How Engineers Manage & Control Risk During the Tunnelling Process
- SAICEL
- Dec 20, 2025
- 25 min read
Updated: Dec 20, 2025
Underground tunnelling involves working beneath the surface in challenging environments where geology, urban infrastructure, and continuous operations intersect. Safety risks are high, and managing them requires a clear, proactive approach. This post explores the key safety standards and risk frameworks that guide tunnelling projects worldwide. It also highlights training pathways available in different countries to help professionals stay current and competent
Managing risk in tunnelling requires continuous coordination between engineers, supervisors, safety representatives, and the workforce. Because tunnelling involves dynamic geology, confined spaces, heavy machinery, and multiple simultaneous hazards, the risk‑control process must be systematic, proactive, and constantly updated.
Below is a complete breakdown of how risks are managed at every stage of tunnel design and construction.
1. Planning & Pre‑Construction Risk Management
Before excavation begins, engineers and safety reps work together to identify foreseeable hazards and build a risk‑controlled design.
Key Activities
✔ Geotechnical investigations
Boreholes, lab tests, seismic surveys, groundwater analysis.
Identification of weak zones, faults, gases, inflows, settlement‑sensitive areas.
✔ Development of a Geotechnical Baseline Report (GBR)
Defines expected ground conditions and risk-sharing framework.
Provides basis for choosing the tunnelling method (TBM, SEM, drill‑and‑blast).
✔ Risk Assessment and Method Statements
Hazard identification (HAZID) sessions.
Pre‑task Risk Assessments (RAMS): Likelihood × Consequence scoring.
Safe Work Method Statements (SWMS) describing step-by-step safe execution.
✔ Safety‑by‑design
Selection of support types, segment design, waterproofing, ventilation layout, egress paths, fire systems, hyperbaric access, etc.
2. Daily / Operational Risk Management During Excavation
As excavation begins, the risk environment changes rapidly and can become quite complex. Engineers and safety representatives are tasked with continuously adapting controls and strategies to manage these evolving risks effectively. This proactive approach is essential to ensure that all workers remain safe and that the excavation process proceeds smoothly, minimizing the potential for accidents or incidents.
✔ Daily Pre‑start Meetings & Toolbox Talks
During daily pre-start meetings, teams gather to review the specific hazards of the day, which may include an assessment of ground conditions, the potential for blasting activities, and any other critical hazards such as Confined Hazardous Interactions (CHIs). This daily briefing is vital for ensuring that all team members are aware of the risks they may face and the measures in place to mitigate those risks.
In addition to reviewing hazards, these meetings serve as a platform to communicate any changes that have occurred since the last meeting, including near misses that may have taken place, newly imposed restrictions that could affect work, and the impact of weather conditions on excavation activities. This open communication fosters a culture of safety and vigilance among the workforce.
✔ Monitoring and Instrumentation
Engineers play a crucial role in managing structural and environmental monitoring throughout the excavation process. The use of advanced monitoring techniques ensures that any potential issues are identified and addressed promptly:
Ground movement sensors, including convergence meters and extensometers, are employed to detect any shifts in the earth that could indicate instability or risk of collapse. These sensors provide real-time data that is essential for maintaining site safety.
Vibration monitoring is critical, particularly in areas where blasting or Tunnel Boring Machines (TBMs) are in operation. This monitoring helps to assess the impact of vibrations on surrounding structures and the excavation site itself, ensuring that any excessive vibrations are mitigated.
Gas monitoring systems are installed to detect hazardous gases such as methane (CH₄), hydrogen sulfide (H₂S), carbon monoxide (CO), and oxygen (O₂) levels. Continuous monitoring of these gases is vital for the safety of workers, particularly in confined spaces where gas accumulation can pose serious risks.
Ventilation flow and air-quality monitoring are implemented to ensure that the air within the excavation site remains safe to breathe. Adequate ventilation is crucial in preventing the buildup of harmful gases and maintaining a healthy working environment.
Monitoring face pressure, slurry density, and other operational parameters of TBMs is also essential. These metrics help engineers ensure that the machinery operates within safe limits and that the excavation process remains stable and efficient.
✔ Worker Safety Checks
To further enhance safety measures, safety representatives conduct thorough checks to verify compliance with safety protocols:
Ensuring that all personnel are wearing appropriate Personal Protective Equipment (PPE) is a fundamental aspect of safety checks. This includes hard hats, gloves, goggles, and other necessary gear tailored to the specific hazards present on-site.
Safety reps also assess access and egress routes to confirm that they are clear and well-marked, allowing workers to evacuate quickly in case of an emergency. These routes must be regularly inspected and maintained to ensure their effectiveness.
Emergency equipment readiness is another critical focus area. Safety representatives check that all emergency equipment, such as first aid kits, fire extinguishers, and rescue gear, is easily accessible and in proper working order, ready to be deployed if needed.
