STATIC PILE LOAD TESTS

By Jan MAERTENS, Jan Maertens BVBA and KU Leuven Noel HUYBRECHTS, WTCB

Introduction : Piles in dense sand layer Instrumentation (= extensometers) For each type: 2 piles with the same length Aim: determination of installation coefficients for this specific test site and pile type, to be integrated in NAD-EC7 • A certain number of piles have been excavated • • • •

Screw piles - Limelette II Cone Penetration Test: cone resistance qc (M Pa) 0

2

4

6

8

10

12

14

16

18

20

22

24

Friction ratio Rf (%) 26

0 1 2 3 4 5

D e p th (m )

6 7 8 9 10 11 12 13 14 15 16 17

Average CPT E (static test field)

28

Test Procedure: Scientific or common? • Scientific: – each load step is maintained till stabilisation – decreasing load steps when failure is approaching – => almost no influence of rate of loading – => accurate value of failure load • Common: – same test procedure as for normal control load tests – => same interpretation method as for normal control load tests

Common procedures: • STS 21: loading till 1,5 x service load and waiting for stabilisation at 1,0 and 1,5 x service load – = control of creep load

• NCP:loading in 8 steps till 2,0 x service load and waiting for stabilisation at each step – = control of creep load and bearing capacity – = very long tests

• LCPC-ISSMFE: loading in 8 steps till 2,0 x service load Each step is maintained for 1 hour – = control of creep load and bearing capacity – = within 1 working day

Adopted test procedure: - Loading in 8 to 10 constant steps Each step holded constant for 1 hour - Loading with 1/2 steps when failure appears to early (s < 25mm) - Value of loading steps determined based on available information - For the second pile of each type adapted ∆Q when necessary

Qmax

60' 60' 60'

10'

Pile Load Q

60' 60' ∆Q

60'

10'

60' 60' 10' 60' 60' 30' 0

1

2

3

4

5

6

Time (hours)

7

8

9

10

11

12

Pile

Failure during step n°

A1bis Fundex A2 Olivier A3 Omega A4 De Waal B1 Prefab B2 Prefab B3 Atlas B4 Atlas C1bis Fundex C2 Olivier C3 Omega C4 De Waal

13 8 + 1*0,5 8+ 3*0,5 7 + 3*0,5 9 + 2*0,5 11 8 + 2*0,5 R + 2*0,5 9 R + 3*0,5 5 + 1*0,5 (structural problem) 7 + 1*0,5 (structural problem) 9 + 3* 0,5 8 + 2*0,5

Results of each static load test : • Load - pile head settlement diagram • Variation of pile head settlement during the different load steps • Creep curve = increase of settlement during the last 30 min of each load step

S c re w p ile s - L im e le tte I I - S L T : P i le P il e B 2 - P r e c a s t P ile L o a d Q (k N ) 0

250

500

10 20 30 40

(m m )

P ile h e a d (s 0 ) & b a s e ( s b ) d is p la c e m e n t

0

50 60 70 80 s0

90 sb

10 0

75 0

1 00 0 1 25 0 15 00 17 50 20 00 22 50 25 00 27 50 3 00 0 3 25 0 3 50 0 3 75 0 4 00 0

S c re w P i le s - L im e le t te II S L T : P il e P i le B 2 -P r e c a s t

T i m e in m i n u te s (l o g a rit h m i c s c a l e ) 1

10

100

0

10

20

P ile h e a d d is p l a c e m e n t s 0 (m m )

30

40

50

60

70 S te p 1 ( 3 2 9 k N )

S te p 7 ( 2 1 3 1 k N )

S te p 2 ( 6 6 2 k N )

S te p 8 ( 2 6 4 2 k N )

S te p 3 ( 9 9 3 k N )

S te p 9 ( 2 9 7 3 k N )

S te p 4 ( 1 3 2 4 k N )

S te p 1 0 ( 3 3 0 4 k N )

S te p 5 ( 1 6 5 4 k N )

S te p 1 1 ( 3 6 1 6 k N )

80

90

S te p 6 ( 1 9 8 2 k N ) 10 0

S c re w p ile s - L im e le tte I I - S L T : P i le P il e B 2 - P r e c a s t

C r e e p : ∆ s i la s t 3 0 m in u te s (m m /3 0 m in .)

