1 2012-09-13
CAVITY REMEDIATION OF PYLON FOUNDATION
Jørgen S. Steenfelt & Michael Schunk COWI, Denmark
DGF 2012-09-13: Geotechnical monitoring & the observational method
Cavity remediation of pylon foundation
2 2012-09-13
CAVITY REMEDIATION OF PYLON FOUNDATION
Brief project description
Geology; focus on P4 pylon
Remediation & monitoring strategy
Result of grouting scheme
Result of pile load testing
Conclusions
Owner: Direction des Travaux Publics de la Wilaya de Constantine – DTP Contractor: Andrade Gutierrez – AG (Brazil)
Introduction - outline
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CAVITY REMEDIATION OF PYLON FOUNDATION
Project extent & description
4 2012-09-13
CAVITY REMEDIATION OF PYLON FOUNDATION
Project extent & description
Sidi M'Cid
Sidi Rached
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CAVITY REMEDIATION OF PYLON FOUNDATION
Project extent & description
756 m cable stayed bridge main span 259 m (80 m clearance)
10 km roads incl. accesses (13 over & underpasses)
4 km retaining walls 1 km with ground anchors (up to 33 m retained height)
Extensive cuts (up to 45 m) (ground anchors & soil nails)
Embankments and slopes (ground anchors & soil nails)
P4
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CAVITY REMEDIATION OF PYLON FOUNDATION
Geology and ground conditions
0 200 400 600 800 1000 (m)
700 600 500 (m)
Recent deposits, Travertine; Continental deposits
Weathered Marl; Marl; Marlstone
Limestone
Faults; creeping soils; cavities
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CAVITY REMEDIATION OF PYLON FOUNDATION
Seismic area; confusing geology
150 boreholes; 20 inclinometer tubes - SPT & pressuremeter testing
- ambiguous or misleading laboratory testing
Property characterisation of Marls - exposed or buried; with or without water - drained/undrained for static/seismic actions - site data ambiguous & - local comparable experience inaccessible - parameters for slopes and cuts a hot & difficult issue
Pylon pile design - undr. strength of Marl based on PMT/SPT ("soil") - strength of Marlstone/Limestone based on UCS (rock) - shaft and toe bearing (mobilisation degree) - influence from fault
Geology and ground conditions
8 2012-09-13
CAVITY REMEDIATION OF PYLON FOUNDATION
Pylon P4 foundation – 14 Ø2 m bored piles
Pylon P4 moved due to fault presence - very slow progress of bored piles in Limestone
Pre-drilling holes Ø178 mm (5 per pile) - water loss or cavity by drop of drill string - mapping of Limestone & Marlstone top by borehole data - cavity feature needs to be considered
Pre-drilling no benefit for progress
- re-think design with pile toe in Marlstone above cavity
- remedial measures to handle cavity feature
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CAVITY REMEDIATION OF PYLON FOUNDATION
Fault and cavity feature
Geophysical survey
Boreholes
50 m drop
F1
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CAVITY REMEDIATION OF PYLON FOUNDATION
Pylon P4 foundation – 14 Ø2 m bored piles N Hypothetical extent of cavity
feature
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CAVITY REMEDIATION OF PYLON FOUNDATION
Remedial measures – required
Rock socket min. 5 m into Marlstone - max: 45 MN load; 11.9 MN toe bearing
Excessive or variable pile settlement - weathered Limestone and cavity feature
Cavity extending outside foundation footprint - excessive foundation settlement
Pre-drilling holes both a blessing and a curse?
Transfer of pile loads through cavity
Grouting of cavity in foundation footprint++
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CAVITY REMEDIATION OF PYLON FOUNDATION
Remedial measures – piles schematically
Limestone
Marlstone
Weathered Limestone
Cavity
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CAVITY REMEDIATION OF PYLON FOUNDATION
Remedial measures – for piles
Re-drill pre-drilling holes
Install reinforcement (12 m)
Grout to bored pile toe level
Execute Ø2 m bored pile
Ø2 m
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CAVITY REMEDIATION OF PYLON FOUNDATION
Remedial measures – foundation per se
Drill "destructively" 40 m total length - Ø141 mm casing in Marl - Ø105-115 mm uncased
Pressure grout staggered - bottom part (12 bar) - cased part (gravity)
20 primary holes
26 secondary holes
Monitor excess grout take
Tertiary grouting?
15 2012-09-13
CAVITY REMEDIATION OF PYLON FOUNDATION
Result of micropile grouting - excess take
0
10
20
30
40
50
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Pile Number
average
95% upper limit
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CAVITY REMEDIATION OF PYLON FOUNDATION
Result of pressure grouting vs. sequence
0
5
10
15
P11
P16
P19
P18 P
1P
2P
6P
7P
8P
9P
4P
5P
3P
12P
13P
17P
10P
20P
9 b
isP
15P
14
Primary grout hole
average
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CAVITY REMEDIATION OF PYLON FOUNDATION
Result of pressure grouting vs. sequence
0
5
10
15
SP SQ SB SF SU SS SV SI SG SD SM SY SL
D (m3)
Secondary grout hole
average
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CAVITY REMEDIATION OF PYLON FOUNDATION
Evaluation: grouting of cavity
Discontinuous feature
Pile P4/3 most onerously affected
Max pressure grout take coincide with max micropile take
Primary: 1.9 ± 3.8 m3
Secondary: 1.1 ± 2.6 m3
Tertiary not needed
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CAVITY REMEDIATION OF PYLON FOUNDATION
Grouting result – versus hypothesis
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CAVITY REMEDIATION OF PYLON FOUNDATION
Axial pile load test using O-cells
Top down
O-cell
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CAVITY REMEDIATION OF PYLON FOUNDATION
Pile load test: verification of axial capacity
upper 26.1 m test pile (Ø2 m)
lower 1 m test pile (Ø2 m)
cavity feature 1-2 m high?
O-cells (Ø870 mm)
break in concrete
11 m
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CAVITY REMEDIATION OF PYLON FOUNDATION
Pile load test: test location and set-up
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CAVITY REMEDIATION OF PYLON FOUNDATION
Pile load test: verification of axial capacity
-30
-25
-20
-15
-10
-5
0
0 10 20 30 40 50
d
[mm]
Gross O-cell load [MN]
End of creep O-cell down
Max load toe
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CAVITY REMEDIATION OF PYLON FOUNDATION
Pile load test: verification of axial capacity
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50
d
[mm]
Gross O-cell load [MN]
End of creep O-cell up
Max load shaft
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CAVITY REMEDIATION OF PYLON FOUNDATION
Conclusions
No evidence of detrimental effect from cavity
Pile behaviour largely linear to max applied load
Extrapolated loads - 200 mm toe and >5 mm shaft 110 MN
- at or above concrete capacity
Close monitoring and observations
savings in time & money
26 2012-09-13
CAVITY REMEDIATION OF PYLON FOUNDATION
..and the pylon is actually being built!