Verification of confined space permits is essential for any work taking place in enclosed areas. These permits ensure that all safety protocols are followed, including atmospheric testing and proper ventilation, to protect workers from potential hazards.
Finally, hot-work permits must be checked to ensure that any activities involving open flames or sparks are conducted safely, with appropriate precautions in place to prevent fires or explosions.
3. Engineering Controls (Primary Risk Controls)
Engineering controls represent the most effective and robust level of risk mitigation strategies implemented within the tunnel environment. These controls are designed to systematically minimize hazards by altering the physical environment rather than relying solely on worker behavior or administrative policies. By integrating these controls into the design and operation of tunnel projects, safety is inherently prioritized, ensuring that the risks associated with tunneling activities are significantly reduced.
✔ Ground Support & Stability Controls
To maintain structural integrity and ensure the safety of personnel, various ground support techniques are employed. These include the installation of rock bolts, which are anchored into the rock to provide additional stability. Ribs, which are structural supports placed at intervals, help to maintain the tunnel shape. Additionally, the use of sprayed concrete lining (SCL) or shotcrete provides a protective layer that reinforces the tunnel walls. Mesh is often utilized to prevent smaller debris from falling, while steel sets serve as a robust framework that supports the tunnel structure during excavation and beyond.
Moreover, a real-time review system for ground classification and support class changes is crucial. This system allows for immediate assessment and adaptation to changing geological conditions, ensuring that the appropriate level of support is maintained throughout the tunneling process. Continuous monitoring and assessment help in making informed decisions that can prevent potential collapses and enhance overall safety.
✔ Ventilation & Atmospheric Controls
Effective ventilation systems are essential in tunnel environments, particularly to ensure that fresh air is continuously supplied to the working face. A forced ventilation system is typically employed to circulate air, thereby preventing the build-up of harmful gases and ensuring that workers have access to breathable air. This system is crucial not only for comfort but also for the health and safety of all personnel involved in tunneling operations.
In addition to providing fresh air, exhaust extraction systems are implemented to remove dust, diesel emissions, and other airborne contaminants. This is vital for maintaining air quality and protecting the respiratory health of workers. Such systems must be regularly maintained and monitored to ensure their effectiveness.
Automatic alarms are integrated into the ventilation system to alert workers in the event of gas exceedance, ensuring that any dangerous accumulation of gases such as methane or carbon monoxide is promptly detected and addressed. These alarms are a critical component of safety protocols, allowing for immediate evacuation or remediation measures to be taken.
✔ Water & Pressure Management
Water ingress can pose a significant risk in tunneling operations, making effective water management strategies essential. Pre-grouting techniques are often employed to seal the ground and prevent water from entering the tunnel. In cases of severe water infiltration, ground freezing may be necessary to create a temporary barrier, ensuring that excavation can proceed safely.
High-capacity sump pumps are installed to manage any water that does enter the tunnel. These pumps are equipped with backup power systems to ensure functionality even in the event of a power failure, thus preventing flooding and maintaining a safe working environment. Regular inspections and maintenance of these pumps are essential to ensure their reliability.
Additionally, tunnel boring machine (TBM) chamber pressure regulation systems are implemented to control and prevent inflows of water. By maintaining appropriate pressure levels within the chamber, the risk of sudden water inflow is significantly reduced, enhancing the safety of the tunneling operation.
✔ Machinery Controls
To safeguard workers from machinery-related hazards, various control measures are put in place. This includes the installation of guarding on conveyors and other moving parts to prevent accidental contact. Lockout/tagout (LOTO) procedures are strictly enforced to ensure that machinery is properly shut down and cannot be accidentally restarted during maintenance or inspection activities.
Furthermore, speed limits for vehicles operating underground are established to reduce the risk of accidents. These limits are enforced through signage and monitoring systems to ensure compliance by all operators.
Segregation barriers are strategically placed to create safe zones between machinery and pedestrian pathways. This physical separation minimizes the risk of collisions and ensures that workers can navigate the site safely without exposure to moving equipment.
In summary, the implementation of engineering controls is critical in creating a safe and efficient tunneling environment. By focusing on ground support, ventilation, water management, and machinery controls, these measures collectively contribute to the overall risk mitigation strategy, safeguarding the health and safety of all personnel involved in tunneling operations.
4. Administrative Controls (Operational Risk Controls)
Safety representatives play a crucial role in ensuring that safe systems of work are not only enforced but also regularly updated to reflect the latest safety standards, practices, and regulations. Their responsibilities encompass a wide range of activities aimed at minimizing operational risks and fostering a culture of safety within the workplace. This includes the development, implementation, and continuous improvement of operational risk controls that are essential for maintaining a safe working environment.
✔ Permit‑to‑Work Systems
Confined space entry: This involves strict protocols that must be followed when workers enter spaces that are not designed for continuous occupancy, such as tanks, silos, or pipelines. Safety representatives ensure that risk assessments are conducted, appropriate ventilation measures are in place, and that all personnel are equipped with the necessary safety gear and training to mitigate the risks associated with such environments.
