singapore-underground
25. Singapore goes deep with digital underground project, accessed June 25, 2025, https://ibtekr.org/en/cases/singapore-is-heading-deep-into-a-project-to-digitize-the-ground/
26. Digging deep in Singapore for space solutions | The Straits Times, accessed June 25, 2025, https://www.straitstimes.com/singapore/digging-deep-in-singapore-for-space-solutions
27. Singapore’s Underground Ammunition Facility – DEFENSE STUDIES, accessed June 25, 2025, http://defense-studies.blogspot.com/2010/08/singapores-underground-ammunition.html
28. A Deep Dive into Manmade Tunnels and Caverns Underground in the City-State – BiblioAsia, accessed June 25, 2025, https://biblioasia.nlb.gov.sg/files/pdf/Vol%2018/Issue%202/v18-issue2_Underground.pdf
29. Rock Engineering Practice for Development of Underground Caverns in Singapore – ISSMGE: Heritage Time Capsule (HTC) Project, accessed June 25, 2025, https://htc.issmge.org/uploads/contributions/L10-rock-engineering-practice-for-development.pdf
30. Build Me Something Better: Ep 2 [Underground Ammunition Facility] – YouTube, accessed June 25, 2025, https://www.youtube.com/watch?v=qe4GpmYwCkk
31. Jurong Rock Caverns – Wikipedia, accessed June 25, 2025, https://en.wikipedia.org/wiki/Jurong_Rock_Caverns
32. JTC’s Jurong Underground Storage Caverns—Singapore – Agapito Associates, accessed June 25, 2025, https://www.agapito.com/portfolio-posts/jtcs-jurong-underground-storage-caverns-singapore/
33. Stability Analysis of Underground Storage Cavern Excavation in Singapore | PDF | Strength Of Materials | Stress (Mechanics) – Scribd, accessed June 25, 2025, https://www.scribd.com/document/520783264/1-s2-0-main
34. Rock Cavern in Singapore | PDF | Tunnel – Scribd, accessed June 25, 2025, https://www.scribd.com/document/430530108/Rock-cavern-in-Singapore
35. The Secret Underground World Of Singapore – CITI I/O, accessed June 25, 2025, https://citi.io/2017/10/09/the-secret-underground-world-of-singapore/
36. Geotechnical Aspects of Container Port … – Surbana Jurong, accessed June 25, 2025, https://surbanajurong.com/wp-content/uploads/2018/08/2018_Geotechnical-Aspects-of-Container-Port-Development-24072018.pdf
37. Geology of Singapore – Wikipedia, accessed June 25, 2025, https://en.wikipedia.org/wiki/Geology_of_Singapore
38. Underground Space Development in Singapore Rocks | PDF | Geology | Tunnel – Scribd, accessed June 25, 2025, https://www.scribd.com/document/253143808/Underground-Space-Development-in-Singapore-Rocks
39. INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING – ISSMGE, accessed June 25, 2025, https://www.issmge.org/uploads/publications/25/26/ISC5_162.pdf
40. Geology of Singapore, accessed June 25, 2025, https://www.srmeg.org.sg/docs/N13072012_2.pdf
41. Multi-approach stability analyses of large caverns excavated in low-angled bedded sedimentary rock masses in Singapore | Request PDF – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/publication/333382175_Multi-approach_stability_analyses_of_large_caverns_excavated_in_low-angled_bedded_sedimentary_rock_masses_in_Singapore
42. Construction Challenges in Bukit Timah Granite Formation – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/profile/Veeresh-Chepurthy/publication/309575353_Construction_Challenges_in_Bukit_Timah_Formation/links/58182a9c08aeffbed6c34765/Construction-Challenges-in-Bukit-Timah-Formation.pdf
43. Rock Engineering for an Underground Storage Facility in Singapore …, accessed June 25, 2025, https://www.srmeg.org.sg/docs/Rock%20engineering%20-%20NUS%20Lecture%20Sept%2006%20(Handout).pdf
44. Variability of Mechanical and Physical Properties of Singapore Bukit Timah Granite Rocks and Residual Soils – OnePetro, accessed June 25, 2025, https://onepetro.org/ISRMARMS/proceedings-pdf/ARMS1018/All-ARMS1018/ISRM-ARMS10-2018-031/1162254/isrm-arms10-2018-031.pdf
45. Engineering geology of the Bukit Timah Granite for cavern construction in Singapore, accessed June 25, 2025, https://www.lyellcollection.org/doi/10.1144/gsl.qjegh.1995.028.p2.06
46. Geotechnical Feasibility of Rock Cavern Construction in the Bukit Timah Granite of Singapore – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/publication/284907591_Geotechnical_Feasibility_of_Rock_Cavern_Construction_in_the_Bukit_Timah_Granite_of_Singapore
47. Engineering geology of the Bukit Timah Granite for cavern construction in Singapore, accessed June 25, 2025, https://www.lyellcollection.org/doi/abs/10.1144/gsl.qjegh.1995.028.p2.06
48. Effect of Rock Abrasiveness on Wear of Shield Tunnelling in Bukit Timah Granite – MDPI, accessed June 25, 2025, https://www.mdpi.com/2076-3417/10/9/3231
49. Rock Engineering Practice for Development of Underground Caverns in Singapore, accessed June 25, 2025, https://www.researchgate.net/publication/321480353_Rock_Engineering_Practice_for_Development_of_Underground_Caverns_in_Singapore
50. Hydrogeology of Bukit Timah Granite | PDF – Scribd, accessed June 25, 2025, https://www.scribd.com/doc/236713061/Hydrogeology-of-Bukit-Timah-Granite