1 .5

1.25

1

0.75

0 .5

0.25

Q c = 2 89 0 k N

0 0

25 0

5 00

7 50

10 00 125 0 1 50 0 1 750 20 00 225 0 2 50 0 2 750 30 00 32 50 350 0 3 75 0 40 00

P ile L o a d Q ( k N )

Extrapolation of the first loading curve based on Chin curve Screw piles - Limelette II - SLT : PileB3-Atlas Pile Load Q (kN) 0

250

500

750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000

Pile head (s0) & base (sb) displacement (mm)

0 10 20

s0 sb extrap

30 40 50 60 70 80 90

100

Extrapolation the elastic deformation Screw piles - Limelette II - SLT : PileB3-Atlas

∆l = Pile head (s0) - base (sb) displacement (mm)

8 7 first cycle

6

polynom ial extrapolation

5 4 3 2 1 0 0

500

1000

1500

2000

Pile Load Q (kN)

2500

3000

3500

4000

Table 2 – Q corresponding to s0 = 10%Db: comparison between real measured values (Qs0 = 10%.Db) and extrapolated values by means of the Chin method (Qextrap,s0=10%Db). Qextrap,s0=10%Db Qextrap,s0=10%Db / Qs0 = 10%.Db Qs0 = 10%.Db Range s0 for CHIN Pile [kN] [-] extrapolation [mm] [kN] Fundex – A1bis 2988 3064 1.03 11.4 → 27.1 Omega - A3 2786 2772 0.99 16.8 → 32.4 Omega - C3 2723 2718 1.00 12.5 → 27.8 De Waal – A4 2400 2404 1.00 11.0 → 26.8 0.98 8.8 → 22.9 De Waal – C4 2248 2210 Precast – B1 2636 2649 1.01 9.5 → 34.9 Precast - B2 3476 4254 1.22 11.6 → 18.5 Atlas - B3 (3430)* 3528 (1.03) 24.0 → 35.5 * Atlas - B4 (3326) 3454 (1.04) 11.8 → 24.3 Olivier - A2 3354 15.2 → 31.0 Olivier - C2 2908 9.6 → 25.3 Fundex – C1bis 1778 8.6 → 27.2 * Values obtained from extrapolation of the load settlement curve (section 3.2.1).

Penetration rate at failure: - constant rate of penetration at failure was not possible

S c re w p ile s - L im e le t te II S L T : P il e A 1 b is - F u n d e x

T im e 9 :0 0

1 1 :0 0

1 3 :0 0

1 5:00

1 7 :0 0

1 9 :0 0

2 1 :0 0

2 3 :0 0

1 :0 0

-6

P ile h e a d v e lo c ity ( v 0 ) ( m m / m in )

-5 -4 -3 -2 -1 0 1 2 3 4 5 6

V0

Extensometer data: - Have been used during the loading to check pile shaft behavior - Will be used: • To deduce: – variation of load with depth within the pile – mobilisation of base resistance and shaft friction • Interpretation of measurements is very sensitive for: – corrections to be applied – value of EA • Values to be published after a detailed sensitivity

analysis

Extensometer readings during the static load tests Loading stopped when risk of failure S c r e w p ile s - L im e le tte I I - S L T : P ile B 4 - A tl a s P ile L o a d Q ( k N ) 0

250

5 00

75 0

1 000

12 50

1500

17 50

200 0 2 250

250 0 2 750

30 00

3250

3 500

375 0 4 000

0 p ile fa ilu re

10

u n l o a d in g s te p 9 20

a ft e r 2 m in u te s . R e m o val

30

e x t e n s o m e te r & re lo a d in g

40

(m m )

P ile h e a d ( s 0 ) & b a s e ( s b ) d is p la c e m e n t

R is k o n s tr u c tu r a l

50 S t ru c tu ra l

60

p il e f a ilu r e a ft e r 1 9

70

m inutes 80

in re l o a d s0

90 100

sb

step 11 34 19 kN

Example of extensometer readings S c r e w p i l e s L i m e l e t t e I I S L T :P i l e B 4 A t l a s

E x t e n s o m e t e r m e a s u r e m e n t s ( µ s t r a i n )

2 0 0 0 1 8 0 0 1 6 0 0 1 4 0 0

E X T 1

E X T 2

1 2 0 0

E X T 3

1 0 0 0

E X T 4

8 0 0

E X T 5

6 0 0

E X T 6

4 0 0 2 0 0 0 8 : 0 0

1 0 : 0 0 1 2 : 0 0 1 4 : 0 0 1 6 : 0 0 1 8 : 0 0 2 0 : 0 0 2 2 : 0 0 0 : 0 0 T i m e

