CE22 - Mobilité et systèmes urbains durables

Raw earth construction vulnerability regarding hydric conditions – VBATCH

VBATCH

Vulnerability of raw earth building with respect to hydric conditions

Main issues and general objective

There are 3 objectives :<br />- The analysis of the liquid water content on the mechanical behavour in rammed earth.<br /> We aim to characterize : compressive strength, Young modulous, cohesion and friction angles.<br />- The modelling of the hydromechanical behaviour, using the concept of effective stress, used in soil mechanics.<br />- The instrumentation of the structures be mean of a non-destructive way, in order to detect the repartition of water content into the earth. Resistivity methods (as used in geophysocal sciences) are chosen for doing that.

Our analysis is mainly experimental. We are interested on the study of hydro-mechanical coupling within raw earth used in construction, as rammed earth. Our approach is to perform different mechanical tests (simple or more complicated, as those used for soil mechanics, triaxial and shear test).
At the structural scale, we investigate the mechanical capacity and the rigidity of the structure under different hydric states.

The results we get for the moment concern :
- the quantification of humidity effect on the mechanical capacity, through uniform Hydric state applied by liquid-vapour equilibrium. We could get such results at the material scale and at the structural scale (small piles).
- weare also developing resistive methods of diagnostic for 3D humid state, namely for capillary rise phenomenon, where the capillary front could be well detected.

The following of the project aims to generalize the results concerning hdromechanical coupling at the structural scale, through the study of wallets submitted to capillary rise and to drying. We also aim to developp our geophysical method of diagnostic on the wallets (drying and humid damage).

* Abdulsamad, F., Revil, A., Prime, N., Gnonnoue, P. Y., Schmutz, M., & Plé, O. (2020). Complex conductivity of rammed earth. Engineering Geology, 273, 105697.
* Hydro-mechanical coupling on rammed earth material: drying experiment at structural scale, soumis à International Conference on Biobased Construction Materials 2021.

Because the energy and raw material consumptions need nowadays to be reduced, researches more and more deal with sustainable construction design, with a reliable stability. This project, VBATCH, addresses a critical issue which is vulnerability, with respect to hydric conditions, of a low environmental impact building material, namely raw earth. This research will be developed at the interface between energy approach and mechanical approach often adopted for this material, aiming to analyze hydric effects on the mechanical behavior and stability of earth building. The project will be led in three stages: the experimental analysis at the material scale for a uniform hydro-mechanical problem, experimental analysis at the structural scale for a heterogeneous hydro-mechanical problem and numerical modelling, adjusted from the material scale experiments and validated from structural scale ones. Furthermore, a solution for geophysical monitoring of hydric properties, namely water content, will be investigated not only for the needs of the project, but also to be applied by professionals for inspection and diagnosis of existing buildings.
The project presents 4 strong originalities: the adaptation of non-saturated soil mechanics concepts for experiments and modelling, the experimental campaign non only at the material scale but also at the structural scale, the investigation of hydric history influence in addition to hydric state influence and the adaptation of geophysical methods for continuous and non-destructive water content investigation.
The project will benefits from multidisciplinary skills, put in common for the same specific aim. This multidisciplinary work will be possible by the project leader (Noémie Prime) experience on the mechanical and hydric soil behaviour and by the complementary experience of the other permanent members of the team (Olivier Plé, André Revil, Anne Cécile Grillet, David Cloet).

Project coordination

Noémie Prime (LABORATOIRE D'OPTIMISATION DE LA CONCEPTION ET INGÉNIERIE DE L'ENVIRONNEMENT)

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.

Partner

LOCIE LABORATOIRE D'OPTIMISATION DE LA CONCEPTION ET INGÉNIERIE DE L'ENVIRONNEMENT

Help of the ANR 253,241 euros
Beginning and duration of the scientific project: February 2019 - 42 Months

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