Sustainable futures
Turning China’s waste soil into the foundations of a greener construction industry
China’s booming construction industry produces huge amounts of waste soil, as excavators clear earth for building foundations and infrastructure. Now researchers are finding ways to make dirt pay, while protecting the environment.
Much of the earth dug up by excavators and removed by trucks from construction sites across China ends up in landfills or is sunk far out at sea. Both options are expensive and potentially harmful to the environment.
But now, researchers from the University of Nottingham Ningbo China are offering construction projects a greener alternative: turning waste soils into materials that can be used in the building process.
Dr Juan Wang, Associate Professor in UNNC’s Department of Civil Engineering, applied her expertise in soil mechanics to a recent highway project connecting the port cities of Hangzhou and Ningbo. None of the soil that was excavated from the construction site was wasted: instead, it was turned into strong, durable foundation materials.
The challenge lay in the nature of the soil, which in the Southeaster coastal areas of China tends to be very soft. Known locally as ‘dust,’ its particles are small (mostly less than 75 nanometres) and water content is very high, meaning that it is very weak.
"we found a way of improving the quality of the waste soil, making it strong enough to be used as a foundation material"
Professor Wang said: "Normally it would be impossible to build with it. The construction project was producing large amounts of waste soil: enough to cover a football pitch to a height of 60 metres. But we found a way of improving the quality of the waste soil, making it strong enough to be used as a foundation material, and able to support vehicles. This saved the project around 30 million RMB (£3.2m).”
The UNNC team’s technology involves two processes: one introduces an additive to make soil particles connect well, and a pressure filter to quickly remove most water; the other involves mixing the residual with binding materials and compacting them to achieve a better microstructure, thus making the material stronger still. A new binding material was introduced, which is produced in a quite different process from that involved in making cement, and has a much smaller carbon footprint.
The technique has been used to construct a long section of the Ningbo-Hangzhou highway. It has the potential to be used in other highway or railway construction projects - the challenge is to understand how soil characteristics vary in different regions. By understanding these mechanisms, the technology could be rolled out across the country.
Professor Wang has seen close-up how UNNC combines British and Chinese strengths in this research area: geotechnics and geotechnical engineering. After graduation she worked at the University of Nottingham in the UK as a research fellow and lecturer. Now at UNNC, her research focuses on transportation geotechnics.
She said: “UNNC is a very international university, which benefits from some of the strengths of both the UK and the Chinese education systems. And for researchers, it allows us a great deal of freedom to explore our research interests and find practical applications for them.”