2 : 0 0

Mobilisation of base and shaft resistance S c r e w p i le s - L im e le tt e I I - S L T

L o a d d is t rib u ti o n ( k N ) 0

2 50

5 00

75 0

10 00 12 50 1 50 0 17 50 20 00 22 50 2 50 0 27 50 30 00 3 25 0 3 50 0 37 50 4 000

0

P ile b a s e d is p l a c e m e n t s b ( m m )

10 20 30 40 Q 50 60 70 80 90 1 00

Qb Qs

Interpretation of the results : • Determination of the values Qmax, Q25mm, Q 0,10Db, Q 0.15Db and Qc

• Estimation of the allowable load R cal – – – –

R cal,1 = 0,8 . Qc R cal,2 = Q 0,10Db / 1,7 R cal,3 = Q 0,10Db / 2,0 => R cal,2 and R cal,3 are determinant for all piles

CALCULATED PILE BEARING CAPACITIES : Cfr. Belgian Practice (Holeyman et al, 1997) -

Ultimate base resitance:

Rbu = β . αb . εb . qbu(m) . Ab With : β = 1,0 αb = installation factor εb = parameter for stiff clays qbu(m) = ultimate unit pile base resistance according to the De Beer method Ab = nominal pile base cross section area

- Ultimate shaft friction: Total side friction increment ∆Qst has not been used Based on cone resistance: Rsu = ξ f . X s .∑ H i .qsui = ξ f . X s .∑ H i .η p qci *

With: ξf = installation factor ηp* = soil parameter qci = cone resistance

Remark: For all screw piles: Db = maximum diameter of the screw. For Fundex: Ds = maximum diameter of the tube For De Waal, Olivier, Omega and Atlas: Ds = maximum diameter of the screw

Remark: Calculations have been performed: - starting from electrical CPT tests - based on individual CPT’s

Comparison of total pile bearing capacityGlobal coefficient: Global coefficient = Q / R With: Q = measured pile head load R = calculated total bearing capacity

Global coefficient for a settlement of 0,10 Db 0,75 à 0,97 for screw piles 0,89 à 1,02 for driven piles

Based on ERTC 3 calculation method Screw Piles - Limelette II Q/Ru; ERTC3 1,4 1,3 1,2 1,1

Q/Ru; ERTC3 (-)

1 0,9 0,8 0,7 0,6 0,5 0,4 0,3

Precast driven : Screw piles : C2 (no sb meas.):

0,2 0,1 0 0

2

4

6

8

10 sb/Db (%)

12

14

16

18

20

Based on NA-EC 7 method Screw Piles - Limelette II Q/Ru; NA-EC7 1,4 1,3 1,2 1,1

Q/Ru; NA-EC7 (-)

1 0,9 0,8 0,7 0,6 0,5 0,4 Precast driven : Screw piles : C2 (no sb meas.):

0,3 0,2 0,1 0 0

2

4

6

8

10 sb/Db (%)

12

14

16

18

20

Other driven piles at Limelette test site Based on ERTC 3 calculation method Screw Piles - Limelette II + Driven piles Limelette I Q/Ru; ERTC3 1,4 1,3 1,2

Q/Ru;ERTC3 (-)

1,1 1 0,9 0,8 0,7 0,6 0,5 0,4

B1-Driven Precast Pile

0,3

B2-Driven Precast Pile

0,2

Pile 8 - Driven Precast Pile (Limelette I - 1995/1996)

0,1 0 0

2

4

6

8

10 sb/Db (%)

12

14

16

18

20

Conclusion 1 : • Proposal : – for driven piles: – for screwed piles:

αb = 1,0 αb = 0,8

ξf = 0,8 ξf = 0,8

• Assumptions: – qc from E1 cone – base resistance calculated according to De Beer method ( 0,20m steps) – considered diameters = maximum diameter of the screw/tube – failure criterion = 0,10 Db

Conclusion 2 : • When proposed installation coefficients are introduced in design calculations: safety factor of 2 should be applied on base resistance and shaft friction

Additional controls:

- Excavation of a certain number of piles - To check the pile dimensions - To find an explanation for some anomalies - Inclinometer measurements in the driven precast piles

