Rising sea levels caused by climate change pose a threat to coastlines around the world. Hope is at hand however, in the form of an innovative precast concrete solution made right here in New Zealand.

Westlock Concrete Solutions Ltd (WCS), based in Northern Buller on the West Coast of the South Island, decided that it was time to stop retreating and start advancing!

With the aim of protecting New Zealand’s vulnerable coastline from the rising tide, the small Kiwi company has designed and constructed a trial seawall of interlocking hexagonal concrete blocks at Hector, 30 kilometres north of Westport.

BACKGROUND
Martin Hill, WCS’s Director of Sales and Marketing has first-hand experience of the damage caused by coastal erosion. After several attempts at protecting his own property with large boulders, he realized it did not offer a long-term solution.

“I was looking for a long-lasting fix,” says Martin. “So, I began to collaborate with a group of local residents, which fortunately included several engineers.”

Following much discussion WCS was established, and its collective experience and expertise led to the interlocking block design.

As the development process reached the engineering compliance and manufacturing stages, WCS partnered Busck Prestressed Concrete Ltd, one of New Zealand’s largest and most respected manufacturers of precast concrete products.

The outcome was an engineered interlocking hexagonal block, which when combined with the appropriate placement method creates a versatile and durable structure that offer over 50 years of protection against the unrelenting ocean.

MANUFACTURING CONSIDERATIONS
Research and development undertaken by WCS paid dividend during manufacturing and installation.

“There is a lot more to the product than meets the eye, and with the help of Busck, we have created a very high-specification marine grade concrete block,” says Martin.

Busck acknowledge that making the blocks was relatively simple, thanks to WCS’s attention to detail during pre-production trials.

“WCS ironed out a lot of creases during their early development work,” says John Marshall, Busck’s National Technical & Design Manager. “This combined with their willingness to share information about the challenges they had overcome meant we didn’t have to reinvent the wheel.”

Busck conducted its own trials at its Ashburton factory, which used in-house draughting and 3D modelling capability to experiment with reinforcing content and with different ways of connecting the blocks to maximize resilience.

“The concrete used in the blocks themselves has a low water/cement ratio and contains micro-silica to ensure compliance with the marine requirements of class C in NZS 3101 Concrete Structures Standard for a 50-year life,” says Marshall.

Westlock Concrete Solutions (WCS) and Busck Prestressed Concrete Ltd are proud of their interlocking concrete seawall system.

The blocks also have a concrete strength of 45 MPa, a F4/U3 surface finish, a minimum reinforcing cover of 60 mm, and returns as specified in NZS 3101.

“The partnership is working very well, with Busck providing the design certification and manufacturing component, and WSC the concept, installation and marketing.” says John.

INSTALLATION AND RESPONSE
The trial seawall, located near the tiny West Coast town of Hector, was built in a week using a single 12-tonne excavator.

The seawall consists of three different block types (base, standard and top), is five blocks high and 40 blocks long, totalling around 200, 2-tonne concrete blocks.

There were no issues in terms of gaining consent, with the West Coast Regional Council, along with the Department of Conservation, seeing tremendous potential in the system’s ability to combat coastal erosion.

Of particular appeal to the Council is that the system requires minimal maintenance, unlike the current practice of arranging large boulders to form temporary barriers, which in storm conditions can pose a danger to homes.

The community response to the trial wall has been very positive, with plenty of offers to assist during installation, as well as many admiring glances now that it is complete.

NEXT STEPS
The local community’s interest has been matched from further afield, with inquiries received from along the West Coast and around New Zealand, a response helped by 1 News filming a story on the ‘clever concrete invention’.

WCS hope that the success of the trial seawall will prompt regional, district and city councils to seriously consider the system in plans to address coastal erosion.

The return on investment from the WCS system is clear, with the value of properties in areas prone to the loss or displacement of land always under threat.

Furthermore, the peace-of-mind offered through a permanent solution to coastal erosion also encourages the development of surrounding areas, making for a win-win situation.

The economics are bolstered by the fact that Busck can manufacture the blocks at any of its seven facilities across New Zealand, from which transport to site can either be by truck or rail.

“Climate change will inevitably accelerate the rate of coastal erosion across New Zealand, creating a lot of stress for property owners and councils alike,” says Martin.

“WSC will look to raise awareness of the interlocking block system with territorial authorities and central government as well as amongst civil engineers, to ensure every erosion affected New Zealander has the option of a long-term solution.”

Taken from Concrete magazine.