The use of cohesive soils improved with lime as an example of circular economy in earthworks

A common practice in civil engineering during earthworks is the usual replacement of cohesive soils (fine soils), excavated during earthworks, with non-cohesive soils (coarse soils). Until recently, such a procedure was dictated primarily by economic and technical reasons. From an economic point of view, the ease of access and therefore low cost of using such soils instead of cohesive soils was crucial. The technical reason is, above all, the ease of compacting fine soils (as opposed to cohesive soils) and well-developed and well-known engineering methods for controlling their compaction. The situation changed radically when the new environmental regulations came into force and enforcement by the inspection authorities began. Currently, soil removed from a construction site according to regulations should be classified as waste. This fact has completely changed the approach of participants in the construction process to the use of local soils, especially cohesive soils (e.g. clays). Their use "on site" has stopped being an expensive option and has become a necessity. This paper presents aspects of the use of lime-improved cohesive soils that can be successfully used on site as excavation backfill. Problems related to the proper preparation of soil-lime composites are described, as well as the results of compaction tests. The paper presents the author's own methodology for selecting the content of quicklime in the soil-lime composite.