Tunnels provide the networks and connections that underpin much of our lives. From water, sewer, cables and utilities to high speed rail, metros, roads, mines, science projects and industry, they connect us with vital resources, services and each other.

Today, the underground environment we used to rely on to take congestion off our city streets is as busy and congested as life above ground. Arup designs complex tunnel schemes that navigate this underground world, aligning both climate and cost imperatives, and exploring ways to reduce the resources and materials used in construction.

Beyond the core tunnel disciplines of civil engineering, architecture, geotechnics, machinery and soil mechanics, our global team includes experts in ventilation, lighting, MEP, acoustics, fire, drainage, safety and public health. Our approach – ‘total tunnel design’ – integrates all the relevant disciplines leading to lower-risk and more efficient, effective and affordable designs. This approach makes projects more sustainable, reducing excavation and materials by effective space proofing and lining system optimisation and introducing innovations such as extracting heat from tunnel linings.

How we can help you

Fire safety

Planning and designing robust fire safety in tunnels.

Fire safety

Fire safety is a key consideration underground. Tunnels require evacuation routes for occupants, emergency ventilation, fire suppression systems, and structural fire protection to prevent extensive damage to the tunnel. 

The four new stations we worked on as part of the Second Avenue Subway were some of the largest underground excavations in North America.

Our fire team is recognised as a world leader. By including their detailed insights and innovative solutions into fire risks and mitigation within our tunnel designs, we have been able to greatly reduce the costs and time of our many construction projects. 

For decades Arup has worked with owners, operators, and regulators to develop world-class solutions to tunnel fire safety challenges. Through recognition of the needs and aspirations of our clients, we develop innovative, integrated solutions which deliver value, performance, and durability. We sit on technical committees to further the development of tunnel fire safety standards. Our team has delivered design solutions in some of the world's most challenging environments, such as New York City’s Second Avenue Subway, UK's Channel Tunnel Rail Link, and Kuala Lumpur's STAR light rail system. 

Find out more about our fire engineering expertise

Ground movements and building impacts

Geotechnical expertise and analysis for tunnels, buildings and utilities infrastructure.

Ground movements and building impacts

Our geotechnical expertise and powerful in-house software tools are vital in ensuring tunnel safety and the integrity of other infrastrucutre.

Crossrail tunnelling taking place

Tunnelling activity underway on London's Crossrail

We deliver deliver rigorous settlement analysis, as well as impact assessments for existing buildings and utilities infrastructure, to assure safe and efficient construction.

For London's Crossrail we worked in joint venture with Atkins, designing the 42km of new tunnels under central London that were constructed in just over three years. Our work included the detailed design of the tunnels as well as an assessment of the impact that such significant tunnelling and excavation works could have on surrounding structures. 

Early on, we identified the need for a comprehensive digital GIS platform to manage the vast amount of geotechnical, land and site data that would be involved. Using this data, we navigated major infrastructure and utilities below ground, identifying possible obstructions during tunnelling, while flagging buildings that were at greater risk above to refine the tunnel alignment. 

Find out more about our work on Crossrail's tunnels

Inspection and maintenance

Effective monitoring, issue identification and maintenance.

Inspection and maintenance

The ability to easily monitor tunnels and spot potential issues early is a key aspect of a successful maintenance regime.

Loupe 360 tunnel inspection cgi

Arup's Loupe 360 allows for the automation of tunnel inspections

We have developed a tunnel inspection, visualisation and analytics platform that allows asset owners, maintainers and decision makers to remotely assess the condition and behaviour of their tunnel systems.

Our Loupe 360 platform provides 360-degree imagery and computer vision, to enable rich visualisation and asset analysis, supported by machine learning defect detection, inventorying and condition ratine analytics. 

Find out more about Loupe 360


An integrated approach to system design and implementation.


Our Total Tunnel Design approach means that systems – their installation, maintenance and replacement – are an integral part of our designs, not an inconvenient afterthought.

As well as ventilation and fire, our design team includes experts in signaling, lighting, electricity, telephony, drainage and MEP.


Controlling temperature, air quality and experience.


Ventilation systems can undermine the feasibility of tunnel projects.

Arup has provided tunnel ventilation in highly built-up areas such as New York’s Second Avenue Subway. We guide our clients to help solve highly complex technical challenges as well as using less intrusive equipment that can be used for multiple purposes.

We try to harness natural ventilation where possible, or – going beyond design codes – use sophisticated modelling to unlock efficient yet affordable designs. 

Today’s ventilation systems need to be adaptable for a rapidly-changing transport environment. The mass use of electric vehicles is being mandated by many developed jurisdictions, leading to new considerations for tunnel ventilation and safety. Arup is helping clients prepare for the future.

Digital tools

Our team works with simpler 1D models or advanced Computational Fluid Dynamics 3D tools as well as our own agent-based modelling tool – Arup Mass Motion – to better understand both human behaviour and activity, as well as the physics of ventilation in tunnel environments during emergencies. These insights allow us to accurately plan for evacuation scenarios from a tunnel affected by fire smoke and identifying – for example - where people will be able to exit underneath smoke caused by fire. 

