Modular bridges: A climate-resilient solution for small bridges in the Pacific

Bridges are critical components in transport networks that significantly contribute to economic growth and social cohesion across the Pacific. If bridges are impassable, communities become isolated and economic activities grind to a halt. However, bridges are vulnerable to natural hazards and climate change, especially in Solomon Islands, an island nation in the South Pacific with annual rainfall of 3,000 to 5,000 mm per year—placing it in the top 10 countries with most precipitation. 

Add in the impacts of climate change and natural disasters, and you have the real risk of severely damaging or even destroying critical infrastructure. The Solomon Islands Ministry of Infrastructure Development (MID) faces a major challenge: it must replace deteriorating bridge infrastructure in a way that balances the costs with long-term performance. 

In 2019, an opportunity to explore innovative bridge technologies—prefabricated modular bridges (Figure 1)—arose when the Solomon Islands Roads and Aviation Project (SIRAP) was approved. One of its development goals is to strengthen the sustainability and climate resilience of roads and bridges. Grant funding from the Quality Infrastructure Investment (QII) Partnership, financed by the government of Japan, allowed a deeper look into the feasibility, design, and procurement of modular bridges under SIRAP. The project is a good example of the application of the QII Principles, by raising economic efficiency, integrating environmental and social considerations, and building resilience against natural disasters.

Why modular bridges?

Modular bridges have many potential benefits over conventional ones, most notably the shortened design and construction time.  Faster construction means road closures during construction can be shorter. It also means a reduction to safety risks to workers and disturbances to local environments. 

Modular bridges can also transform the way we deal with climate resilience. When disasters impact infrastructure, there is the opportunity to increase resilience by building back better.  Modular bridges have the potential to accelerate reconstruction after disasters by transitioning directly to permanent infrastructure rather than provisional restoration using temporary bridges.

Modular bridges also have significant social and economic benefits by expanding the number of contractors who can undertake bridge replacements. Although the concepts behind these technologies have been thoroughly tried and tested in developed countries, they are new to most developing countries.

Implementation 

The QII grant funded an assessment of prefabricated modular bridges in the Pacific. It identified 19 in-market prefabricated modular bridges and assessed their benefits and limitations in view of improving climate resilience and economic efficiency. The assessment also conducted a multi-criteria analysis through market engagement and developed a decision tree matrix to assess site-specific scenarios. 

Subsequently, a design consultant under SIRAP assessed the suitability of modular bridges for construction at the project sites in Malaita Province, one of the most populous and largest provinces of Solomon Islands. Bridge and geotechnical experts reviewed and affirmed the assessment, which determined that modular bridges were suitable for the project. Furthermore, the grant funded a workshop in the capital Honiara to disseminate the study and a plan of action supporting SIRAP.

From there, three sites were selected for bridge replacement in Malaita Province. Initially, the idea was to use a modular bridge on one site and conventional bridges for the remaining two. An open international tender was held, resulting in a single bid. The negotiations with the bidder led to the decision to construct two modular bridges. The contract between MID and Reeves Envico was signed in November 2021 and the construction of the two modular bridges is expected to be completed in 18 months. 

Lessons learned 

The study and the procurement process led to valuable lessons learned that are applicable elsewhere in the Pacific:

• Modular bridges may not always be the best solution. Local geological and hydrological conditions play a significant role in deciding whether to go modular. A site visit early on can provide better insights into conditions and limitations that could affect the decision.
• Consider the complexity of logistics. Ease of transport, the weight of components, and the level of on-site activity are important considerations for a successful bridge project.
• Avoid over-specification. Although bridge specifications must take local conditions into account, more modular bridge options with flexible specification options can be considered. 
• Talk to suppliers from the start. Engaging modular bridge suppliers early on can lead to a better procurement process, where collaboration can lead to better design. A design-and-build approach can address these constraints.

The study was pivotal in the decision making process for bridge replacement. The new modular bridges will help connect rural communities to markets, employment, and essential services such as health and education. MID is now looking at modular bridges for four other locations in Malaita Province under the recently approved Second Solomon Islands Roads and Aviation Project. Other Pacific countries facing similar challenges may also consider the approach and lessons learned here. 

Read the study: Implementation of Innovative Bridge Technologies: Technical Guidance Note.

Related posts:
Are we there yet? – A journey towards sustainable flood risk management in Pacific Island countries
Powering the Solomon Islands with reliable, affordable energy a challenge