Electrical isolation: This system is vital for ensuring that all electrical equipment is properly de-energized before maintenance or repair work begins. Safety representatives oversee the implementation of lockout/tagout procedures to prevent accidental re-energization, thereby protecting workers from electrical hazards.
Hyperbaric entry: In operations involving hyperbaric conditions, such as underwater welding or repairs, safety representatives ensure that protocols are established for safe entry and exit from hyperbaric chambers. This includes monitoring pressure levels and ensuring that all personnel are trained in the specific risks associated with hyperbaric environments.
Hot‑work permits: These permits are essential for any work that involves open flames or the generation of sparks, such as welding or cutting. Safety representatives ensure that proper precautions are taken, including fire watch protocols and the identification of potential ignition sources nearby.
Lifting operations: Safety representatives are responsible for overseeing lifting operations, ensuring that all lifting equipment is inspected and certified, and that personnel are trained in safe lifting practices. This includes the use of cranes, hoists, and other lifting devices, as well as the importance of load stability and weight limits.
✔ Training & Competency
Tunnelling inductions, emergency drills, gas monitoring, TBM operator certification: Comprehensive training programs are essential for all workers involved in tunnelling operations. Safety representatives ensure that personnel are adequately trained in the specific hazards associated with tunnelling, including the use of gas monitoring equipment and emergency response procedures. Certification for Tunnel Boring Machine (TBM) operators is also a critical component of this training to ensure competency in operating complex machinery safely.
Specialist training for hyperbaric operations and blasting: Specialized training programs are developed for workers involved in hyperbaric operations and explosive handling. This training covers the unique risks associated with these activities, including the safe handling of materials, understanding of pressure dynamics in hyperbaric environments, and the implementation of strict safety protocols to prevent accidents.
✔ Shift Management & Fatigue Control
Ensuring adequate rest periods: Safety representatives monitor work schedules to ensure that all employees receive adequate rest periods to prevent fatigue-related incidents. This includes implementing policies that limit consecutive working hours and promote regular breaks, which are essential for maintaining alertness and performance on the job.
Monitoring for heat stress and overexertion: In environments where workers are exposed to extreme temperatures or physically demanding tasks, safety representatives are tasked with monitoring conditions that could lead to heat stress or overexertion. This includes providing hydration stations, scheduling work during cooler parts of the day, and training workers to recognize the signs of heat-related illnesses.
✔ Communication Systems
Leaky-feeder radio communication: This system is crucial for maintaining communication in areas where traditional radio signals may be weak or obstructed, such as underground tunnels. Safety representatives ensure that the leaky-feeder system is properly installed and maintained, allowing for continuous communication among workers and supervisors to enhance safety and response times during emergencies.
Check-in/check-out worker tracking: Implementing a check-in/check-out system helps track the location and safety of workers, especially in hazardous environments. Safety representatives oversee the deployment of this system to ensure that all personnel are accounted for at all times, facilitating quick responses in case of emergencies.
Emergency muster procedures: Safety representatives develop and regularly drill emergency muster procedures to ensure that all workers know where to go and what to do in the event of an emergency. These procedures are critical for ensuring that personnel can be quickly and safely evacuated from dangerous situations.
Through these comprehensive administrative controls, safety representatives not only enhance the overall safety culture within the organization but also significantly reduce the likelihood of accidents and incidents in the workplace. Their proactive approach to risk management is essential for ensuring that all employees can perform their duties in a safe and secure environment.
5. TBM‑Specific Risk Management
TBM (Tunnel Boring Machine) operations require additional layers of monitoring and control due to the complex and often hazardous environments in which they operate. The unique challenges presented by underground construction necessitate a rigorous approach to risk management, ensuring the safety of personnel and the integrity of the project.
✔ Face Pressure Control
Engineers closely monitor a variety of critical parameters to maintain safe operational conditions at the face of the tunnel. These parameters include:
Chamber pressure: Continuous measurement of the pressure within the TBM's chamber is essential to prevent any sudden changes that could lead to structural failures or hazardous conditions.
Screw conveyor load: Monitoring the load on the screw conveyor helps ensure that the material being transported is within safe limits, preventing overloading that could cause mechanical failures.
Slurry density: The density of the slurry must be carefully maintained to ensure proper support of the tunnel face and to avoid issues such as excessive ground movement or hydraulic imbalance.
Torque & advance rate: Tracking the torque exerted by the TBM and its rate of advance is crucial for detecting any irregularities that could indicate potential problems, such as increased resistance from geological formations.
This comprehensive monitoring system is vital to prevent catastrophic events such as tunnel collapse, blowouts, and uncontrolled inflows of water or soil, all of which pose significant risks to both the machinery and the workforce involved in the operation.
