Waterfront living, seaside views and access to water are highly sought after in Australia, making seawalls vital infrastructure. They are the first line of defence, protecting low lying waterfront infrastructure against adverse weather events and constant water movement including waves, currents, and tides.
Typically made from steel, rock, or concrete, seawalls are constructed to suit a variety of landscapes and conditions including ocean foreshores, lakesides and canal systems. They are essential for protecting foreshores against flooding and weakened ground conditions, which can destroy waterfront structures and put lives at risk.
Seawalls must be engineered correctly and constantly maintained if they are to adequately keep people and the surrounding environment safe; old or poorly constructed seawalls can be just as hazardous as the water they hold at bay.
The effect of deteriorating seawalls
Waterfront structures including public infrastructure, such as footpaths, are at the mercy of deteriorating seawalls which can be impacted by water ingress, cracks and subsidence. Mainmark’s ground engineering experts have witnessed firsthand the effects of a deteriorating seawall, including the compromised structural integrity of the Marlston Waterfront in Bunbury, Western Australia, due to ongoing tidal movements, and the degradation of an historic sandstone seawall that caused subsidence and potential collapse of a patio area facing Sydney Harbour.
Without suitable protection from waves and tides, or a long-term plan to mitigate the ongoing effects of water movement, waterfront structures may become unsafe and unviable for property owners, tourism operators and other businesses who rely on a location’s access and safety.
Another example was the ongoing subsidence threatening the structural integrity of the stone walls protecting the banks of Lake Burley Griffin, a lake in the heart of Canberra that is a popular attraction for both locals and visitors. The damage had impacted the nearby walking paths and park area, rendering them hazardous and unusable. An extensive lake wall renewal program was undertaken by the National Capital Authority (NCA) who engaged Mainmark to repair, strengthen and renew the stone wall and surrounding footpaths. In all three projects Mainmark was able to consolidate the soils, fill voids and re-stabilise the walls with an innovative resin injection solution.
What is the solution?
A properly designed, newly constructed seawall should last for many decades. However, once construction is complete ongoing monitoring and maintenance of seawalls is required due to the constant presence of moving water that may vary in intensity. Corrosives such as salt, can also put the structure at perpetual risk of erosion or shifting, which is why it is important to establish a long-term monitoring and remediation plan tailored to the type of seawall and surrounding conditions. Signs of deterioration include subsided sections of seawall and cracks in the walls or adjacent footpaths. Reinforcement or reconstruction should be undertaken immediately if it appears that sections of the wall are damaged, its footings have eroded, or the soil behind the wall has been weakened. For example, seawalls that are subject to strong tidal movements, or are constructed on top of loose or sandy soils, can be reinforced with specialised solutions, such as Mainmark’s Teretek engineered resin, an expanding polyurethane solution that can be injected directly into the seawall to re-support the structure, fill voids, and strengthen and consolidate underlying soils that are vulnerable to erosion.
As urban development continues to increase, seawalls will remain crucial elements for protecting high traffic waterfrontages. Using the right materials and reinforcement measures, a structurally sound seawall will allow communities to safely enjoy the waterfront lifestyle for which Australia is famous.
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