Applying this data-driven, quantitative analysis of risk early on helps us establish a realistic, performance-based view of ventilation requirements even at concept design stage.

Influencing tunnelling standards

Tunnel vent design is rightly driven by safety standards that take account of both normal operations and rare eventualities such as fire. Simply following codes can impose the inclusion of huge systems, fans and vents that will rarely – if ever – be used. As co-authors on many of the global committees that publish tunnel ventilation standards, we understand the intent of these codes, and create lower-impact answers that deliver the required performance.

Crossrail tunnel between Royal Oak and Farringdon
Learning from our work on HS1, we helped develop the tunnelling strategy for Crossrail, reducing the number of tunnel boring machines required.
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Tunnel types

Cut and cover

Cut and cover

We combine our structural geotechnical expertise to create efficient cut-and-cover tunnel designs for a wide range of subsurface structure, including stations and portals. Where possible, we integrate the initial support system with the permanent structure.

Immersed tunnels

Immersed tunnels

We plan, design and oversee some of the world’s most complex immersed tunnel projects.

Fehmarnbelt Fixed Link - an immersed tunnel to link Denmark to Germany in Northern Europe’s largest infrastructure project

The breadth of our tunnelling and engineering disciplines allows us to integrate the many interrelated aspects of tunnels in this challenging environment; from environmental management, dredging, foundation and protection works to structure/joints and MEP services.

Arup is part of a JV delivering the Fehmarnbelt Fixed Link immersed tunnel that will link Denmar and Germany - and is scheduled for completion in 2029. The unique scale of this immersed tunnel required an innovative design approach. Thinking out of the box, the work by our JV made the selection of the immersed tunnel option preferable over the cable-stayed bridge, backed by our thorough analysis of technical, environmental, risk, safety, and economic factors.

The advantages of building a tunnel included lower risks to navigational safety and lower permanent impact on the marine environment and bird migration in the region. Our tunnel ventilation strategy was also key to selecting a tunnel over a bridge.

Mined tunnels

Mined tunnels

Our diverse global team of mined tunnelling experts takes projects from concept, detailed design and construction right through to end-of-life and reuse.

Their experience spans railway and metro tunnels to the complex deep cavern networks of mining and sewerage storage. 

As well as understanding practical construction issues, we use our own in-house mined tunnel optimiser tools and BIM to create a single source of truth for everyone involved in these complex projects.



Rock mechanics – understanding the characteristics and behaviour of rock masses and the support systems necessary to efficiently support them – is a science in its own right.

Long Baseline Neutrino Facility

The Long Baseline Neutrino Facility In Lead, South Dakota

We apply that science to ambitious and complex projects in transportation, energy, science and mining. 

Our team uses advanced modelling tools to accurately determine the response of different rock types to external forces, enabling us to design safe, efficient and cost-effective excavation plans.

Learn about our work tunnelling the caverns required for the USA’s Long Baseline Neutrino Facility – one of the world’s most significant big science projects.

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TBM tunnels

TBM tunnels

Every segmentally-lined tunnel has its own challenges.

Tunnel part of the Hong Kong Zhuhai Crossing

The Tuen Mun Chek Lap Kok Link provides a strategic linkage between the Northwest New Territories and the Hong Kong Boundary Crossing Facilities (HKBCF), the North Lantau and the Hong Kong International Airport (HKIA).

From the smallest water conveyance tunnel to the largest vehicular and metro tunnels, we are skilled at marrying project goals with the known capabilities of tunnel boring machines. Beyond traditional calculation methods, we use advanced numerical analysis to find elegant answers to the problems created by the interaction of ground and structure.

As part of the Tuen Mun Chek Lap Kok Link in Hong Kong, we worked on the Northern Section Tunnel. Over 4.2km in length and running to a depth of 60m beneath the sea, the tunnel accommodates three lanes of traffic at the northern entrance, requiring a world-record external diameter of 17.6m for a Tunnel Boring Machine (TBM).

Arup designed the first cellular diaphragm wall cofferdam ever constructed in Hong Kong to provide an open strut free environment which has since been adopted by others following its great success.

Trenchless tunnels

Trenchless tunnels

From traditional microtunnels to the complexities of trenchless tunnels for critical infrastructure, we provide highly-specialised services around pipe-jacking for long or curved alignments and for longer Horizontal Directional Drilling (HDD).



Image looking through London power tunnels

London Power Tunnels - the biggest upgrade to the UK's national electricity transmission system since its construction in the 1960s.

We deliver concept, detailed design and site assurance skills to de-risk microtunnels for projects from Carbon Capture & Underground Storage, hydrogen networks and windfarm cable landfalls to water and waste water infrastructure and interconnector landfalls.

Find out more about our work on the London Power Tunnels