field studies on bearing capacity of vibratory and impact ... · field studies on bearing capacity...

Field studies on bearing capacity of vibratory and impact driven piles

Dipl.-Ing. Patrick Lammertz

Institute of Soil Mechanics & Foundation EngineeringEssen University, Germany

Introduction

Institute of Soil Mechanics & Foundation Engineering, University of Essen (Germany)

Engineering aspects related to the use of the vibratory and impact driving techniques:

• Driveability

- e.g. the penetration speed achieved versus depth

• Environmental impact

- e.g. the level of ground vibrations induced

• bearing capacity

- e.g. the prediction of bearing capacity from the driving log

- the bearing capacity of piles

Research Motivation


• The bearing capacity of vibratory driven piles cannot be calculated with sufficient accuracy based on the observed final rate of penetration

• A thorough literature study revealed that the bearing capacity of vibratory piles is up to 60% lower than impact driven piles

• Practice: vibratory piles are redriven with an impact hammer on the last meters for acceptance as a bearing pile

Research Objektive and Approaches


Main objektive

• Comparative investigations of vibratory piles to impact-driven piles concerning bearing capacity

• Determine the influence of vibro-driver parameters on the bearing capacity

• Investigate the soil plugging behaviour of vibratory driven piles

• Elaborate links between the results of the cone penetration tests and the driving log of vibratory driven piles

• Theoretical work

• Full-scale field studies

Approaches

Vibratory technique and the mode of action


Ω

at ac

Fc FvFh

Ω

atac

FcFvFh

( )2stdyn f2MF π⋅=

f Mst

Stationary part

Static surcharge force

Vibratory part

Sinusoidal excitation force

The soil resistance during vibratorydriving is lower than the bearing capacity

mode of action:

shear strength reduction

pile vibratory resistance bearing capacity?

Vibratory technique:

Field studies, pier construction


In-situ-concrete pile

Foundation:

Open-ended steel pilesL=31,3 m (27,5 m)∅= 914,7 mm, t = 12,7 mma =4,3 m

Combined sheet pile wall

Field studies, concept of test programm


recording of driving data influenced on the bearing capacity

of in-situ piles

WB 6*-14,1 mNN

2.10 (-16.20)fS, ms

4.10 (-18.20)f-mS

4.30 (-18.40) U, s, fg, t' 5.20 (-19.30) m-gS, fs, g

8.50 (-22.60)m-gS, fs, fg'

14.30 (-28.40)

f-mS

S f f '

0.70 (-4.70) U, _t, fs', h (Schlick)

1.50 (-5.50) H (Torf) 2.30 (-6.30) U,

_t, fs', h (Schlick)

3.40 (-7.40) T, u, _h (Schlick, Holzreste )

8.10 (-12.10)

U, _t, fs', h (Schlick)

9.10 (-13.10) fS, u', ms'

10.10 (-14.10) fS, ms

33917

33920

33923CPT-W18-14,1 mNN

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Spitzendruck [MN/m ²]

28

WB 6*-14,1 mNN

2.10 (-16.20)fS, ms

4.10 (-18.20)f-mS

4.30 (-18.40) U, s, fg, t' 5.20 (-19.30) m-gS, fs, g

8.50 (-22.60)m-gS, fs, fg'

14.30 (-28.40)

f-mS

S f f '

0.70 (-4.70) U, _t, fs', h (Schlick)

1.50 (-5.50) H (Torf) 2.30 (-6.30) U,


3.40 (-7.40) T, u, _h (Schlick, Holzreste )

8.10 (-12.10)


9.10 (-13.10) fS, u', ms'

10.10 (-14.10) fS, ms

33917

33920

33923CPT-W18-14,1 mNN

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40


28

Field studies, site investigations and laboratory tests

mNN

-39-38-37-36-35-34-33-32-31-30-29-28-27-26-25-24-23-22-21-20-19-18-17-16-15-14-13-12-11-10

-9-8-7-6-5-4

mNN

-39-38-37-36-35-34-33-32-31-30-29-28-27-26-25-24-23-22-21-20-19-18-17-16-15-14-13-12-11-10-9-8-7-6-5-4

0.0

10.0

20.0

30.0

40.0

50.0

Schlagzahlen Nk auf 30 cmSPT

26.0

37.0

29.0

WB 6*-14,1 mNN

2.10 (-16.20)fS, ms

4.10 (-18.20)f-mS

4.30 (-18.40) U, s, fg, t' 5.20 (-19.30) m-gS, fs, g

8.50 (-22.60)m-gS, fs, fg'

14.30 (-28.40)

f-mS

17.40 (-31.50)

mS, fs, gs, fg'

19.40 (-33.50)gS, ms, fg

23.90 (-38.00)

m-gS, fs, fg'

Schutzrohr-4,0 mNN

0.70 (-4.70) U, _t, fs', h (Schlick)

1.50 (-5.50) H (Torf) 2.30 (-6.30) U,


3.40 (-7.40) T, u, _h (Schlick, Holzreste)

8.10 (-12.10)


9.10 (-13.10) fS, u', ms'

10.10 (-14.10) fS, ms

33917

33920

33923CPT-W18-14,1 mNN

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40


0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

0. 0 0.1 0.2 0.3 0.4 0.5

Mante lre ibung [M N/m ²]

0 1 2 3 4

Reibungsverhä ltnis [%]

L egende Sp itzendrucksehr lockerlockermitteldich td ichtsehr d icht

212 Schl.

261 Schl.

287 Schl.

Nk > 4 = mitteldich tNk > 11 = dicht

Bohrkern SonderprobeDie Lage der Ansatzpunkte der Baugrund-erkundungen is t der Anl. 1.2 zu entnehmen .