✔ Hyperbaric Safety
In the context of TBM operations, hyperbaric safety is of paramount importance, particularly when working in environments with elevated pressure conditions. Safety representatives ensure the following measures are in place:
Medical clearance: All personnel must undergo thorough medical evaluations to ensure they are fit to work in high-pressure environments, minimizing the risk of health complications.
Decompression tables: Detailed decompression tables are maintained and regularly updated, providing essential guidelines for safely returning personnel to surface pressure after exposure to high-pressure conditions.
Gas quality control: Continuous monitoring of the air quality within the working environment is critical to ensure that it remains safe for breathing and free from harmful contaminants.
DCS (Decompression Sickness) emergency response: A well-defined and practiced emergency response plan for dealing with decompression sickness is essential, ensuring that immediate medical assistance is available if needed.
✔ Backup Gantry Safety
Maintaining a safe working environment around the backup gantry is crucial for the protection of the crew and the efficient operation of the TBM. Key safety measures include:
Clear walkways: Ensuring that all walkways are kept clear of obstacles promotes safe movement throughout the site, reducing the risk of trips and falls.
Housekeeping: Regular housekeeping practices help maintain a clean and organized work environment, which is essential for safety and efficiency.
Handrails: The installation of sturdy handrails along walkways and elevated areas provides additional support and safety for workers navigating the site.
Lighting: Adequate lighting is essential to ensure visibility in all areas of the site, particularly in darker sections, which can pose hazards.
Safe cable management: Proper management of cables and other equipment is critical to prevent entanglement and trips, thereby enhancing overall safety on the job site.
6. Emergency Preparedness & Response
Engineers and safety teams must be thoroughly prepared for unexpected events that could arise during TBM operations. This involves developing comprehensive emergency preparedness and response strategies to effectively manage potential crises.
✔ Refuge Chambers
Refuge chambers serve as critical safe havens for personnel in the event of an emergency. These chambers are:
Fully equipped: Each chamber is stocked with breathable air supplies, communication devices, emergency lighting, and medical kits, ensuring that workers have access to essential resources during an emergency situation.
✔ Fire & Smoke Response
Fire safety is a top priority in TBM operations, where the risk of fire and smoke can be heightened due to machinery and materials involved. To mitigate these risks, the following measures are implemented:
Fire suppression equipment: Fire suppression systems are strategically installed at regular intervals throughout the worksite to quickly address any fire outbreaks that may occur.
Procedures for ventilation reversal: Established procedures for reversing ventilation systems are critical in the event of smoke detection, allowing for the safe removal of smoke and toxic gases from the area.
✔ Evacuation Plans
Effective evacuation plans are essential for ensuring the safety of all personnel in emergency situations. These plans include:
Simulation drills: Regular simulation drills are conducted under conditions that mimic smoke and blackout scenarios, allowing team members to practice their responses and improve their readiness for real emergencies.
Multi-discipline coordination: Coordination between various disciplines, including the fire brigade and rescue teams, is crucial for a unified response to emergencies, ensuring that all teams work together seamlessly to safeguard personnel and manage the situation effectively.
7. Continuous Improvement & Review
Risk control is a dynamic and ongoing process that requires constant vigilance, adaptation, and enhancement to ensure safety and efficiency in operations. It is essential to recognize that as conditions change and new information becomes available, so too must our strategies for managing risks. This continuous improvement mindset is fundamental to fostering a culture of safety and operational excellence.
✔ Incident & Near‑Miss Reporting
Safety representatives play a crucial role in the risk management framework by systematically gathering data related to incidents and near-misses. This reporting process is not merely a formality; it serves as a vital feedback loop that informs decision-making and process enhancements. By analyzing the circumstances surrounding each incident, safety reps can identify patterns, root causes, and potential areas for improvement. The information collected is then utilized to refine existing safety protocols, develop targeted training programs, and implement proactive measures designed to prevent similar occurrences in the future. This comprehensive approach not only improves safety outcomes but also promotes a culture where employees feel empowered to report hazards without fear of repercussions.
✔ Daily Review of Ground Conditions
Engineers conduct daily reviews of ground conditions to ensure that all operational parameters are suited to the current environment. This regular assessment is critical, especially in dynamic settings such as construction sites or underground tunneling projects where geological conditions can change rapidly. By closely monitoring these conditions, engineers can make informed decisions regarding the modification of support classes or Tunnel Boring Machine (TBM) parameters. Such adjustments are essential to maintaining structural integrity and ensuring the safety of personnel working in potentially hazardous environments. These daily reviews not only mitigate risks but also enhance overall project efficiency by allowing for timely interventions that can prevent costly delays or accidents.
✔ Ongoing Safety Audits
Conducting ongoing safety audits is a fundamental component of maintaining compliance with established safety standards and regulatory requirements. These audits serve as a systematic evaluation of the effectiveness of safety management systems and practices. By regularly assessing compliance, organizations can identify gaps in their safety protocols and take corrective actions before issues escalate. The audit process often involves comprehensive checks of equipment, procedures, and employee adherence to safety guidelines. Furthermore, the findings from these audits can provide valuable insights that inform training needs and policy adjustments, ensuring that safety remains a top priority throughout the organization. Continuous auditing fosters an environment of accountability and transparency, reinforcing the commitment to maintaining high safety standards.
