Ifsttar PhD subject

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Title : APPLICATION OF CEMENT-MODIFIED SOILS (CMS) IN RETAINING WALL

Main host Laboratory - Referent Advisor GERS - CG  -  LENOIR Thomas      tél. : +33 240845785

Director of the main host Laboratory BLANC Matthieu  -

PhD Speciality Mécanique - Géotechnique

Axis of the performance contract 2 - COP2017 - More efficient and resilient infrastructure

Main location Nantes

Doctoral affiliation ECOLE CENTRALE NANTES

PhD school Sciences de l'Ingénierie et des Systèmes (SIS)

Planned PhD supervisor THOREL Luc  -  Université Gustave Eiffel  -  GERS - CG

Planned financing Thèse sur contrat  - Ifsttar

Abstract

The in-situ soils present in the right-of-way of civil engineering projects have generally mechanical characteristics inconsistent with stress rates generated by the infrastructure they have to support. To upgrade these materials and use it in geotechnical works, it is common to mix the soils with a few percent of hydraulic binders to improve their mechanical performances. Besides, this process has the advantage to minimize the environmental impact and to reduce the economic cost of the infrastructures. CMS is widely used in numerous civil engineering applications such as road construction, embankments, foundations, slabs and piles. Nevertheless, the design of elements made with cement-modified soils is empirical and those materials are rarely used in structure that need accurate calculations like retaining wall. In this kind of structure, it is required to know both its failure mechanisms and the materials constitutive laws to define its internal stability. The aim of the PhD works is to investigate the performances of retaining wall made with cement-modified soils. The preliminary defined technical and scientific approaches are the following:
Based on finite element modelling, the critical stress paths in a given structural configuration will be identified.
Those calculations will be used to design sensor planning and prepare a real scale retaining wall test slab made with cementmodified soil.
Simultaneously, the determined stress paths will be compare with stress paths generated by referenced laboratory tests performed on civil engineering materials to determine an appropriate test at the laboratory scale to design retaining wall.
In the laboratory, the mechanical characteristics of two cementmodified soils (including the material used for the test slab) will be investigated. Specifically, we will focus on defining constitutive laws of materials under static and dynamic solicitations. These laws will be implemented into numerical models to compare with results from the sensor measurements of the test slab.
By parametric studies (height, base width, front face angle, tapering the rear face) a technological break for the design of retaining wall will be proposed.
Within the framework of this study, academic publications in well-referenced scientific journals are expected.

Keywords : cement-modified soils; retaining wall; geotechnical engineering

Main host Laboratory - Referent Advisor	GERS - CG - LENOIR Thomas tél. : +33 240845785
Director of the main host Laboratory	BLANC Matthieu -
PhD Speciality	Mécanique - Géotechnique
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Nantes
Doctoral affiliation	ECOLE CENTRALE NANTES
PhD school	Sciences de l'Ingénierie et des Systèmes (SIS)
Planned PhD supervisor	THOREL Luc - Université Gustave Eiffel - GERS - CG
Planned financing	Thèse sur contrat - Ifsttar
Abstract The in-situ soils present in the right-of-way of civil engineering projects have generally mechanical characteristics inconsistent with stress rates generated by the infrastructure they have to support. To upgrade these materials and use it in geotechnical works, it is common to mix the soils with a few percent of hydraulic binders to improve their mechanical performances. Besides, this process has the advantage to minimize the environmental impact and to reduce the economic cost of the infrastructures. CMS is widely used in numerous civil engineering applications such as road construction, embankments, foundations, slabs and piles. Nevertheless, the design of elements made with cement-modified soils is empirical and those materials are rarely used in structure that need accurate calculations like retaining wall. In this kind of structure, it is required to know both its failure mechanisms and the materials constitutive laws to define its internal stability. The aim of the PhD works is to investigate the performances of retaining wall made with cement-modified soils. The preliminary defined technical and scientific approaches are the following: Based on finite element modelling, the critical stress paths in a given structural configuration will be identified. Those calculations will be used to design sensor planning and prepare a real scale retaining wall test slab made with cementmodified soil. Simultaneously, the determined stress paths will be compare with stress paths generated by referenced laboratory tests performed on civil engineering materials to determine an appropriate test at the laboratory scale to design retaining wall. In the laboratory, the mechanical characteristics of two cementmodified soils (including the material used for the test slab) will be investigated. Specifically, we will focus on defining constitutive laws of materials under static and dynamic solicitations. These laws will be implemented into numerical models to compare with results from the sensor measurements of the test slab. By parametric studies (height, base width, front face angle, tapering the rear face) a technological break for the design of retaining wall will be proposed. Within the framework of this study, academic publications in well-referenced scientific journals are expected.
Keywords :	cement-modified soils; retaining wall; geotechnical engineering

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