Whether at a large or small scale, underground tunnelling is a risky business. Many of the risks are associated with the temporary works that support construction. However, with early, proactive and careful attention to some key factors, you can set up your project for success.
For safe tunnelling projects that avoid unnecessary delays or excessive pressure on project teams, it’s essential to carefully plan, scope, design and execute the temporary works. In other words, temporary works require the same level of care and professional consideration as permanent works.
Failure isn’t an option
Modern tunnelling projects run on tight schedules and financial margins, so pressures to cut time and reduce expenditure can be at the root of problems or failures. However, when comparing the cost of good practice (i.e. careful design, inspection and certification of temporary works) versus the cost of failure, the investment case is clear.
Failures of temporary works rarely stem from material failures. Problems are more commonly due to human error in the form of inadequate design, limited or no procedural control, poor construction and maintenance of the temporary works, uncontrolled modification, or using temporary works for unintended functions that were not included in the design.
When something goes wrong on a site, the consequences are likely to be far more severe and long-lasting than short-term adverse media coverage. The project proponent and contractors risk the loss of reputation, program overruns, legal proceedings, higher insurance premiums and loss of revenue. What’s far more damaging is injury to workers or members of the public.
Managing risk in the absence of standardised controls
Australia has some of the most stringent health and safety regulations in the world; however, there is no legislated procedural control for temporary works that clearly states the roles, responsibilities, design requirements, design review requirements and other aspects of temporary works. There are no recognised guidelines that describe the roles and responsibilities of clients, contractors and designers involved with developing, designing and executing temporary works. Complicating matters further, there is no harmonised health and safety regulation across all states and territories.
On large tunnelling projects, best practice tends to draw on the British standard BS5975: 2008 or internal procedures that have been based on this document. The key components of procedural controls are also well set out in international models, such as the Temporary Works Forum (TWf) UK, with its “3Ps” (people, process, product) and “4Cs” (communication, coordination, cooperation, competency). Adoption of a good practice guideline for managing and executing temporary works on construction projects would be a major step forward in Australia.
A well–written procedure that sets out rules and responsibilities for all parties involved is a key component when justifying, scoping, assessing and communicating risk to other parties. Another vital component is composing a team of individuals with the right combination of experience, qualifications and training for the complexity of the task. It is also beneficial to designate a ‘temporary works coordinator’ who acts as a single point of contact for all temporary works design and takes overall responsibility for the execution, checking, peer review and approval of temporary works design.
Consider temporary works early
It will be to the advantage of the project and all stakeholders if the client recognises the benefit of early investment in risk management. The ability to influence the execution of a design that is safe to construct is greatest in the project’s early stages. In these early stages, it is important to develop as detailed an understanding of the project’s geological and hydrogeological setting as possible. This is also the time to determine the historical and current land uses, and the existing subsurface infrastructure and services.
When you know what challenges are present, it is easier to develop the construction methodologies, sequences and scoping of temporary works that allow the construction works to get started. Addressing issues at the preliminary stages of the design is also likely to be much more cost-effective than later in the construction phase.
These early actions allow for the assessment of risks associated with temporary works, and also offer opportunities to integrate the temporary works into permanent works or, in some instances, eliminate them.
Treat temporary works as you would treat permanent works
Permanent works are often debated, developed and designed over months or years before construction, yet the development and design of temporary works are often rushed under pressure. This can lead to conservative design or mistakes.
Sufficient time and budget must be allowed for adequate temporary works design and development, and skilled, experienced professionals should be engaged to provide high-level input into developing construction methodologies and assessing risks. Engaging an experienced specialist consultant to review the risks and advise on temporary works solutions and execution during the early stages or tender phase of the project could make a huge difference throughout the life of the project, delivering a valuable return on investment.
Build better understanding and collaboration
When roles and responsibilities are not clearly outlined, parties may be unsure who is responsible for what. When permanent works are designed, the structure is considered in terms of its final form and its expected uses, loads and lifetime. However, if permanent works are designed without adequately considering the temporary works or how the structures will be built, misunderstandings or knowledge gaps can develop among the parties.
All project stakeholders must understand the importance of temporary works, and competent designers and contractors should be selected to design and construct them. However, contracts often lack detailed clauses relating to the safe design and construction of temporary works. When writing the contract, it’s advantageous to include technical personnel and encourage greater collaboration among clients, contractors, permanent and temporary works engineers.
With improved communication, better contracts and project briefs, greater use of digital models to represent the final product, and broader awareness of temporary works associated with structural design, it is far more likely that the outcome will be safe and successful.
Execute the design safely with the right support on site
It’s critical that the people on site understand the key design considerations and risks associated with temporary works and that they are constructed appropriately and conform with the designs. Unauthorised changes on site or deviations from the design can pose major risks. A helpful approach is to embed the key safety considerations, limitations and risks into the drawings and documentation for the people who are on site and doing the work.
If the temporary works on a site run into difficulties, the consequences can jeopardise the permanent works, adjacent properties, workers or the public – and can certainly affect the ultimate outcome of the project through delays and increased costs. The path to success is to treat the temporary works with the same caution and precision as the rest of the project, leaving nothing to chance.
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.
