1

New Developments in Pile Foundations

K. Rainer Massarsch

2

Overview of Presentation

Auger Cast Piling (CFA) MethodRisk of Soil De-compressionMonitoring of Auger Cast Pile InstallationAuger Cast Pile with Expander Body Displacement Auger PilesVibrated Steel Piles with Expander BodySettlement-reducing Conical Concrete Nails

International DFI Conference – Stockholm 2014

3

Auger Cast Pile (CFA-pile)

Start of auger penetration

4

Auger Cast Pile (CFA-pile)

Auger penetrationSoil heave on ground surface

5

Auger Cast Pile (CFA-pile)

End of auger penetrationCompetent layer has been reached

6

Auger Cast Pile (CFA-pile)

Start of grouting processduring auger extraction

7

Conventional Auger Cast Pile (CFA-pile)

8

Auger Cast Pile (CFA-pile)

9

Small and Large Stem Auger

10

Decompression due to low penetration speed

Stiff layer

11

Decompression due to high extraction speed

Risk of necking

12

Risk of Soil Decompression during Penetration

d l

D

vcrit

Volume of stem

Volume of stem and flight

Volume of pumped soil

Critical penetration rate

n

13

Critical Penetration Speed – Soil De-compression

No de-compression

De-compression

14

Monitoring of Pile Installation

PENETATION

• Pushing force• Penetration speed• Torque• Hydraulic

pressure

EXTRACTION

• Concrete pressure

• Concrete volume• Extraction speed

15

Illistration of Installation Record

16

Determination of Pile Penetration Resistance

From drilling parameters the actual soil resistance is determined.

This information is used to establish required depth of penetration

Required pile length

17

Installation of Reinforcement

Placement of reinforcement can be critical for auger pile quality!

Single bar – cage – fibre concrete?

• Insertion procedure can damage borehole wall

• Full pile reinforcement may not be necessary

• Use straight reinforcement cage• For long piles: use guiding tube• Use vibrator if necessary• Large-stem piles facilitate

installation• Fibre concrete avoids problems

18

Applications of Expander Body

Expander Body can be combined with

conventional piling methods:

• Vibrated steel tube pile

• Continuous flight auger pile (CFA)

19

Pressuremeter Test

20

Inflation of Expander Body

Expander Body similar to

Pressure Meter Test

Grout volume and inflation pressure are

measured

21

After Expansion

TYPE LENTH DIAMETER TOE BEARING

AREA

SKIN AREA

VOLUME

m m mm2 mm2 m3

EB 610 1.0 0.6 0.28 1.43 0.21

EB 612 1.2 0.6 0.28 1.83 0.27

EB 615 1.5 0.6 0.28 2.38 0.36

EB 815 1.5 0.6 0.50 3.17 0.63

EB 820 2.0 0.8 0.50 4.42 0.88

22

EB Grouting Recording

23

Grouting Pressure and Grouting Volume, EB 600

Filling of EB

Expansion of EB

Soil displacement

Expansion pressure

24

Post-grouting of Expander Body

Post-grouted Zone

Expander Body shortens during

inflation

Inflation of Expander

Body

Full expansion

of Expander Body

25

Auger Cast Pile with Expander Body

26

Advantages of CFE + EB

Reduced pile lengthKnown shape of pile baseRecompression of soil at and below pile basePost-grouting of pile base avoids soil de-

