Compaction is the process by which a mass of soil consisting of solid soil particles, air, and water is reduced in volume by the momentary application of loads, such as rolling, tamping or vibration. When used as a construction material, the significant engineering properties of soil are its shear strength, its compressibility, and its permeability. Compaction of the soil generally increases its shear strength, decreases its compressibility, and decreases its permeability.

Soils are fundamental and ultimately finite resources that satisfy a great number of functions which are essential to sustainability and activities associated with construction works. Construction and demolition waste is one of the heaviest and most voluminous waste streams generated in the EU. It accounts for approximately 25% – 30% of all waste generated in the EU and consists of numerous materials, including excavated soils, concrete, bricks, gypsum, wood, glass, metals, plastic, solvents, and asbestos, many of which can be recycled.

In this work package, the focus is on the “chemo-mechanical treatment” of the existing soil, and the durability of the mechanical and chemical properties of this compacted soil.
The re-use of the existing soil emphasizes many important advantages, in terms of time, cost and natural resources:

• No need to excavate large quantities of materials to “dispose of” elsewhere;

• No need to send those materials in specific waste disposal sites in case of pollution in the excavated soil;

• No need to use aggregates from other sites to reconstitute a soil with adapted mechanical properties.

But it generates also some major issues that we need to address if we want to avoid new problems in the future:

• From a geotechnical point of view, it is easy to determine mechanical properties that the compacted soil has to obtain to sustain the building or construction to be made. It is also possible to control those mechanical properties after the compaction. But it is much harder to make any commitment about the durability of those properties during the decades of use of the site. How the treated compacted soil will age? Will it retain all its properties? What will be the impact of the weather, of the frost, of a varying water level?

• From a geoenvironmental point of view, a compacted soil does not include “new chemicals” which would be added in the case of a treated soil. But all components originally present are still there. If there was some kind of pollutant in the soil to be reused, where will it go? Will it stay in the soil during the compaction? And what happens next? Will it stay “enclosed” and stabilized or will it spread and contaminate its neighborhood?