The Foundations of the Millau Viaduct

GeoSS
Singapore, 7 February 2012
The Foundations of the Millau Viaduct
François SCHLOSSER
Emeritus Professor.
Ecole des Ponts. Paris Tech
The Millau Viaduct
(the highest cable stayed highway bridge)
•
•
•
•
•
Presentation of the viaduct
Geological and geotechnical aspects
Foundations
Design of the foundations
Application of the observational method
during construction (‘interactive design’)
• Earthworks and retaining structures
1
The viaduct was completing the north to south A75 highway at the
deep valley of the Tarn river close to the Millau town.
Participants to the construction of the Millau viaduct
Owner (Concession)
:
EIFFAGE
Architect
:
Norman FOSTER (GB)
Consulting Engineer
:
SETEC
Contractor Part 1
:
EIFFAGE Public Works
Contractor Part 2
:
EIFFEL Metallic Construction
Consultants for the owner
:
Michel VIRLOGEUX
( Structures )
François SCHLOSSER ( Foundations)
Alain PICCARDI
( Welding)
Bernard FOUCRIAT
( Concrete )
2
The Normandy Highway Bridge
over the Seine river
Michel VIRLOGEUX : the great french Highway Bridge Designer
Dimensions of the viaduct
Length :
Highest pier :
2,460 m
245 m
Height of the metallic pylons :
(P2 )
90 m
Slightly curved : constant radius
3
Other main figures
• 343 m : maximum total height over the Tarn river.
• 8 spans : 6 of 342 m and 2 of 204 m.
• 360 MN of steel for the deck (5 times the Eiffel tower).
• 2,050 MN of concrete of which 1,250 MN of high
resistance concrete.
General view of the viaduct at the end of
construction
North
South
Pylons. Cables. Red metallic provisional piers (one being dismantled)
4
Structures of the viaduct
Steel deck
Concrete piers and abutments
CONSTRUCTION
OF THE PIERS
 Top view of the P2 pier close to
its full height
 The crane is linked to the pier and
raised in the same step
5
Contruction of the piers
Two views taken from the south
side :
At the beginning after the
construction of the foundations
(large concrete piles and raft);
At a medium state. A temporary
metallic pier in red is at the
beginning of construction;
Temporary metallic pier
 Raising
jacking. is performed by jacking
 New steel tubes are placed in the
frame located at the base.

6
Pushing of the deck and clamping over the Tarn river
Deck elements were assembled on the two sides of the valley.
Pushing of the deck was performed using special jacking apparatus (vertical and
horizontal movements) at the top of each pier and provisonal pier
Launching direction
Clamping
Launching direction
Installation of the pylon
Pushing of the deck : arrival on a provisional pier
7
View of the pushing from
the two north and south
abutments.
View after the clamping over the Tarn river
8
View taken from the south side after clamping
Close to the end of the
construction.
The pylons have been erected
and a part of the cables has
been put in place.
Due to an optical effect the
cables at the north side of each
pylon are not visible.
9
GEOLOGICAL
and
GEOTECHNICAL
ASPECTS
Geological cross-section
Colluvium
(relatively instable layer)
Marls
Limestones
Major faults
10
Geological map
Karst in limestone under the future south abutment C8
11
Very fractured limestone at the location of the C0
abutment
Karst in the fractured rock at the location of the
temporary pier 1
12
CLOSE TO PIER
P1 (Northern part):
Limestone with
embedded marl.
Fractured to very
fractured rock.
Fault 1m wide.
Excavation in the very stiff marl for construction of the P5 raft
13
Excavation at the pier P7 in colluvium and stiff marl protected
by a soil nailed wall.
Landslide at P7 in the colluvium overlying the marl
14
Slide in the colluvium
covering the marls :
1) View from the top of the
temporary pier n° 6.
2) A small embankment was
constructed close to the
foundation of the temporary
pier for building it.
3) Nature of the embankment
material : marl excavated for
the construction of the
platform.
4) The slide occurred on
13/12/2003 after of a very
rainy period.
FOUNDATIONS
(Piers, temporary piers, abutments)
15
Foundations of the piers
Pier P2 (Limestone)
Pier P5 (Marl)
Foundation of the pier P 4
16
Pier P2 : loads applied on the foundation
Weight
Wind :
(pier + pile cap) :
H L = 10.6 MN
N = 350 MN
ML = 885 MN.m
(pier+ pile + cap +
deck) :
H T = 12.5 MN
N = 400 MN
M T = 2 360 MN.m
Longitudinal view
Side view
Excavation of the
shafts and
placement of the
reinforcements.