compression Reduce pile shaft diameterQuality monitoring and control

27

Vibration Pile Test with Expander Body

Allermöhe, GermanyExpander

BodySteel tube piles12 and 16 m long

28

Comparison Steel Tube Pile and Expander Body Pile

ExpanderBody

Steel tubepile

Medium dense sand

Loose sandOrganic layers

29

Comparison Steel Tube Pile and Expander Body Pile

ExpanderBody

Steel tubepile

Medium dense sand

Loose sandOrganic layers

Steel tube pile

ExpanderBody

30

Design of Bearing Capacity based on CPT

Swedish Design Recommendations

EB toe resistance: Sand: sBase = 0.5 qc < 5MPaSilt and clay: s Base = 1.0 qc

EB shaft resistance: sShaft = 0.005 qc<50 kPa

D

qc

D

3D

31

Bearing Capacity from CPT Test

SHAFT RESISTANCE

TOE RESISTANCE

32

Installation of Vibrated EB Pile

33

Pile Test Loading

34

Steel Tube Pile vs. Expander Body

Pile length: 12 m

35

Advantages of Vibrated Steel pile with EB in Friction Soils

Quick and environmentally-friendly installation

End-driving to “set” not required as EB compresses soil

Known shape of pile basePost-grouting of pile base avoids soil de-

compression Quality monitoring and control

36

Gewerbehof Halle, Germany

37

Vibrated Conical Nails – Halle Business Center, Germany

Difficult ground conditions with variable fill material

Installation close to existing buildingConical concrete nails vibrated to 9 m depthHigh driving frequency (38 Hz)Vibro-compaction at end of nail installationLoad testing of concrete nail capacity

38

Settlement Reduction by vibrated Concrete Nails

Alternative foundation

solution to stone columns or piles

39

Cone Penetration Test, CPT

Cone Resistance, MPa

Friction Ratio, %

De

pth

, m

Mixed fill

Dense sand

Stiff clay and

lignite

Medium dense sand

40

Design Concept of Conical Nail Foundation

Determine settlement of unimproved ground using tangent modulus method

Are the calculate settlements acceptable? Calculate load which corresponds to acceptable

settlement Calculate the excess load to be supported by conical

nails Determine the number and distribution of conical nails

This design approach achieves load-sharing with nail safety factor FS =1.0!

41

Load from Surface Foundation

Increasedconfiningstress aroundnails

Q

Load fromnails

Load fromfooting

2

1

Load from Footing

42

Load-sharing between Surface Foundation and

Concrete Nails

Increasedconfiningstress aroundnails

Q

Load fromnails

Load fromfooting

Load from Concrete

Nails

Load from Footing

Factor of Safety of Concrete Nails

Fs = 1.0

43

Ground Vibrations During Vibratory Pile Driving

44

Variable Frequency Vibrator

NO ECCENTRIC MOMENT DURING START-UP AND

SHUT-DOWN OF VIBRATOR

45

Variable Frequency Vibrator

STRONG VIBRATIONS DURING DRIVING PHASE

46

Avoids resonance peaks of ground vibrations!

Resonance-free driving

47

Conical Concrete Nails

48

VIBRATION-MONITORING

INSIDE BUILDING

ELECTRONIC PROCESS CONTROL

VIBRATOR MS100

VIBRATION MONITORING

UNIT

CONCRETENAIL

49

Monitoring Resonance Compaction

Geophone

50

Installation of Concrete Nail

51

Frequency vs. Ground Response

0

2

4

6

8

10

12

14

16

18

5 10 15 20 25 30 35

FREEQUENCY, Hz

VE

RT

ICA

L P

AR

TIC

LE

VE

LO

CIT

Y, m

m/s

ResonanceFrequency

Penetration Frequency

Extraction

Frequency

Penetration

Frequency

Compaction

Frequency

52

0

100

200

300

400

14:22:26 14:23:18 14:24:10 14:25:02

Time, hrs:min:sec

Pressure, bar

0

10

20

30

40

Frequency, HzDepth, m

Velocity mm/s

Pressure bar Frequency Hz

Depth m Geo z mm/s

Example of Compaction Monitoring

Pressure MPa

Pressure MPa

40

30

20

10

Time h:m:s

53

Concrete Nails after Installation

54

Load Test of Concrete Nail and Steel Tube Pile

55

0

0,5

1

1,5

2

2,5

0 50 100 150 250 300 350

LOAD, kN

DE

FO

RM

AT

ION

, mm

Steel tube

Concrete Nail

Results of Loading Test

56

Advantages of Vibrated Concrete Nails

Can be installed efficiently in most soils by vibrator

Conical shape and small toe reduces driving resistance

Conical shape increases soil compactionConical shape provides high lateral

resistance near ground surfaceKnown shape and material properties

57

Thank you!