PGCU - Génie civil et urbain

Terrassements Durables - Ouvrages en sols traités – TERDOUEST

Managing the soil treatment for an optimal use of earthwork's material

Issues in future works, both in France and abroad, are to offer building owners mastering techniques of soil treatment so as to to reduce waste and cut costs. TerDOUEST's project proposed new issues and revisit the principles known in the guides, unknown at the beginning of the project.

How material properties are improved by treatment

Despite a controlled practice for many years, soil treatment with lime or hydraulic binders lack of knowledge about the mechanisms of cementation and the fact that at the same dosage treated materials may reach very variable performance, sometimes no performance or worse, swelling. This hazard creates risks for the client, which is characterized by cost overruns and / or delays..<br />The TerDOUEST's project allowed understanding the mechanisms for improving low soil features, thanks to the incorporation of lime or hydraulic binders.The aims are to reduce uncertainty by identifying, for example: the role of minerals in the soil, the influence of the preparation methods, the mechanisms triggering the cementation ... The project involves the issue of sustainability (what is the role of water on effective final performance) and environmental acceptance criteria. The results are used to assess or reduce the degree of risk.

It was important to bring knowledge in the mechanisms of improvement of soil properties after incorporation of lime or hydraulic binder (Module A). To do so, traditional investigations are pushed to the infinitely small nanoparticles in soil treated with the implementation of technical imaging by magnetic resonance. Four soil types were studied in the laboratory including two taken from the town of Héricourt (Haute-Saône, 70). Tests were performed in the laboratory to check the evolution of the mechanical performance over time when the material undergoes a repeated passage of water simulating infiltration of rainwater, or variations of groundwater (Module B). This laboratory approach was supplemented by auscultation old embankments, which allowed to get information on the behavior of soils treated under conditions of normal earthworks. The laboratory approach was completed by an approach of real size (Module C). The consortium has built a full-scale embankment with silt and very plastic clays to create a monitoring center on the behavior of treated soil. The embankment was equipped with many sensors in order to monitor in real time changes in water content, temperature, surface runoff ....
Scientific approaches were completed by an analysis of the environmental impact of a solution of soil treatment compared with a more conventional granular solution (Module D). This analysis was based on the definition of appropriate indicators and data mining from the site of the National Road 7 Chaingy-La Pacaudière including the number of vehicles, fuel consumption, working hours, the lime consumption etc. .... This work was complemented by the development of a method of analysis of geotechnical risk.

TerDOUEST project has highlighted some of the mechanisms governing the initiation and then stabilization of cementing that stiffens a lime-treated soil with or without hydraulic binders. The contribution of mineral phases composing this soil has been revealed and a chemical model that reproduces the appearance of the cement phases and the contribution of each mineral phase has been improved. Further work from this research is underway to understand the specific role played by calcium in the ionic exchanges. The factors governing the durability of structures were identified through laboratory studies and auscultation of old landfills. Thus, infiltration of rain water or fluctuations in the level of the water table may affect the cementation and can decrease performance if dosages are not sufficient and if earthworks methods are not enough efficient . These effects can be reduced through a better control of treatment works by incorporating the appropriate level of binder, by choosing a homogeneous stock of soil, by requiring more accurate runtime settings (grinding, compaction ...). Analysis of the effects of frost was not carried out as part of this project, three partners committed themselves to conduct this study with a CIFRE thesis (Navier Lhoist, SPTF).
The validation of the use of treated soil can rely on the embankment reference Observatory for in situ performance, built on the deviation of Héricourt (RD.438) in Haute-Saone.
The contractors and building owners will also have documents that use environmental impact indicators and establishing the geotechnical risks.

Soil treatment is a technique that reduces waste generation in earthworks and reduce the taking of non-renewable resources higher value added. The choice of this technique has consequences in terms of technical expertise, cost and environmental impact as may be seen in the civil engineering works or pavement structures. French Companies and designers now have evidence to answer questions from building owners. It remains to establish more precise tools for defining levels of performance depending on the aggressivity of the environment. The aging of treated soil was characterized with respect to hydraulic performance and will be extended to mechanical fatigue under cyclic loading. This work makes sense in a context where climate is changing and modifies the conditions for which the earthworks were designed. These questions are also important because today we look for longer life buildings with lower maintenance requirements

The knowledges gained through the project were presented during an international conference on 18 and 19 June 2013 on the theme of «soil treatment for Sustainable earthwork« with the support of IDRRIM (Institute of Roads, Streets in Infrastructure Mobility). The knowledges will help writing a separate document entitled «the teachings of TerDOUEST« in a collection of IDRRIM.
The works have made ??possible:
- 5 papers (including 2 under submission) in classified revues and 5 papers in mainstream publications
- 29 oral communications (16 during TerDOUEST colloquium)
- An instrumented observatory fill in Héricourt (70)
- 17 research reports including
- Two methodological documents on relevant environmental impact indicators and analysis of geotechnical risk
- 1 computer model simulating the development of cement phases and the contribution of minerals in the soil

Project coordination

Emmanuel MANIER (Université)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 1,066,769 euros
Beginning and duration of the scientific project: - 48 Months

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