GeoDuct, circular viaduct

Sustainable and circular viaducts

The climate crisis is imposing new demands and introducing new challenges. The concept of sustainability is changing in content, and it now includes the ambition to design and build in ways that ensure circularity. Producing, transporting, deploying and demolishing concrete and steel takes huge amounts of energy and raw materials, with all the accompanying emissions and harmful gases. The burden placed on the environment by construction is considerable.

Arches of sand

The building industry is responsible for 50% of all extracted materials in the European Union, 35% of total waste generation and 5-12% of CO₂ emissions. Greater efficiency in the use of materials would save 80% of emissions.[1] So it is crucial to use materials that are environmentally friendly and circular. Circular design means working with reusable materials and techniques that are geared to reuse.

Rijkswaterstaat (Directorate-General for Public Works and Water Management) has set itself the goal of making its construction work circular by 2030, as part of its aim of reducing the CO₂ emissions the entire national government produces by 49% by that year. But what does the circular future look like in practice? Answering that question requires a great deal of research and technological innovation. So Rijkswaterstaat is now stimulating the sector by means of various subsidies and competitions.

As part of a consortium of large and small companies, architectural studio ZJA has responded to the call to carry out research into circular viaducts. After a number of detours, the designers opted for the use of what are known as granular piles or geotextile encased columns (GECs), flexible tubes of seamless geotextile with sand poured into them, which are then braced in an arched form within a reinforced structure at ground level and thereby create a free span.

The concept is based on the elimination of the major emissions involved in the production of concrete and steel by the application of geotextile, which is made of recycled plastic and can itself be reused, in combination with local sandy soils. If the GeoDuct ever needs to be demolished, it can be recycled in its entirety. The sand from inside the geotextile becomes landscape again, while the plastic is removed and reused. So the circle is closed.

The research

Initial tests were done on a small scale to gain further insight into the natural arching of compressed sand. The granular piles used vertically in abutments – cylinders of geotextile filled with tamped sand – were tested for their capacity in horizontal applications and found to exhibit reliable arching. When Plaxis calculations showed this to be adequate, it was time to scale up.

The prototype

Now that an above-ground filling installation has been designed and built, an experiment can be carried out aimed at achieving a span of almost seven metres, between abutments of reinforced earth.

Sensors and regular inspection over several months allow the course of the experiment to be compared to the mathematical model. Once the results are in conformity with the calculations, GeoDuct will be ready for application in commissioned structures.

A new architectural idiom

It is a big step forward, making a bridge out of the land itself. Far from merely functional, its construction produces radical savings in CO₂ emissions and energy use, and furthermore offers the ideal opportunity to improve the surroundings ecologically as a result of the space created for animals and plants.

Architectonically this type of circular innovation raises fundamental questions. Here we see none of the design freedom traditionally offered by steel and concrete, and this in turn has consequences for the latitude available for the fitting of such infrastructure into the surroundings. Architects, in close collaboration with structural engineers, will have to develop a new architectural idiom, which, in its interaction with natural forces and processes, will shape this new technology.

Gallery

Competition: Rijkswaterstaat (Directorate-General for Public Works and Water Management)
Architect: ZJA
In collaboration with: Dura Vermeer, IV-Infra, Ploegam, Wagemaker, GeoTec Solutions and HUESKER
Jaar: 2021 - ongoing

Project: #1211

[1] Internal Market, Industry, Entrepreneurship and SMEs – Buildings and construction | Sustainability [Online]. Available at https://ec.europa.eu/growth/industry/sustainability/builtenvironment_ (accessed: 02 May 2022).