✔ Updating the Risk Register
The risk register is a living document that must be regularly updated to reflect new hazards and the corresponding controls put in place to mitigate them. As projects evolve and new risks emerge, it is imperative to document these changes meticulously. This process involves not only the identification of new risks but also the assessment of their potential impact and likelihood. By updating the risk register, organizations can ensure that all stakeholders are aware of current risks and the measures in place to address them. This proactive approach promotes a culture of safety and preparedness, as it encourages ongoing dialogue about risk management among team members. Additionally, having an up-to-date risk register facilitates better decision-making and resource allocation, ultimately leading to safer and more efficient operations.
Why a Global Safety Mindset Matters in Tunnelling
Tunnelling projects face unique hazards such as ground collapse, gas leaks, fire, and equipment failure. These risks demand a safety-by-design approach where safety is integrated from planning through construction and operation. Many leading projects adopt risk-based management to identify, assess, and control hazards systematically.
International organizations like the International Tunnelling Association (ITA-AITES) play a vital role by developing global guidelines and facilitating knowledge exchange. Their work helps align safety practices across countries, ensuring that lessons learned in one region benefit projects worldwide.
Key Safety Standards Around the World
Different countries have developed detailed safety standards tailored to their regulatory environments and tunnelling challenges. Here are some of the most important:
United Kingdom — BS 6164:2019 Health & Safety in Tunnelling
This comprehensive code covers all aspects of tunnelling safety including ground investigation, sprayed concrete lining (SCL) safety, fire and smoke control, ventilation, compressed air work, and instrumentation monitoring. It provides practical guidance for contractors and engineers.
United States — OSHA Underground Construction (Tunneling)
OSHA’s standard outlines requirements for ground support, air quality monitoring, ventilation, lighting, fire prevention, hoisting operations, emergency procedures, and compressed air work. It emphasizes worker protection and emergency readiness.
European Union — Directive 2004/54/EC for Road Tunnels 500 meters or longer
This directive sets minimum safety requirements for road tunnels, focusing on fire safety, ventilation, emergency exits, and communication systems. It harmonizes safety across member states to protect tunnel users and workers.
These standards provide a foundation for safe tunnelling but often require adaptation to local conditions and project specifics.
Understanding Risk Frameworks in Tunnelling Projects
Risk frameworks are essential tools that guide project teams in the complex environment of tunnelling projects. These frameworks facilitate the identification of potential hazards, the evaluation of associated risks, and the implementation of effective control measures to mitigate those risks. The structured approach inherent in risk frameworks ensures that all aspects of a tunnelling project are carefully considered, allowing for a safer and more efficient operational environment. Common elements that form the backbone of these frameworks include:
Hazard Identification
This process involves a systematic and thorough review of various factors that could pose risks, including geological conditions, the functionality and safety of equipment, and the work processes employed by the team. By conducting detailed assessments of the surrounding environment and operational practices, teams can pinpoint potential dangers that may arise during the tunnelling process. This could include identifying unstable geological formations, assessing the integrity of machinery, and evaluating the safety of work methods to ensure that all possible hazards are recognized before work begins.
Risk Assessment
Once hazards have been identified, the next step is to assess the risks associated with these hazards. This involves estimating both the likelihood of a hazard occurring and the potential impact it could have on the project, workers, and the surrounding environment. Risk assessment can be conducted using qualitative methods, which rely on subjective judgment and experience, or quantitative methods, which use statistical data and mathematical models. By employing these techniques, project teams can prioritize risks and allocate resources effectively to manage them, ensuring that the most significant threats are addressed promptly.
Control Measures
After risks have been assessed, the next critical phase involves implementing control measures designed to mitigate those risks. These measures can include a range of strategies, such as engineering controls that physically alter the work environment to reduce hazards, administrative procedures that define safe work practices, and the use of personal protective equipment (PPE) to safeguard workers. Effective control measures are vital for creating a safe working environment and must be tailored to the specific risks identified in the assessment phase.
Monitoring and Review
Risk management is not a one-time activity; it requires ongoing monitoring and review to ensure that control measures remain effective and relevant. Continuous observation of risk controls allows project teams to identify any changes in conditions that may necessitate updates to risk assessments or the implementation of new control measures. By maintaining a proactive approach to risk management, teams can adapt to evolving circumstances and ensure that safety remains a top priority throughout the duration of the tunnelling project.
For example, the UK’s BS 6164 standard integrates risk management with safety design principles, mandating that documented risk assessments be performed at every stage of the tunnelling process. This ensures that safety considerations are embedded in the project from the outset. In the United States, OSHA (Occupational Safety and Health Administration) mandates regular inspections and air quality monitoring to detect hazards early, thereby fostering a culture of safety that prioritizes the well-being of workers and the integrity of the project.
