Earthen noise barrier

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Earthen noise barrier

Noise pollution due to road and railway traffic is a large cause of concern within the dense urban fabric of the Netherlands. Traditional noise barriers to reduce such pollution are often made from resource-intensive materials such as concrete and steel, and exacerbate the division created by highways. Earthen noise barriers, made by robotic 3D spraying with shot earth, can serve as a sculptural and living part of any urban environment, and form a connection instead of a border within the city’s ecology. Unlocking the potential of robotic fabrication for earth construction, creates new opportunities for more effective and efficient noise barriers. Terrestrial is exploring this concept, by developing material, technology and process. As engineering partner, Summum Engineering supports this effort through complementary research and development, structural design and engineering and parametric modelling.

There is an incredible infrastructure in the Netherlands – unsurprising given the high population and economic density of the country. To maintain a livable built environment, huge stretches of noise barriers have been erected and are still in planning stages. These enclosures, these fortifications, are not only unsightly and made of environmentally damaging materials, but their design and manufacturing methodologies are hopelessly outdated. Existing products are the results and reflections of these methodologies, and no longer align with the explicit desire for green and sustainable construction. The continued large-scale development of noise barriers offers an exciting opportunity to bring about change.

How can noise barriers contribute to the quality of the built environment? Can a noise barrier be a robotically fabricated and living part of our landscape? Can such a sound barrier, erected on site from Dutch soil, be sculptural, and be part of its ecology, rather than fragmenting it?

This project, funded by the city of Rotterdam, addresses these questions by imagining a robotically fabricated earthen wall and aiming to realize its potential.

Geometry

The robotic spraying of earth allows for noise barriers that are acoustically and structurally performative in ways that conventional barriers cannot be. A design was developed for the Rotterdam Ring, as a showcase for the application of this technology and material. Its doubly curved shape is structurally optimized, acoustically informed and parametrically generated.

This serpentine sound barrier makes the wall more efficient than a flat wall in its resistance against wind, reducing the use of material further, making the environmental impact even lower. This geometry is a nod to 18th century brick `crinkle crankle’ walls, found in places like Slot Zuylen in the Netherlands, as well as to the ruled brick walls featured in the Church of Cristo Obrero in Uruguay, designed by Eladio Dieste, and the Sagrada Família schools in Barcelona, designed by Antoni Gaudí.

However, the design pushes these ideas further, due to the freedom of form that robotic spraying affords us. The corrugations in the barrier are fully doubly curved beyond ruled forms and also have a wave length larger than that of sound waves along the highway. The wall is also slightly tapered and inclined, to prevent sound waves from reflecting back horizontally. The material is dense and thick enough to render any remaining sound transmission non-existent. The thickness increases towards the base to even out the stresses throughout the wall, making optimal use of the strength of earth.

Material

Raw materials such as sand, gravel, clay and a stabilizer or binder are formed into a durable and sustainable building material. These materials can be sourced from suppliers, local soil, or local soil banks. In the latter cases, it can have a negative economic value and cut down on the need for transportation and storage. The concept is ecological, innovative and upcycles soil – an important material flow. Using earth, a natural material, the environmental impact can be reduced by up to 97% compared to conventional sound barriers.

Construction

For the construction of the sound barrier, a system for spraying earth is attached to robotic arms which can be programmed for any geometric inputs. Each robotic arm is a mobile system on tracks which can be handled remotely by an operator. The supply equipment is placed close to the robotic arm in order to reduce water and air pressure losses. The material is stored in silo tanks at the supply station, and along with a supply line, provide constant flow of material in the system.

The earth is then compacted by spraying onto the barrier in consecutive layers, producing a radial pattern. The pressure compacts the material such that it is comparable to low-strength concrete. Using robots to spray the material and building it up from the ground bypasses the need for formwork, and liberates the design from the need of simplicity and repetition.

Prototype

As part of ProRail’s ‘Meerjarenprogramma Geluidsanering‘ (MJPG) (multi-year programme noise mitigation), they aim to minimize railway noise by constructing 56 km of barrier in the coming years, with an expected environmental impact currently equivalent to the annual CO2 emissions of 2,500 households. To counter this, they’ve partnered with Rijkswaterstaat by setting up the ‘Innovatiepartnerschap duurzame geluidsschermen‘ (IPDG) (innovation partnership sustainable noise barriers) to reduce this impact with radically new solutions, whilst meeting acoustic and structural requirements.

Terrestrial is developing such a solution with its shot earth barrier, and has been able to showcase its technology in a field test along the InnovA58 living lab and innovation highway. Summum has developed a unique design for this field test to rise to ProRail’s challenge, that leverages the sustainability of earth material and the freedom of robotic fabrication. Through the use of calculus, the section of our barrier is such that it entirely avoids tensile stress, even under the pressure from extreme wind and passing high-speed trains. In turn, it eliminates the need for any reinforcement, anchoring, or concrete foundation. The wall only needs to be supported by a gravel foundation with a geogrid, all easily reusable. The barrier’s profile is specifically designed to direct sound towards the track ballast, serving as a natural noise absorber.

Conclusion

The 3D-printed, earthen noise barrier is an innovative solution to achieve low-carbon and circular noise barriers through digitization, robotics and compressed earth. The materialization and freedom of form results in important desirable characteristics over existing products by providing opportunities for efficient use of materials, ecological embedding, superior acoustic behavior and sculptural design. It offers a better alternative, and offers opportunities to improve the environment where the noise is kept out, by being part of that very ecology. The earthen noise barrier goes beyond existing frameworks to create functional landscape architecture. Robotization allows us to approach the built environment in a very different way, and to respond to design factors that are locally relevant. Instead of allowing mass production to determine the design, mass customization makes it possible to respond to local needs and thus achieve a sophisticated design.