Steps of tunnel life

• 1. Design
• 2. Construction
• 3. Commissioning
• 4. Operation

The key items to consider during each stage of the tunnel life are presented below.

1. Design

This is the most important stage of the life of a new tunnel. It is has significant influence on construction and operation costs, safety, as well as management of the technical and financial risks.

This stage requires a transverse integration of all interfaces of the “complex system" that constitutes a tunnel. This integration has to start from the earliest stage of the design.

Experience testifies to the fact that this is unfortunately rarely the case and that often the design of a tunnel results from a succession of stages considered as independent.  We note that :

• the function is not always clearly defined,
• the alignment is designed without any integration of the tunnel, of its constraints, or of the whole set of optimisation possibilities,
• the civil engineering “makes do with” the set horizontal and vertical alignments, with all the consequences that can affect the construction costs and risks,
• the equipment, safety level and operation fit in somehow and not always harmoniously or optimally with the arrangements chosen during the preliminary steps.

2. Construction

With regard to civil engineering, the most important aspect is the management of technical risks (in particular geological) and of all the resulting consequences concerning construction costs and duration.

Considerations relating to risk management for construction have to be taken into account from the design stage. These considerations must be detailed and shared with the owner of the tunnel. Decisions concerning the risks must be developed and clearly documented.

The decision to take some risks does not necessarily constitute a mistake and must not necessarily be forbidden. For example  working to a tight schedule does not allow the implementation of all the investigations that would be required to eliminate all uncertainties.

However, the decision to take a risk must result from a very detailed and soundly argued consideration of:

• consequences that may result, which must be clearly identified, analysed and consigned: delays - costs - human and environmental impacts – safety – schedule – etc.,
• the real issues of this decision, its probability of success and its real interest.

Taking  a risk must not be the result of carelessness or incompetence of the various parties.

With regard to operational facilities, the reader’s attention is drawn to:

• all aspects likely to optimise the life span of the equipment, its reliability and ease of maintenance,
• the need for a rigorous process and continuous control of the functionality, performances and quality of the equipment throughout the manufacture of the components, their assembly, their installation on the site, then at the time of partial and global testing after integration,
• the added benefit to quality concerning the choice of the equipment and the contractor, even though the construction costs may increase as a result. Possible savings due to reduced initial costs are often quickly compensated for by higher maintenance costs, difficulties of intervention under traffic, and the additional constraints that would be suffered by the users.

3. Commissioning

This stage of the "tunnel life" is often under-estimated and taken into account tardily. It requires taking time that is not often granted, and leads to the commissioning of the tunnel under unsatisfactory conditions, or even under conditions that highly expose safety risks.

This stage includes:

• the organisation of the operation and maintenance,
• development and adjusting of all operation, maintenance, intervention and safety procedures under the normal conditions of tunnel operation, as well as under MOC (Minimal Operation Conditions),
• recruitment and training of the staff that will operate the tunnel,
• the “dry run" of all the facilities, that cannot take place before the equipment has been fully completed, tested and delivered (possibly with provisions requiring only minor corrective interventions),
• the practice, training and manoeuvres involving all the intervention teams and services before commissioning the tunnel.

4. Operation

The main mission is to ensure:

• the management of all facilities, their maintenance, their repair,
• the safety and the comfort of the users.

It is also necessary to be able to step back and look objectively at daily routines in order to:

• establish feedback from experience, adapt the procedures, the intervention conditions, the training and the safety manoeuvres,
• optimise operation costs without damaging the level of service and safety,
• identify, analyse, plan and implement heavy repairs, and renovation and upgrading works.