Training Pathways by Country
Competent personnel are indispensable for maintaining safety and efficiency in tunnelling operations. Training programs designed to equip workers with the necessary skills and knowledge vary significantly by country, reflecting local regulations, industry standards, and specific project requirements. However, these programs generally encompass several key areas of focus:
Technical Skills
Training in technical skills is crucial for ensuring that personnel are well-prepared to handle the complexities of tunnelling work. This includes comprehensive instruction on ground investigation techniques to assess soil and rock conditions, support installation methods to ensure structural integrity, ventilation management to maintain air quality within the tunnel, and emergency response protocols to effectively address any incidents that may arise. By equipping workers with these essential skills, training programs help to foster a knowledgeable workforce capable of executing tunnelling projects safely and efficiently.
Safety Awareness
Safety awareness training is a critical component of any tunnelling program, as it helps workers understand the various hazards they may encounter on the job. This training covers safe work practices, the proper use of protective equipment, and strategies for recognizing and responding to potential dangers. By instilling a strong safety culture among workers, organizations can significantly reduce the likelihood of accidents and injuries on the job site, ultimately leading to a more productive and secure working environment.
Regulatory Compliance
Familiarity with national standards and regulatory requirements is vital for ensuring that tunnelling projects comply with legal obligations and industry best practices. Training programs typically include instruction on relevant regulations, reporting requirements, and safety standards that govern tunnelling operations in a specific country. By ensuring that personnel are well-versed in these regulations, organizations can minimize the risk of non-compliance, which can lead to significant legal and financial repercussions, as well as jeopardizing the safety of workers and the success of the project.
Here are examples of training pathways:
UK: The National Specialist Contractors Council offers accredited courses aligned with BS 6164. Many contractors require certification in confined space entry and compressed air work.
USA: OSHA provides training materials and certification programs for underground construction safety. The National Institute for Occupational Safety and Health (NIOSH) also offers research-based training.
Europe: Various EU countries provide training based on Directive 2004/54/EC, often through vocational schools and industry associations.
Investing in ongoing training ensures workers and supervisors stay updated on best practices and regulatory changes.
Practical Examples of Safety Implementation
A tunnelling project in London used BS 6164 guidelines to design a ventilation system that maintained air quality despite complex underground conditions. Continuous monitoring allowed early detection of hazardous gases, preventing incidents.
In New York, OSHA standards guided emergency drills and hoisting safety protocols during subway expansion. These measures reduced accidents and improved worker confidence.
A highway tunnel in Germany followed EU directives to install fire-resistant materials and emergency exits every 250 meters, enhancing evacuation safety.
These examples show how standards and risk frameworks translate into real-world safety improvements.
Safety in underground tunnelling requires clear standards, effective risk management, and skilled personnel. By following established guidelines like BS 6164, OSHA regulations, and EU directives, projects can reduce hazards and protect workers. Training programs tailored to local regulations help maintain a competent workforce ready to face tunnelling challenges.
For professionals involved in tunnelling, staying informed about global safety practices and investing in continuous training are key steps toward safer projects. Explore the linked standards and training resources to build your knowledge and contribute to safer underground construction.
Tunnelling Risk Matrix, Control Measures & TBM Safety Protocols
Hazard | Description | Likelihood (1–5) | Consequence (1–5) | Risk Rating |
Ground Collapse / Rock Fall | Weak geology, fault zones, inadequate ground support leading to sudden roof or wall failure. | 4 | 5 | 20 – Extreme |
Water Ingress / Flooding | Sudden inflow from aquifers, fractured zones, or impounded water causing rapid flooding. | 3 | 5 | 15 – High |
Toxic / Flammable Gases | Methane, hydrogen sulphide, carbon monoxide; risk of explosion or asphyxiation. | 4 | 5 | 20 – Extreme |
Poor Ventilation / O₂ Deficiency | Insufficient airflow, build‑up of fumes or dust, or displacement of oxygen by gases. | 4 | 4 | 16 – High |
Fire & Explosion | Fires from overheating equipment, electrical faults, fuel storage, or gas pockets. | 3 | 5 | 15 – High |
Blasting Hazards | Misfires, flyrock, overbreak, high vibration transmission, shockwaves. | 3 | 4 | 12 – High |
TBM Cutterhead / Hyperbaric Hazards | Pressurised interventions, cutterhead blockages, decompression injuries. | 3 | 5 | 15 – High |
Machinery Strikes | Mobile plant (locos, loaders, trucks) striking workers in confined spaces. | 4 | 4 | 16 – High |
Dust & Fumes | Silica dust, diesel exhaust, noxious fumes producing health hazards. | 5 | 3 | 15 – High |
Heat Stress | Heavy labour in a hot, humid, poorly ventilated tunnel environment. | 4 | 3 | 12 – High |
Limited Egress | Restricted escape routes, narrow passageways, congestion during emergencies. | 3 | 4 | 12 – High |
How to Calculate a Risk Rating (Simple & Industry‑Standard Method)
Risk rating in tunnelling is calculated using the classic Likelihood × Consequence formula.