51. Rock Investigation Planning for Rock Cavern Development – Society for Rock Mechanics & Engineering Geology (Singapore), accessed June 25, 2025, https://srmeg.org.sg/docs/GeologyWorkshop_Dr_Cai_Jun_Gang.pdf
52. Probabilistic assessment of engineering rock properties in Singapore for cavern feasibility, accessed June 25, 2025, https://dspace.mit.edu/handle/1721.1/99604
53. Rock Mechanics and Rock Cavern Design_ICE HKA | PPT – SlideShare, accessed June 25, 2025, https://www.slideshare.net/slideshow/rock-mechanics-and-rock-cavern-designice-hka-70189880/70189880
54. The Jurong Rock Caverns (JRC) under construction (Courtesy of JTC and SINTEF-TritechMulticonsult Consortium). – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/figure/The-Jurong-Rock-Caverns-JRC-under-construction-Courtesy-of-JTC-and_fig1_336115716
55. Design and construction of shaft for rock caverns in … – Techno Press, accessed June 25, 2025, http://techno-press.org/download.php?journal=gae&volume=13&num=1&ordernum=10
56. Design and construction of shaft for rock caverns in Singapore – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/publication/318777563_Design_and_construction_of_shaft_for_rock_caverns_in_Singapore
57. Practical shotcrete rock reinforcement for hard rock openings – HKIE, accessed June 25, 2025, https://www.hkie.org.hk/hkietransactions/upload/2021-09-27/practical_shotcrete.pdf
58. Construction of Underground Roads and Tunnels Beneath Sensitive Infrastructures in Singapore – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/publication/385171214_Construction_of_Underground_Roads_and_Tunnels_Beneath_Sensitive_Infrastructures_in_Singapore
59. Sustainable Development in Singapore’s Underground Urban Landscape: Innovations and Strategies for a Greener Future, accessed June 25, 2025, https://www.ies.org.sg/Tenant/C0000005/PDF%20File/TC/Sustainable%20Development%20in%20Singapore’s%20Underground%20Urban%20Landscape%20Innovations%20and%20Strategies%20for%20a%20Greener%20Future%20(6).pdf
60. Numerical Modeling in Geotechnical Practice – College of Design and Engineering – National University of Singapore, accessed June 25, 2025, https://cde.nus.edu.sg/cee/wp-content/uploads/sites/7/2020/09/WohHupDistinguishedLectures-HonoraryProfHarryTanSiewAnn.pdf
61. Analysis of rock cavern stability | NTU Singapore, accessed June 25, 2025, https://dr.ntu.edu.sg/handle/10356/71351
62. Rock Cavern in Singapore | PDF | Tunnel – Scribd, accessed June 25, 2025, https://fr.scribd.com/document/430530108/Rock-cavern-in-Singapore
63. Development of Underground Rock Caverns for Storage of Liquid …, accessed June 25, 2025, https://awards.ita-aites.org/images/Proceedings/2016/8-Jurong-Rock-Caverns.pdf
64. Services – Asia Tunnelling & Construction Pte Ltd, accessed June 25, 2025, https://www.asiatunnelling.com/services
65. Guide to Cavern Engineering – Hong Kong – CEDD, accessed June 25, 2025, https://www.cedd.gov.hk/filemanager/eng/content_112/eg4_20180102.pdf
66. Improving charge time and reducing cost – Orica, accessed June 25, 2025, https://www.orica.com/ArticleDocuments/2603/200197_Case%20Study_Improving%20charge%20time%20and%20reducing%20cost_English.pdf.aspx?OverrideExpiry=Y
67. ITA/AITES REPORT 2006 on Shotcrete for rock support A summary report on state-of-the-art, accessed June 25, 2025, https://about.ita-aites.org/publications/wg-publications/download/157_bffc84d4e442d410256e92cdcaca31da
68. Grouting in rock cavern : a case study – DR-NTU, accessed June 25, 2025, https://dr.ntu.edu.sg/entities/publication/32cc0465-6965-4a3d-b15c-84fae4659a2c
69. Grouting in rock cavern : a case study – DR-NTU, accessed June 25, 2025, https://dr.ntu.edu.sg/entities/publication/4cbca064-87fb-4776-a898-447abb983d6a
70. Land restrictions force Singapore’s data centers underground & up high, accessed June 25, 2025, https://datacenternews.asia/story/land-restrictions-force-singapores-data-centers-underground-high
71. Singapore’s Green Data Centre Roadmap – Representing a Necessary Intersection between Digital Infrastructure and Sustainability | Insights | Mayer Brown, accessed June 25, 2025, https://www.mayerbrown.com/en/insights/publications/2024/08/singapores-green-data-centre-roadmap-representing-a-necessary-intersection-between-digital-infrastructure-and-sustainability
72. Underground caverns could solve flooding woes | News | Eco-Business | Asia Pacific, accessed June 25, 2025, https://www.eco-business.com/news/underground-caverns-could-solve-flooding-woes/
73. Summary of Major Underground Infrastructure Projects in Singapore – ResearchGate, accessed June 25, 2025, https://www.researchgate.net/figure/Summary-of-Major-Underground-Infrastructure-Projects-in-Singapore_tbl2_308161148
74. URA Draft Master Plan 2025 unveils new housing in Dover, Defu, Newton and Paterson, accessed June 25, 2025, https://m.economictimes.com/news/international/singapore/ura-draft-master-plan-2025-unveils-new-housing-in-dover-defu-newton-and-paterson/articleshow/122063939.cms
75. Developing Underground Space: A View From Singapore – WSP, accessed June 25, 2025, https://www.wsp.com/en-us/insights/developing-underground-space-a-view-from-singapore