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

Friction ratio Rf (%)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

Screw piles - Limelette II Cone Penetration Test: cone resistance qc (MPa)

De

pth

(m

)Average CPT E(static test field)

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

0 1 2 3 4 5 6 7 8 9 10 11 12

Time (hours)

Pile

Lo

ad Q

60'

∆Q

Qmax

10'

10'

10'

30'

60'

60'

60'

60'

60'

60'

60'

60'

60'

Pile Failure during step n°A1bis Fundex 13A2 Olivier 8 + 1*0,5A3 Omega 8+ 3*0,5A4 De Waal 7 + 3*0,5B1 Prefab 9 + 2*0,5B2 Prefab 11B3 Atlas 8 + 2*0,5 R + 2*0,5B4 Atlas 9 R + 3*0,5C1bis Fundex 5 + 1*0,5 (structural problem)C2 Olivier 7 + 1*0,5 (structural problem)C3 Omega 9 + 3* 0,5C4 De Waal 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 i le s - L im e le tte I I - S L T : P ile P ile B 2 -P r e ca s t

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

0 2 5 0 5 0 0 7 5 0 1 0 0 0 1 2 5 0 1 5 0 0 1 7 5 0 2 0 0 0 2 2 5 0 2 5 0 0 2 7 5 0 3 0 0 0 3 2 5 0 3 5 0 0 3 7 5 0 4 0 0 0

P ile L o a d Q (k N )

Pil

e h

ea

d (

s0)

& b

as

e (

sb)

dis

pla

ce

me

nt

(mm

)

s 0

s b

S c re w P i le s - L im e le t te II

S L T : P ile P i le B 2 -P re c a s t

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

1 1 0 1 0 0

T im e in m in u te s (lo g a rith m ic s c a le )

Pile

he

ad

dis

pla

ce

me

nt

s0

(m

m)

S te p 1 (3 2 9 kN ) S te p 7 (2 1 3 1 k N )

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

S te p 3 (9 9 3 kN ) 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 )

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

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

0

0 . 2 5

0 .5

0 . 7 5

1

1 . 2 5

1 .5

0 2 5 0 5 0 0 7 5 0 1 0 0 0 1 2 5 0 1 5 0 0 1 7 5 0 2 0 0 0 2 2 5 0 2 5 0 0 2 7 5 0 3 0 0 0 3 2 5 0 3 5 0 0 3 7 5 0 4 0 0 0

P ile L o a d Q ( kN )

Cre

ep

: ∆

si l

as

t 3

0 m

inu

tes

(m

m/3

0m

in.)

Q c = 2 8 9 0 k N

Screw piles - Limelette II - SLT : PileB3-Atlas

0

10

20

30

40

50

60

70

80

90

100

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000

Pile Load Q (kN)

Pile

he

ad

(s 0)

& b

ase

(s b

) d

isp

lace

me

nt

(mm

)

s0

sb

extrap

Extrapolation of the first loading curve based on Chin curve

Screw piles - Limelette II - SLT : PileB3-Atlas

0

1

2

3

4

5

6

7

8

0 500 1000 1500 2000 2500 3000 3500 4000

Pile Load Q (kN)

∆l =

Pile

he

ad

(s0

) -

ba

se (

sb)

dis

pla

cem

en

t (m

m)

first cycle

polynomial extrapolation

Extrapolation the elastic deformation

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).

Pile Qs0 = 10%.Db [kN]

Qextrap,s0=10%Db

[kN] Qextrap,s0=10%Db / Qs0 = 10%.Db [-]

Range s0 for CHIN extrapolation [mm]

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

De Waal – C4 2248 2210 0.98 8.8 → 22.9

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 I I

S L T : P il e A 1 b is - F u n d e x

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

9 :0 0 1 1 :0 0 1 3 :0 0 1 5 : 0 0 1 7 :0 0 1 9 :0 0 2 1 :0 0 2 3 :0 0 1 :0 0

T im e

Pil

e h

ea

d v

elo

cit

y (

v0

) (m

m/m

in)

V 0

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

S c re w p i le s - L im e le tte I I - S L T : P ile B 4 -A tla s

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

0 2 5 0 5 0 0 7 5 0 1 0 0 0 1 2 5 0 1 5 0 0 1 7 5 0 2 0 0 0 2 2 5 0 2 5 0 0 2 7 5 0 3 0 0 0 3 2 5 0 3 5 0 0 3 7 5 0 4 0 0 0

P ile L o ad Q (k N )

Pile

he

ad

(s

0)

& b

as

e (

sb)

dis

pla

ce

me

nt

(mm

)

s 0

s b

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

p ile fa ilu re

u n lo a d in g s te p 9

a ft e r 2 m in u te s .