Risk Rating = Likelihood (L) × Consequence (C)This is the method used in construction, tunnelling, OSHA frameworks, and most engineering risk assessments.
1. Define the Two Components
A. Likelihood (L)
How probable is it that the hazard will occur?
Typical tunnelling scale (1–5):
Score | Likelihood | Meaning |
1 | Rare | May occur only in exceptional circumstances |
2 | Unlikely | Could occur, but very rarely |
3 | Possible | Might occur at some time |
4 | Likely | Expected to occur in many situations |
5 | Almost Certain | Occurs frequently or repeatedly |
B. Consequence (C)
How severe is the harm if it happens?
Typical consequence scale (1–5):
Score | Severity | Meaning |
1 | Minor | First‑aid injury, no disruption |
2 | Moderate | Medical treatment, minor damage |
3 | Serious | Lost time injury, moderate damage |
4 | Major | Major injuries, significant damage |
5 | Catastrophic | Fatalities, major failure, collapse |
2. Apply the Formula
Once the L and C values are decided, multiply them:
Risk Rating = L × C
Example:A methane gas pocket in a tunnel = Likelihood 4 (Likely) and Consequence 5 (Catastrophic)
Risk Rating = 4 × 5 = 20 (Extreme Risk)
3. Interpret the Risk Rating
Example risk rating scale:
Risk Score | Category | Required Action |
1–5 | Low | Acceptable with routine monitoring |
6–10 | Medium | Manage with controls; monitor regularly |
11–15 | High | Must implement strong controls; senior sign‑off |
16–25 | Extreme | Stop work until risk is reduced; redesign or engineer out hazard |
4. Example Calculation (From Your Matrix)
Hazard: Heat Stress in Tunnelling
Likelihood = 4 (Likely)
Consequence = 3 (Serious)
Risk Rating = 4 × 3 = 12 → High Risk
Meaning: controls such as cooling ventilation, hydration, and work‑rest cycles must be implemented before continuing work.
5. Why Multiplication Is Used
Multiplying the values gives:
A quantitative score (so hazards can be ranked)
A consistent framework across all disciplines
A transparent approach for audits, clients, and regulators
It is used widely in tunnelling risk frameworks, including in risk guidelines such as those applied in underground construction safety. [mdpi.com]
6. Optional: Enhanced Methods
Major infrastructure projects may add:
✔ Residual risk score (after controls)✔ ALARP assessment (As Low As Reasonably Practicable)✔ Bow‑tie analysis✔ Risk matrices per discipline (geotechnical, mechanical, fire, environment)
If you'd like, I can build your project‑specific risk register, including:
Automatic risk scoring
Pre‑defined tunnelling hazards
TBM-specific risks
Control hierarchy (Eliminate, Substitute, Engineer, Admin, PPE)
CONTROL MEASURES FOR EACH MAJOR RISK
A. Geotechnical Risks
Hazards: Collapse, rock fall, unstable ground. Controls:
Detailed geotechnical investigation including boreholes, seismic surveys.
Immediate installation of primary support (SCL/shotcrete, rock bolts, mesh).
Define exclusion zones around unsupported faces.
Use instrumentation: convergence monitoring, extensometers, inclinometers.
Regular review of the Geotechnical Baseline Report (GBR).
B. Water Ingress / Flooding
Controls:
Pre-excavation grouting (cementitious or chemical).
Probe drilling ahead of excavation.
Stand‑by emergency pumps with backup power.
Water-tight tunnel linings and gasketed segments.
Flood-control emergency procedure.
C. Gas Hazards (Flammable or Toxic)
Controls:
Continuous gas monitoring (CH₄, H₂S, CO, O₂).
Explosion-proof electrical equipment.
Ventilation with alarms and automatic shutdown.
Permit-to-work for hot works.
Emergency evacuation plan for gas exceedance.
D. Ventilation Issues / Oxygen Deficiency
Controls:
Primary and secondary ventilation systems.
Diesel particulate filtration.
Portable auxiliary fans for dead-end headings.
Air‑quality monitoring at worker breathing height.
E. Fire & Explosion
Controls:
Fire-resistant cabling and fire-rated enclosures.
Strict separation zones for fuel storage.
Automatic fire suppression where applicable.
Hot‑work permits and isolation controls.
Regular fire drills inside the tunnel.
F. Blasting Hazards
Controls:
Certified shotfirers only.
Misfire identification and clearance protocols.
Blast mats and protective screens where needed.
Air overpressure and vibration monitoring.
Blasting schedules coordinated with site closures.
G. Machinery Strikes / Crushing
Controls:
One-way traffic routes underground.
Designated pedestrian walkways.
Proximity alarms on vehicles.