17
View of the south C0 abutment
Excavation for the foundation the C0 (north) abutment
18
Construction of the C8 north abutment
DESIGN
OF THE FOUNDATIONS
19
Geological and geotechnical investigations
Core sampling, destructive drillings, log soundings, in situ & lab testing,
inclinometers, pile load tests, trial shafts.
Example of the P3 pier
Location of pier P3
(in a steep slope, on limestones, close to the slope)
The depth of the piles have been increased after investigations
investig
20
MECHANICAL PARAMETERS OF THE ROCKS
RMR
(Rock Mass Rating)
•Rc or σc (matrix) = unconfined compression
•RQD (drill core quality)
0≤ RMR≤ 105
•Discontinuities (spacing, orientation,
fill material)
•Ground water
___
RMR-15
σc .10 40
Modulus
(GPa)
Hoek (1996)
100
Critère de rupture : Failure criterium
__________
:
=> (φ,c) tangents
σ1 = σ3 + mσc .σs + sσc ²
E=
√
√
m (RMR) s (RMR)
LIMESTONES (Héttangien, Sinémurien)
(Carixien)
E= (5 to10 GPa) /(10 to20 GPa),
σc = 50 to 70 MPa
E= 20 to 60 GPa
σc = 80 to 100 MPa
(Bajocien)
MARLS
σc = 70 to 160 MPa
(Domérien, Toarcien, Aalénien)
σc = 10 to 15 MPa
E= 0,5 to 1,5 GPa
Pile load tests in the marls
Load - settlement curve
Qc = 5200 kN
Shaft friction – displacement curves
qs  520 kPa
Qu  8000 kN
21
Foundation designs
DEEP FOUNDATION
Elasto-plastic design
(Service Limit State) + ULS
DEEP FOUNDATION
(Ultimate Limit State)
PILED RAFT
Terrasol elastic design
(SLS)
1) Ministry design:
Base of the piles only
2) Concessionnaire design :
Base and transversal reactions
3) Most probable behaviour design :
Piles + cap contribution
CALCULATION OF THE CONTRIBUTIONS
FROM THE CAP AND THE PILES
FOXTA computer program (TERRASOL)
PILED RAFT FOUNDATION
1) Assumption of a rigid cap
2) Elastic behaviour of the ground loaded
by the cap and of the ground under the pile
base
3) Elasto-plastic law for the shaft friction
tangential stress 
4) Use of the soil displacements
due to Qc for evaluating the relative
pile/sol displacement y
5) Iterative calculation
6) No pile group effect taken into account
22
Tassement
[mm]
avr.-02
TASSEMENT CALCULE SEMELLE P6
CALCULATED SETTLEMENT
(mm) OF THE RAFT (Pier P6
juin-02 août-02
oct.-02
déc.-02 févr.-03
avr.-03
juin-03
août-03
oct.-03
Masse du béton [T]
déc.-03 janv.-04 mars-04
0
24000
-0.5
3
-1
20000
-1.5
2b
-2
16000
-2.5
-3
12000
-3.5
-4
8000
2a
-4.5
-5
4000
-5.5
-6
0
Fin de la construction de la pile
18m
Nord
21 m
Pile + Tablier
Calcul EEG-SIMECSOL
Calcul SETEC
Calcul TERRASOL
MASSE BA SUR SEMELLE
Settlement calculation of the P 6 pier foundation versus time assuming different
behaviour mechanisms
Distribution of the loads on the foundation
TERRASOL calculation
Pier P2 (limestone) : cap ( 62%) + piles ( 38%)
Pier P6 (marl)
Case 4
: cap ( 7%) + piles ( 93%)
: Piers and deck weight ( permanent load)
+ maximum lateral wind (temporary load)
23
APPLICATION
of the
OBSERVATIONAL METHOD
during construction
(INTERACTIVE DESIGN)
Observational method
(‘interactive design’)
1) Design with the most probable behaviour
2) Monitoring
3) Implementation and design of contingency actions
4) Definition of thresholds for the application of the
contingency actions
24
Application of the observational method to
the Millau Viaduct
1) Deformation calculation of the piles + cap system
2) Definition of thresholds
3) Study of contingency actions
4) Geological observation of shaft excavation :
 new values of RMR index
 adaptations (pile depth, ground treatment, etc )
5) Monitoring of foundation settlements and rotations
Threshold definitions
Settlements
Rotation 
Vigilance threshold
Theoretical slope
ds / dQ (Simecsol curve)
5. 10-4 rad
Alert threshold
Confirmation of exceeding of vigilance threshold
25
Application of the observational method.