R e m o v a l

e x t e n s o m e te r &

re lo a d in g

S t ru c tu ra l

p il e f a ilu re

a ft e r 1 9

m in u t e s

in re l o a d

s t e p 1 1 -

3 4 1 9 k N

Extensometer readings during the static load testsLoading stopped when risk of failure

Screw piles - Limelette II

SLT : Pile B4-Atlas

0

200

400

600

800

1000

1200

1400

1600

1800

2000

8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00

Time

Extensometer measurements (µstrain)

EXT 1

EXT 2

EXT 3

EXT 4

EXT 5

EXT 6

Example of extensometer readings

S c r e w p i le s - L im e le tt e I I - S L T

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

0 2 5 0 5 0 0 7 5 0 1 0 0 0 1 2 5 0 1 5 0 0 1 7 5 0 2 0 0 0 2 2 5 0 2 5 0 0 2 7 5 0 3 0 0 0 3 2 5 0 3 5 0 0 3 7 5 0 4 0 0 0

L o a d d is t r ib u ti o n (k N )

Pile

ba

se

dis

pla

ce

me

nt

sb

(m

m)

Q

Q b

Q s

Mobilisation of base and shaft resistance

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 = 1,0αb = 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: 

With: ξf = installation factor

ηp*

= soil parameter

qci = cone resistance

∑∑ == cipisfsuiisfsu qHXqHXR *...... ηξξ

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 capacity-Global coefficient:

Global coefficient = Q / R

With: Q = measured pile head loadR = calculated total bearing capacity

Global coefficient for a settlement of 0,10 Db

0,75 à 0,97 for screw piles0,89 à 1,02 for driven piles

Screw Piles - Limelette IIQ/Ru; ERTC3

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1,3

1,4

0 2 4 6 8 10 12 14 16 18 20

sb/Db (%)

Q/R

u; E

RT

C3

(-)

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

Based on ERTC 3 calculation method

Screw Piles - Limelette IIQ/Ru; NA-EC7

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1,3

1,4

0 2 4 6 8 10 12 14 16 18 20

sb/Db (%)

Q/R

u; N

A-E

C7

(-)

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

Based on NA-EC 7 method

Screw Piles - Limelette II + Driven piles Limelette IQ/Ru; ERTC3

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1,3

1,4

0 2 4 6 8 10 12 14 16 18 20

sb/Db (%)

Q/R

u;E

RT

C3

(-)

B1-Driven Precast Pile

B2-Driven Precast Pile

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

Other driven piles at Limelette test site

Based on ERTC 3 calculation method

Conclusion 1 :

• Proposal :– for driven piles: αb = 1,0 ξf = 0,8

– for screwed piles: αb = 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

OLIVIER C2

ATLAS B4

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

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0

3 5 0 0

4 0 0 0

4 5 0 0

5 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 im e

Ex

ten

so

me

ter

me

as

ure

me

nts

(µ

str

ain

)

E X T 1

E X T 2

E X T 3

E X T 4

E X T 5

E X T 6

OLIVIER C2

Grooving underside screw flange

OLIVIER C2

Volume of soil displaced

by cutting tooth during

withdrawal

Inclinometer Results - Driven Precast B2 pile

0

1

2

3

4

5

6

7

8

9

10

-200 -150 -100 -50 0 50 100 150 200

Deviation (mm)

dept

h (m

)

Direction AA'

Direction BB'

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

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0

F u n d e x A1 b is

Oliv

ier

A2

Om

e g a A3

De W

a a l A4

Pre

fab B

1

Pre

fab B

2

At la

s B3

At la

s B4

Fu n d e x C

1 b is

Oliv

ier

C2

Om

e g a C3

De W

a a l C4

Rc

ai (

kN

)

R c a 1R c a 2R c a 3

S crew P iles - L im e le tte II

0

1

2

3

4

5

6

7

8

9

10

11

12

Fundex A1b is

Oliv

ier A

2

Om

ega A3

De W

aa l A4

Pre

fab B

1

Pre

fab B

2

Atla

s B3

Atla

s B4

Fundex C1b is

Oliv

ier C

2

Om

ega C3

De W

aa l C4

s 0i (

mm

)

s 01s02s03

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

0

1

2

3

4

5

6

7

8

9

1 0

1 1

1 2

Fu n d e x A

1 b is

Oliv

ier

A2

Om

e g a A3

De W

a a l A4

Pre

fab B

1

Pre

fab B

2

At la

s B3

At la

s B4

Fu n d e x C

1 b is

Oliv

ier

C2

Om

e g a C3

De W

a a l C4

s bi (

mm

)

s b 1s b 2s b 3

Friction ratio Rf (%)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

Screw piles - Limelette II Cone Penetration Test: cone resistance qc (MPa)

De

pth

(m

)Average CPT E(static test field)

Inclinometer Results - Driven Precast B1 pile

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

-200 -160 -120 -80 -40 0 40 80 120 160 200

Deviation (mm)d

ep

th (

m)

Direction AA'

Direction BB'

Inclinometer Results - Driven Precast B2 pile

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

-200 -160 -120 -80 -40 0 40 80 120 160 200

Deviation (mm)

de

pth

(m

)

Direction AA'

Direction BB'

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