Banksmen (spotters) for vehicle movements.
Mandatory visibility PPE (hi‑vis, helmet lights).
H. Dust, Silica, Diesel Fumes, Noise
Controls:
Water sprays, foam suppression, mist cannons.
Exhaust scrubbers on diesel machinery.
Regular air sampling for silica and particulates.
Hearing protection and sound barriers.
I. Heat Stress
Controls:
Ventilation upgrades with cooling air.
Hydration stations inside tunnel.
Job rotation to reduce continuous exposure.
Heat-stress monitoring (WBGT).
J. Egress Constraints
Controls:
Refuge chambers spaced according to regulations.
Emergency signage and illuminated escape paths.
Redundant escape routes where possible.
Emergency drills including smoke simulations.
TBM-SPECIFIC SAFETY PROTOCOLS (Greatly Expanded)
A. TBM Operation & Excavation Face Stability
Maintain correct EPB or slurry chamber pressure to balance ground.
Continuous monitoring of cutterhead torque, penetration rate, advance rate.
Soil conditioning (foam, polymer, bentonite) for smoother excavation.
Avoid over-excavation and control volume loss to limit settlement.
Automated monitoring for screw conveyor pressure and load.
B. Hyperbaric Interventions (CHI)
Required when the cutterhead chamber must be accessed under pressure.
Protocols:
Workers must undergo hyperbaric medical examination.
Compression/decompression procedures must follow approved decompression tables.
Hyperbaric chamber gas monitoring: O₂, CO₂, humidity, temperature.
Strict control of bottom time and exposure limits.
Emergency DCS (Decompression Sickness) response plan with medical support.
C. Mechanical / Electrical Safety
Lock-out / Tag-out (LOTO) before servicing rotating machinery.
All TBM moving parts must have interlocked guards.
Emergency stop buttons along TBM length and backup gantries.
Overload protection for electrical equipment.
Vibration and structural monitoring of TBM shield and backup.
D. Ventilation & Gas Management for TBM Operations
Forced ventilation ducting delivering fresh air to the cutterhead.
CH₄ and O₂ real-time monitoring displayed in TBM cabin.
Auxiliary fans during maintenance stops.
Ventilation redundancy with backup power.
E. Slurry / Muck Handling Safety
Pressure-balanced slurry pipelines to prevent blowouts.
Confined space permit for slurry tank entry and cleaning.
Guarding on conveyors and transfer points.
Fall prevention around slurry separation plant walkways.
F. TBM Backup System Safety
Clear walkways on backup gantries with anti-slip surfacing.
Proper cable and hose management to avoid trip hazards.
Adequate lighting, handrails, and signage.
Regular housekeeping to prevent material accumulation.
G. TBM Emergency Management
Refuge chambers located at appropriate intervals.
Emergency evacuation drills covering power loss scenarios.
Rescue plan for TBM entrapment or main bearing failure.
Tracking of all personnel (check-in / check-out) at TBM entry points.
Conclusion
Tunnelling remains one of the most intricate and high-risk endeavors in modern infrastructure development, where success hinges on a thorough understanding of geological behavior, mechanical systems, atmospheric hazards, and human performance. By employing structured risk assessment methods, like the Likelihood × Consequence matrix, project teams can objectively identify, prioritize, and mitigate the most critical threats from ground collapse and water ingress to toxic gases, fire, limited egress, and TBM-specific hazards. These tools assist in transforming uncertainty into manageable, measurable risk, enabling safer decision-making throughout the design and construction lifecycle.
Equally critical are the control measures that turn analysis into action: robust geotechnical investigation, engineered ground support, advanced ventilation and monitoring systems, strict traffic and equipment protocols, hyperbaric safety practices, and comprehensive emergency planning. When applied consistently and backed by competent training, these measures significantly decrease the likelihood of serious incidents underground.
Finally, the specialized nature of TBM operations requires an additional layer of disciplined safety protocols. Face pressure control, soil conditioning, hyperbaric CHI management, machinery isolation, and slurry system safety all work together to maintain stability at the excavation front and protect the crew from potentially life-threatening conditions.
Ultimately, world-class tunnelling safety is achieved when engineering excellence, risk-based thinking, and operational discipline collaborate. By combining rigorous planning, continuous monitoring, and a proactive safety culture, tunnelling teams can deliver projects efficiently, sustainably, and most importantly, safely. This integrated approach not only protects workers but also strengthens public confidence in the underground infrastructure that shapes our cities and connects our communities.
Engineers and safety representatives manage tunnelling risks through a layered system of engineering controls, monitoring, communication, training, and emergency readiness. Effective tunnelling safety depends on:
Anticipating hazards before excavation
Controlling risks through engineered systems
Actively monitoring changing conditions
Empowering safety reps to intervene at any time
Strong teamwork between engineering, operations, and H&S
With this integrated approach, tunnelling becomes safer, more predictable, and more efficient even in the most complex ground conditions.
Comments