Contingency actions
Geology
Marls
Monitoring and
surveying
means
Possible
treatments
Differential
and/or
total settlement
Horizontal
micrometric
inclinometers
and
levelling
Injection
(compaction,
compensation)
Local or global
nailing Piles /
micropiles
Horizontal
movement
and/or
rotation
Micrometric
inclinometrers
Piezometers
Vertical
inclinometers
Precise levelling
Ground
reinforcement
Drainage
Eathworks
Possible
anomaly
Possible drifting
Clay pocket
Or
High deformability
heterogeneity
Thin clay layer
Excess pore
water pressure
High thrust on the
foundation
Anchors
Reinforcement
Passive thrust
Pile cap settlement (P2 Pier founded on limestones)
Tassement
[mm]
avr.-02 juin-02
1
TASSEMENT SEMELLE P2
Masse du béton [ T ]
août-02
oct.-02
déc.-02 févr.-03
avr.-03
juin-03
août-03
oct.-03
déc.-03
60000
0
50000
-1
40000
-2
30000
3
-3
20000
-4
10000
-5
0
Fin de la construction de la pile
18m
Nord
27m
Tassement moyen
PI2SEMLNIVNO1
Masse BA
Tassement calculé
PI2SEMLNIVSE1
PI2SEMLNIVNE1
PI2SEMLNIVSO1
26
(Pier P6 founded on the marls)
Settlement of the pile cap
Tassement
[mm]
avr.-02
0
Masse du béton [T]
TASSEMENT SEMELLE P6
juin-02
août-02
oct.-02
déc.-02
févr.-03
avr.-03
juin-03
août-03
oct.-03
déc.-03
16000
14000
-1
12000
-2
10000
8000
-3
3
6000
-4
4000
-5
2000
-6
0
Fin de la construction de la pile Mise en place du tablier
Nord
18m
Tassement moyen
PI6SEMLNIVNO1
PI6SEMLNIVSO1
MASSE BA SUR SEMELLE
21 m
PI6SEMLNIVNE1
PI6SEMLNIVSE1
Tassement calculé
Rotation of the pile cap (P6)
ROTATION SEMELLE P6
rotation [mrad]
avr.-02
0.6
juin-02
août-02
oct.-02
déc.-02
févr.-03
avr.-03
juin-03
août-03
Masse du béton [T]
oct.-03
déc.-03
16000
14000
0.4
12000
Est
0.2
Sud
10000
0
8000
Ouest
-0.2
Nord
6000
4000
-0.4
2000
-0.6
0
Fin de la construction de la pile
18m
Nord
21 m
Mise en place du tablier
Rotation moyenne vers l'Est / l'Ouest
Rotation moyenne vers le Sud / le Nord
seuils
"MASSE BA"
27
Rotation of the pile cap P2
Masse du béton [T]
ROTATION SEMELLE P2
rotation [m.rad]
avr.-02
0.6
juin-02
août-02
oct.-02
déc.-02
févr.-03
avr.-03
juin-03
août-03
oct.-03
déc.-03
60000
50000
0.4
0.2
40000
Est
Sud
0
30000
-0.2
20000
Ouest
-0.4
Nord
10000
0
Fin de la construction de la pile
-0.6
18
Nord
Rotation moyenne vers l'Est / l'Ouest
seuils
27m
Rotation moyenne vers le Sud / le Nord
MASSE BA
Settlement of the pile cap P3
Settlement
(mm)
Mass
(ton)
The vigilance
threshold has been
exceeded during
2 1/2 months
3
28
Settlements of all pier foundations versus load
EARTHWORKS
and
RETAINING STRUCTURES
29
Soil nailed wall at the P7 pier platform
PLANE VIEW
A-A CROSS SECTION
Calculation of the soil nailed wall
30
P3 platform
Soil nailed wall and reinforcement for the construction of the pile cap
31
Tervoile reinforced soil wall at the edge of the P3 platform
32
Construction of the Tervoile soil reinforced wall
Conclusions
1) The main part of the total load is due to the piers
2) Settlement of the pier fondations during the total construction is less
than 1 cm. No rotation detected.
3) Respective contributions of pile cap and piles are very different in
marls and in limestones
4) Contrary to what was expected, problems where encountered with
limestones and not with marls
5) The RMR method is well suited for marls, but a little less for
limestones
6)) Measured and calculated settlements and rotations are in fairly
good agreement, but measured settlements in the limestones are
occuring by steps.
7) The most difficult pier foundation was P3
8) Interactive design is a safe tool for risk management
33
Conclusions
9) Excavations in the slopes led to some stability problems
10) As expected the colluvium layer covering the marls led to
xxxxstability problems
11) Temporary retaining structures have to be improved considering
xxxxthe required 120 years service life. Observational method will be
xxxxused
34