This case study, focusing on an urban development in Malaysia, shows the material’s potential as a lightweight structural component improving a key asset’s resilience to flooding.
Malaysia’s capital, Kuala Lumpur (KL), lies at the point where the Klang River merges with its tributary, the Gombak.
These watercourses have become narrower as the city – the name of which translates as “muddy estuary” – has developed since the mid-19th century.
The risk of fluvial (river) flooding in a city facing two monsoon seasons a year is therefore high.
This is despite protective measures such as the construction of river embankments.
After a prolonged spell of heavy rain at the end of April 2022, for instance, several areas around KL were flooded.
Riveria City is a residential and commercial development in KL adjoining the Klang River.
From the early stages of its construction in 2018, its transport links were marketed as a strong selling point.
One of these was an access road that would bridge the river and join Federal Route 2, a major highway connecting the capital to other key cities.
The proposed new bridge over the Klang would feature an entry and exit ramp structure on the Riveria City side tying into the development’s existing riverside road.
This road had been built on an elevated deck spanning between a piled river wall and columns on piled foundations in 2014.
The redesign challenge
Concerned about the safety and functionality of the planned bridge during flooding, Malaysia’s Department of Irrigation and Drainage called for it be raised by 40cm.
This design modification would provide enough freeboard (clearance below the bridge’s underside, or soffit) for a so-called Q100 flood event on the Klang.
This type of event is where the water level is deemed to have a 1% chance of occurring in any one year.
While this requirement could be accommodated relatively easily on the highway side of the river, it posed more of a challenge on the Riveria City side. This was because the new design would lift the bridge’s ramps significantly higher than the riverside road.
Simply adding a 40cm layer of conventional fill to the deck supporting the road seemed the most obvious way to equalise their heights.
But a structural assessment found that it wouldn’t be able to bear the extra gravity load imposed by the amount of material this would need.
It looked like the next best solution would be to demolish the structure and build a new one at the required level.
Doing that would not only be time-consuming but also have a significant environmental impact, so it was hardly ideal.
An innovative solution
Design consultancy HSS Engineers proposed adding a layer of expanded polystyrene (EPS) as a lightweight fill material on top of the central section of the 90m by 6.9m deck.
This approach would not only eliminate the need for a new structure to be built but also offer environmental benefits and cost savings.
The contractor, Dura, removed the deck’s surface layer over an area measuring 30.2m by 6.9m. It then installed EPS in layers to total depths ranging from 5cm up to 40cm to achieve the desired profile.
Dura covered the EPS with polyethylene sheeting and topped this with a 5cm layer of ultra-high-performance concrete, which was then resurfaced to provide smooth joins to the surfaces connected to the raised section.
Using EPS as a fill material reduced the project’s carbon impact by 83% compared with the demolition and reconstruction option – an estimated emission saving of 43.9t of CO2e.
The cost saving achieved was about £107,000.
Additional advantages
The decision to use EPS as a fill material had some other benefits.
Although the modifications weren’t completed until March 2024, eliminating the need for demolition work and the construction of a new structure made the project shorter.
This was a key consideration for the Riveria City scheme. Any further delays in completing these works could have had a harmful impact on the whole development.
It also demonstrated that lightweight fill material can be a successful option in situations where there are concerns about gravity load or if there’s not enough conventional fill material.
This method could be particularly useful in highway projects that require conventional soil fill.
By introducing EPS, the project not only ensured the structure’s stability and functionality but also helped to make it more sustainable.
