The reuse of excavated natural soil by lime stabilization

Nowadays the availability of natural high-quality soil to be used as construction materials is more and more limited; soils are norenewable resources and, as such, they should be recycled as much as possible. In a sustainable perspective, geotechnical engineering can significantly contribute to reach the recycling goal via selecting ways to reuse excavated soil. The properties of fine-grained soils can be improved by adding lime as a stabilizing agent to get proper material characteristics. The main factors that affect soil-lime properties are the curing temperature, the type and amount of lime added, the characteristics of the soil to be treated, the preparation procedures and the curing time. Given the great number of variables, proper design of soil-lime mixtures involves an extensive laboratory testing program that is often overlooked, causing risks of failure for the earthwork. In particular, in the laboratory design phase, different soil lime proportions should be tested and different treatment conditions should be simulated, as highlighted by the results that will be presented. Moreover, given the above mentioned reasons it is imperative to identify a screening criterion which allows to optimize the mix-design procedure. A research project with the previously mentioned objectives is in progress. Results show useful correlations among the shear strength parameters of soil-lime mixtures and the main variables of lime treatment, derived by multiple regression analyses. Also the effects of different curing conditions on hydraulic properties of soil-lime mixtures are presented. The contribution of microstructural investigation techniques such as SEM, EDS and MIP turns out to be essential to analyse the results of geotechnical tests and to understand the behaviour of soil-lime mixtures, because chemical products are detectable at meso- and micro-scale. Also a method to monitor and study reactions progress based on pH measurements is described and discussed, as an opportunity to improve discussion and analysis of test results.