*D ie Bohrung wurde im Ansatzpunk t der Drucksondierung abgeteuft .

28

29

30

31


Field studies, site investigations and laboratory tests


Schlämmkorn SiebkornSchluffkorn Sandkorn Kieskorn

Feinstes SteineFein- Mittel- Grob- Fein- Mittel- Grob- Fein- Mittel- Grob-

Korndurchmesser d in mm

Mas

sena

ntei

le d

er K

örne

r <

d in

% d

er G

esam

tmen

ge

0

10

20

30

40

50

60

70

80

90

100

0.001 0.002 0.006 0.01 0.02 0.06 0.1 0.2 0.6 1 2 6 10 20 60 100

2829

30

31

Schlämmkorn SiebkornSchluffkorn Sandkorn Kieskorn

Feinstes SteineFein- Mittel- Grob- Fein- Mittel- Grob- Fein- Mittel- Grob-

Korndurchmesser d in mm

Mas

sena

ntei

le d

er K

örne

r <

d in

% d

er G

esam

tmen

ge

0

10

20

30

40

50

60

70

80

90

100

0.001 0.002 0.006 0.01 0.02 0.06 0.1 0.2 0.6 1 2 6 10 20 60 100

2829

30

31

0

60

120

180

240

300

360

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

Sche

rspa

nnun

g τ

[kN

/m²]

100 kN/m²

300 kN/m²

250 kN/m²

200 kN/m²

450 kN/m²

350 kN/m²

-0,1

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

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

Scherweg Δl [mm]

Höh

enän

deru

ng Δ

h [m

m]

dicht

locker

0

60

120

180

240

300

360

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

Sche

rspa

nnun

g τ

[kN

/m²]

100 kN/m²

300 kN/m²

250 kN/m²

200 kN/m²

450 kN/m²

350 kN/m²

-0,1

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

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

Scherweg Δl [mm]

Höh

enän

deru

ng Δ

h [m

m]

dicht

locker

Field studies, used drivers

3,5 t (ram weight)

70 kNm (max. blow energy)

50 bl/min (blow rate)

IHC Hydrohammer S 70 MS 32 HFvar

f = 39,6 Hz (frequency)

Mst=32 kgm (eccentric moment)

Fdyn = 1976 kN (excitation force)


Scope of field studies

• 3 pile groups, each pile group consists of 2 pairs of piles

• 4 pairs of piles were tested for direct comparison on vibratory and impact driven piles

• 2 pairs of piles were installed with different vibratory parameters (frequency and eccentric moment)

Study encompasses the following investigations :

impact driven pilevibratory driven pileCPT


A1A2

Driving log, pair of piles A1

-25

-24

-23

-22

-21

-20

-19

0 10 20 30 40

cone resistance qc [MN/m²]

dept

h [

NN

+m

]

-24,5 mNN

vibropile

impactpile

-25

-24

-23

-22

-21

-20

-19

0 10 20 30

relating driving energy [MNm/m]

dept

h [

NN

+m

]

total Energy:Etot = 33 MNm

blow energy:Esp=56 kNm

set per blow: ~ 9 mm

-25

-24

-23

-22

-21

-20

-19

0 20 40 60 80 100

velocity [mm/s]

dept

h [

NN

+m

]

driving frequency:f = 35 Hz

eccentric moment:Mst = 24 kNm

driving parameter

excitation force:Fdyn = 1161 kN

R Rs Rb

Impact : 2054 1510 544Vibratory : 2286 1675 611

bearing capacityafter 13 d: [kN]


Driving log, pair of piles A2

R Rs Rb

Impact : 5251 4299 952Vibratory : 4753 3970 782

bearing capacityafter 15 d: [kN]

-32

-31

-30

-29

-28

-27

-26

-25

0 10 20 30 40

cone resistance qc [MN/m²]

dept

h [

NN

+m

]

-30,3 mNN

vibropile

impactpile

-32

-31

-30

-29

-28

-27

-26

-25

0 10 20 30

relating driving energy [MNm/m]

dept

h [

NN

+m

]

total Energy (final 5 m):Etot = 39 MNm

blow energy:Esp=47 kNm

set per blow: ~ 4,5 mm

-32

-31

-30

-29

-28

-27

-26

-25

0 20 40 60 80 100

velocity [mm/s]

dept

h [

NN

+m

]

driving frequency:f = 34 Hz

eccentric moment:Mst = 32 kNm

driving parameter

excitation force:Fdyn = 1460 kN


Conclusion and outlook


• Impact pile tested has a higher bearing capacity than vibratory piles in very dense sand

• Vibratory pile tested exhibits slightly higher capacity than impact piles in medium dense sand

• The results of two comparative field studies carried out on vibratory and impact driven piles have been presented

• Both vibratory and impact piles are unplugged in dense and medium sand

• Driving logs regarding the bearing capacity for vibratory piles have to be defined

• Reliable criteria for the design of vibratory piles are required,

i.e. links between cone resistance and the driving log of vibratory piles have to be developed

field studies on bearing capacity of vibratory and impact ... · field studies on bearing capacity...

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