DE WAAL C9

FUNDEX A1bis

OMEGA A3

ATLAS B4

OLIVIER C2

ATLAS Screw flanges loam

ATLAS Screw flanges compact sand

OMEGA C3

OMEGA A3

DE WAAL C9

Pile B4 Atlas

FUNDEX C1bis Segregation due to use of too dry concrete

S c re w p ile s - L im e le t te II S L T : P ile C 1 b is -F u n d e x

E x te n s o m e t e r m e a s u re m e n ts ( µ s tra in )

5 00 0 4 50 0 4 00 0 3 50 0

EXT 1 EXT 2

3 00 0

EXT 3

2 50 0

EXT 4 2 00 0

EXT 5

1 50 0

EXT 6

1 00 0 50 0 0 8 :0 0

1 0 :0 0

12:00

1 4 :0 0

1 6 :0 0 T im e

1 8 :0 0

2 0 :0 0

2 2 :0 0

0:00

OLIVIER C2 Grooving underside screw flange

OLIVIER C2

Volume of soil displaced by cutting tooth during withdrawal

Inclinometer Results - Driven Precast B2 pile Deviation (mm) -200 -150 -100 -50 0 1 2 3

depth (m)

4 5 6 7 8 9 10

Direction AA' Direction BB'

0

50

100

150

200

D

e

e

e

W

m

b

b

a

a

r

C

s

s

g

a

a

a

ie

x

t la

t la

fa

fa

liv

d

A

A

re

re

a

g

r

A

ie

x

e

W

m

O

n

P

P

e

O

u

D

e

liv

d

O

n

O

u

4

3

lC

C

4

3

2

is

2

1

4

3

b

C

1

B

B

B

B

lA

A

is

2

b

A

1

0

F

F

Rc a i ( k N )

S c r e w P ile s - L im e le tt e I I

3000

2500

2000

1500 Rca1 Rca2 Rca3

1000

500

F

F

e

W

C

C

4

3

2

is

4

3

2

1

4

3

1b

B

B

B

B

is

2

lC

a

aa

eg

r

C

s

s

b

b

ie

x

tla

t la

fa

fa

liv

m

O

O

D

A

A

re

de

P

re

A

A

1b

lA

a

aa

eg

W

m

P

e

un

D

O

r

A

ie

x

liv

de

O

un

s0 i (m m )

S c re w P ile s - L im e le tte II

12

11

10

9

8

7

6

5 s01 s02 s03

4

3

2

1

0

D

e

e

b

b

a

a

r

C

s

s

g

a

a

a

ie

x

e

W

m

a

t la

tl

fa

fa

liv

d

A

A

re

re

a

g

r

A

ie

x

e

W

m

O

n

P

P

e

O

u

D

e

l iv

d

O

n

O

u

4

3

lC

C

4

3

2

is

2

1

4

3

b

C

1

B

B

B

B

lA

A

is

2

b

A

1

0

F

F

sb i ( m m )

S c r e w P ile s - L im e le t t e I I

12

11

10

9

8

7

6

5 sb1 sb2 sb3

4

3

2

1

Screw piles - Limelette II Cone Penetration Test: cone resistance qc (M Pa) 0

2

4

6

8

10

12

14

16

18

20

22

24

Friction ratio Rf (%) 26

0 1 2 3 4 5

D e p th (m )

6 7 8 9 10 11 12 13 14 15 16 17

Average CPT E (static test field)

28

Inclinometer Results - Driven Precast B1 pile

Inclinometer Results - Driven Precast B2 pile

Deviation (mm) -80

-40

0

40

80

120

160

200

-200 -160 -120 0

1

1

2

2

3

3

4

4

5

5

d e p th (m )

d e p th (m )

-200 -160 -120 0

Deviation (mm)

6 7 8

-80

-40

0

40

80

120

160

6 7 8

9

9

10

10

11

11

12

12

13

Direction AA'

13

Direction AA'

14

Direction BB'

14

Direction BB'

15

15

200

Conclusies : mbt case study SKW & LIM • Verschillende sondeermethodes : ⇒ grote verschillen ⇒ afh. van grondsoort ⇒ M1-Cont : resultaten SKW niet veralgemenen ⇒ bijdrage NAD-EC7 (conversiefactoren) • Afleiding grondkarakteristieken uit tabel NAD ⇒ aanvaardbaar ⇒ correctiefactor CN te groot ? σ’v0< 50 kPa • Vergelijking met enkele courante correlaties ⇒ aansluiting