DGF 2012-09-13: Geotechnical monitoring & the ......DGF 2012-09-13: Geotechnical monitoring & the observational method ... Result of grouting scheme ... Pile load test: verification

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


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

3 2012-09-13


Project extent & description

http://lerhumel.free.fr/Images/rhumel detourne.jpg

4 2012-09-13



Sidi M'Cid

Sidi Rached

http://lerhumel.free.fr/Images/rhumel detourne.jpg

5 2012-09-13



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

6 2012-09-13


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

7 2012-09-13


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


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

9 2012-09-13


Fault and cavity feature

Geophysical survey

Boreholes

50 m drop

F1

10 2012-09-13


Pylon P4 foundation – 14 Ø2 m bored piles N Hypothetical extent of cavity

feature

11 2012-09-13


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++

12 2012-09-13


Remedial measures – piles schematically

Limestone

Marlstone

Weathered Limestone

Cavity

13 2012-09-13


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

14 2012-09-13


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


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

16 2012-09-13


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

17 2012-09-13


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

18 2012-09-13


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

19 2012-09-13


Grouting result – versus hypothesis

20 2012-09-13


Axial pile load test using O-cells

Top down

O-cell

21 2012-09-13


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

22 2012-09-13


Pile load test: test location and set-up

23 2012-09-13



-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

24 2012-09-13



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

25 2012-09-13


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


..and the pylon is actually being built!

Documents

DGF 2012-09-13: Geotechnical monitoring & the ......DGF 2012-09-13: Geotechnical monitoring & the observational method ... Result of grouting scheme ... Pile load test: verification