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Valorisation des sols urbains faiblement polluées dans les travaux de terrassement : le devenir des polluants dans les sols traités compactés

Abstract : This work fits in the protection of natural resources. It aims the valorization urban soils excavated during earthworks. Given their high degree of heterogeneity and disturbed history, urban soils remain poorly characterized from a geotechnical and environmental point of view. In addition, their specificities generally do not allow the application of currently available regulatory guides, the purpose of which is to supervise the reuse of materials in the fields of civil engineering. The first part of this work consisted of a geotechnical, chemical and mineralogical characterization of two urban soils. These soils were excavated more than one meter deep in the Paris region in an industrial area (in Boulogne Billancourt) and in an area near the Paris peripheral road (in Ivry-sur-Seine). This step made it possible to show some common characteristics: close geotechnical, gypsum (main support of sulfur and strontium), elements based on concrete and slags (magnetic and non-magnetic), important phases falling respectively to classifications (C1B5 / C1A1 according to the RTM), a remarkable content of organic carbon, significant amounts (in total content) of metallic trace elements and sulphates, and finally a complex composition with a natural and anthropogenic component evidenced by a test of sorting imported from the field of aggregates. This latter component comprises bricks, gypsum (main support of sulfur and strontium), concrete-based elements as well as slags (magnetic and non-magnetic), main phases respectively carrying the metallic and carbon phases. Using a linear regression approach, the distribution of anthropogenic artifacts was evaluated in the different soil size compartments, which allows understanding the natural processes of urban soil degradation (phase fragmentation accompanied by pollutant transfer).According to environmental regulations based on leaching tests, metallic pollutants do not exhibit critical mobility (leaching). However, these soils are not considered inert waste because of their high total organic carbon content and their excessive release of sulphates (the main soil pollutant), fluorine and antimony. The treatment with 1% lime for use in backfill has been validated, despite the mechanical performance required for road use after treatment with 5% cement and the suitability for treatment with the presence of disturbing pollutants (in especially sulphates). The permeability properties of compacted urban soils (OPN or OPM) with or without treatment have made it possible to study the transfer of pollutants under conditions close to those in situ. If the lime treatment seems to increase the permeability, the treatment with cement seems to strongly reduce it on certain test pieces (no flow below 5 kPa of hydraulic load). The treatments could also have an effect on the release of certain pollutants from the results of the leaching test at pH 12 with sometimes an inhibitory effect (for Ba, Sb, Mo Ni or As), sometimes an activating effect (for Cu or V or As). Finally, an immersion test on a monolith showing the diffusion of pollutants rather than their percolation under the effect of a hydraulic load completes the panel of experiments to observe the transfer of pollutants
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Katia Bellagh. Valorisation des sols urbains faiblement polluées dans les travaux de terrassement : le devenir des polluants dans les sols traités compactés. Géotechnique. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1025⟩. ⟨tel-01734542⟩

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