Reference projects analysed using CESAR-LCPC

Génie Civil

CESAR-LCPC

Soils & Rocks

Tunnels applications

Structures

Concrete at early age

CESAR-LCPC: Tunnels applications

CESAR-LCPC has been used in many important tunnel projects (Groene Hart tunnel, Subway of Cairo, Channel tunnel.). It is renowned for its capabilities to model projects from simple 2D sections (plane strain or axisymetry analysis) to complex 3D intersections.

2D and 3D Mesh generation

Complex 2D and 3D geometries can be defined using professional CAD tools integrated in the dedicated pre-processor CLEO.

For instance, the 3D graphical user interface allows creating curved soils layers or constructing the intersection between arbitrary surfaces.

Part of a mesh showing the junction
of two tunnels (courtesy of Arcadis-ESG)

Mesh and displacements isovalues
Modeling of a gallery in the Mont Blanc tunnel
(courtesy of Ingerop)

The new version of CESAR-LCPC integrates also the possibility to directly import a geometry created with format DXF.

Tools for the creation of user-defined macros are available in the 2D and 3D graphical user interfaces. For problems with standard geometries or for variation studies, the user can parameterize the model definition using a script.

Mesh created on the basis of the user macro

Parameterized geometry definition
Script developed by itech for Vinci

Soils structure interaction: structural elements

Reinforcement systems such as bolts, nails, anchors, micropiles or geotextiles can be modelled using structural elements such as trusses, beams or shells.

Beam elements inserted
to model bolts

The structural elements are attached to the solid mesh and activated during the construction phases.

The post processor CLEO allows easy visualization of the beam forces on the model geometry. Below, forces in the bolts obtained after excavation are shown:

Normal force in the bolts
and plot of the shear stresses in the soil
after complete removal of confinement stresses

Plot of plastic strains drawn on deformed shape
after complete removal of confinement stresses

Another example of structural elements used to model soil reinforcement: the tunnel of Bois de Peu ( Doubs , France ) created by LCPC.

Mesh

Model of an umbrella-arch system
(arches in blue, inclusions in yellow)

Automatic generation of confinement forces with CESAR-LCPC

For excavation problems, the stresses initially present in the excavated block of soil are replaced by balancing "external" forces on the wall of the excavation. These confinement forces are removed gradually during the excavation phase(s). These forces have the following expression:

with

	vector of the confinement forces
	tensor of the initial stresses
	unit vector normal to the excavation wall
	ratio between 0 and 1 representing the loss of confinement to be applied in the considered phase.

The "initial" stresses used in the formula can be defined either from the field of geostatic insitu stresses or from the stress results obtained from a previous analysis phase.

For 2D models, the ratio l allows considering partial loss of confinement due to the arching effect in the vicinity of the tunnel face.

Evolution of the ratio

in the vicinity of the tunnel face

2D visualisation of excavation forces
Dialogue box for the definition
of excavation forces

For 3D models, the advance of the tunnel face and the arching effects are generally modelled. The ratio l can therefore be set to 1.

Plot of displacement isovalues

3D visualization of excavation forces

Bibliographical references

VOSSOUGHI K.-C., NASRI V., MAGNAN J.-P.
3D Modelling of long-term behaviour of tunnels and comparison of two excavation methods.
4th International Conference on Ground Improvement Geosystems.
Helsinki (Finland), 7-9 june 2000, 8 pages.

ROATESI S., SIMIONESCU O.
Numerical analysis of the evolution of a circular tunnel in a viscoplastic rock mass with an inelastic lining.
European Conference on Computional Mechanics
Munich (Germany), 31 August - 3 September 1999.

BERNAT S., CAMBOU B., DUBOIS P.
Assessing a soft soil tunnelling numerical model using field data.
Géotechnique 49, n° 4, August 1999, p. 427-452.

ULM F.J., ACKER P., LEVY M.
The " Chunnel " fire. II : Analysis of concrete damage.
Journal of Engineering Mechanics, March 1999, p. 283-289.

BERNAT S., CAMBOU B.
Soil-structure Interaction in Shield Tunnelling in Soft Soil.
Computers and Geotechnics, Vol. 22, n° 3-4, 1998, p. 221-242.

BERNAT S., CAMBOU B., SANTOSA P.
Modeling of soil-structure interaction during tunnelling in soft soil.
9th International Conference on Computer Methods and Advances in Geomechanics.
Wuhan (China), 2-7 November 1997, Proceedings Balkema, Vol. 2, p. 1377-1382.

IFTIMIE T., ROATESI S.
The numerical modelling of the shield tunnelling method: Calibration with in-situ measurements.
Journées d'études internationales : Les travaux souterrains - Des techniques et des hommes. International Conference: Underground Works - Techniques and Men
Chambéry (France), 21-24 octobre 1996, Compte-rendu AFTES/ AFTES Proceeding p. 145-150.

ANTAO A., LECA E., MAGNAN J.P.
Finite element determination of upper bound solutions for the stability of shallow tunnels, based on a regularization principle.
10th Danube-European Conference on Soil Mechanics and Foundation Engineering.
Mamaia (Romania), September 1995, Proceedings Vol. 3, p. 479-486.

DURAND J.P., DEFFAYET M., JASSIONNESSE C., REITH J.L.
Surface settlements in urban tunnelling works: Design approach for Toulon underground motorway crossing.
International Congress on Tunnelling and Ground Conditions.
Cairo (Egypt), 3-7 April 1994, p. 97-104.

04/1994 ATWA M., LECA E.
Analysis of groundwater seepage towards tunnels.
International Congress on Tunnelling and Ground Conditions.
Cairo (Egypt), 3-7 April 1994, p. 303-310.

ZELIKSON A.
Displacement field and limit loads on a tunnel: A simulation study using rods.
Infrastructures souterraines de transports, 1993, p. 71-77.

géotechnique, tunnels, fondations, structures, cesar-lcpc un logiciel pour le genie civil