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Accueil du site > Equipes de recherche > Géotechnique > Ouvrages géotechniques > Geotechnical structures

Geotechnical structures

The themes of this axis are the foundations, soil improvement and reinforcement, internal erosion in hydraulic structures, the calculation of structures, railways applications, tunnels in fractured rock and tectonized and unsaturated soils.

Foundations

(J. Canou, A. Corfdir, JC Dupla, R. Frank, JM Pereira, AM Tang)

The studies focus on the behavior of piles under cyclic loading (ANR SOLCYP and National Project SOLCYP, 2009-2014), the energy piles (ANR PINRJ Scholars, 2011-2014, and collaboration with IFSTTAR), the calculation of displacement of piles, the behavior of industrial floors and the development of new French design standards for shallow and deep foundations, compatible with Eurocode 7 (CNJOG of the AFNOR). Under the SOLCYP projects, the behavior of the soil-pile interface under large number of cycles has been studied from a physical modeling calibration chamber (B. Tali thesis defended in 2011 ; H. Bekki thesis started in 2010 and R. Muhammed started in 2011). The results allowed to highlight the phenomenon of cyclic hardening and provide empirical laws of evolution of the axial friction. The ANR PINRJ (2011 - 2014) project (AM Tang, JM Pereira and G. Hassen from Multiscale Modelling team) aims to study the mechanical behavior of energy piles foundations under thermo-mechanical cyclic loading. A small energy pile model was developed and experimental studies are associated with numerical simulations (N. Yavari thesis started in 2011). The behavior of industrial flooring tiles has been a CIFRE contract with the French Building Federation (Y. Bouassida thesis defended in 2010). Calculations of displacements are studied in the framework of a thesis co-supervised by the Ecole des Ponts and the University of Darmstadt, with the support of the Keller Company, on the behavior of flexible and rigid inclusions and mixed foundations (C. Bohn thesis started in 2011).

Soil improvement and reinforcement

(J. Canou, JC Dupla)

In this research topic, the studies focus on reinforcing soil by vertical rigid inclusions (ASIRI national project, 2006-2011) and on the enhancement of the loess soils grouting (collaboration with SNCF). An original device based on "1g axisymmetric" physical modeling was developed to study the mechanisms of load transfer for loads of fill type (controlled pressure) and pavement type (controlled displacement) (QA Dinh thesis defended in 2011). The results showed good agreement with the tests in the centrifuge of IFSTTAR in Nantes and in situ tests.

Internal erosion in hydraulic structures

(J. Canou, J.C. Dupla)

The ERINOH national project (2009-2013) focuses on the study of the mechanisms of internal erosion, which is a major cause of failure of hydraulic structures (dams and dikes). An original device ("flow line"), to simulate the phenomena experimentally blocking the flow of water through a permanent sealant was developed. Blocking criteria have been proposed based on the characteristics of the flow (pressure, flow, hydraulic gradient...), the rheological characteristics of the sealant, soil characteristics and injection protocol (QQ Truong thesis defended in 2012, with collaboration of C. Knight, Gers department - IFSTTAR)

Calculation methods for geotechnical works

(A. Corfdir)

Work is carried out on the fundamental aspects of calculation (coupling BEM / FEM, problems specific to 2D modeling) (collaboration with UMLV), and multiphase methods applied to the calculation of reinforced earth structures (with IFSTTAR). The effect of degradation by corrosion of reinforcement (collaboration with Terre Armée and IFSTTAR) was studied and allowed to make recommendations on the monitoring of structures (T. Chau thesis defended in 2010).

Railways applications

(J. Canou, A. Corfdir, YJ Cui, P. Delage, JC Dupla, JM Pereira, AM Tang)

The hydro-mechanical behavior of collapsible loess of TGV North line was studied in the thesis of J. Muñoz - Castelblanco (defended in 2011) with a new triaxial apparatus for the complete monitoring of the local state of unsaturated specimen (deformation, water content and suction). The effect suction and water content on some elasto-plastic characteristics were identified (yield surface and flow rule) and the properties of water retention were related to the microstructure of loess.

Another topic is the renewal of ancient railway lines. Within the FUI - Pole Advancity RUFEX project (2010-2013), the effectiveness of vertical columns of soil mixing for soil reinforcement has been investigated. The work focused on the behavior of the soil - column interface under cyclic loading and the mechanical behavior at the young age of soil - grout mixture (VC The thesis defended in 2009). The phenomenon of mud-pumping has been studied in the thesis of TV Duong started in 2010. The hydromechanical behavior of the constituent materials of ancient platforms has been investigated to meet the problems of drainage lines in dump areas (VN Trinh thesis defended in 2011). The dynamic behavior of these materials has been studied under a new CIFRE - SNCF started in 2012 (F. Lopez - Lamas). A new method for evaluating the platform bearing capacity from the wave velocity is developed in the post- doctoral fellowship of A. Dhemaied (started in 2012).

Finally, the dynamic behavior of reinforced earth structures is studied for building high-speed lines (JB Payeur thesis started in 2012).

Tunnels in tectonised grounds

(J. Sulem)

This research conducted in collaboration with the French research center for tunnels (CETU) focuses on the behavior of tunnels in altered and tectonized grounds that exhibit strong delayed anisotropic deformation. The research focuses on a thorough analysis of geological and geotechnical data from the ramp of Saint -Martin- la-Porte, (an exploratory gallery that will reach the base tunnel Lyon- Turin rail link) and on the analytical and numerical modeling of the response of retaining structures (TM Vu thesis defended in 2010, thesis MH Tran started in 2011).

Capillary collapse in unsaturated soils

(P. Delage, JM Pereira in collaboration with M. Vandamme and M. Bornert from the Multiscale Modelling team)

This project aims to characterize two scales of the capillary collapse of a sand subjected to humidification in oedometric conditions with the help of X-ray microtomography (JF Bruchon thesis started in 2010). Despite the high heterogeneity of the collapse, the behavior at the local level (distortion - moisture retention curve relationship) is similar to the average behavior observed at the macroscopic scale (testing sample).

Characterization of soils similar to Martian soils

(YJ Cui, P. Delage, J. Dupla, AM Tang)

As part of the future mission InSight (2016), which aims to a better characterization of the structure of the planet Mars, the interaction between a seismometer and the Martian soil is investigated in collaboration with the Institute of Earth Physics of Paris (Ph. Lognonné). Tests for the characterization of compressibility, shear strength and sonic velocities were conducted on various analogs of Martian soils of volcanic origin (Mojave desert).

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