ANALISI E PROGETTAZIONE DELLE FONDAZIONIadpaloha.altervista.org/wp-content/uploads/2012/11/PDF_0607.pdf · Fondazioni superficiali (1) Lezione 2 Quadro normativo di riferimento Lezione

Struttura del corsoStruttura del corso

VERIFICA FINALELezione 11Ottimo progettuale

Lezione 10Carico limite di piastre su pali

Giovedì06.03.08

Esercitazione 3Piastre su pali in condizioni di esercizio

Lezione 9Criteri innovativi di progettazione

Lezione 8Comportamento di pali in gruppo

Giovedì28.02.08

Esercitazione 2Pali soggetti a carichi trasversali

Lezione 7Sperimentazione su pali (2)


Giovedì21.02.08

Esercitazione 1Fondazioni soggette a carichi verticali

Lezione 5Pali soggetti a carico assiale

Lezione 4Fondazioni superficiali (2)

Giovedì14.02.08


Lezione 2Quadro normativo di riferimento

Lezione 1Criteri generali di progettazione

Giovedì07.02.08

15.00 – 17.3012.30 – 13.3010.30 – 12.00

ANALISI E PROGETTAZIONE DELLE FONDAZIONIANALISI E PROGETTAZIONE DELLE FONDAZIONI

Università degli Studi di Napoli Federico IISeconda Università degli Studi di NapoliUniversità degli Studi di SalernoUniversità degli Studi di Napoli ParthenopeUniversità degli Studi del Sannio

Università degli Studi Roma La Sapienza

Dottorato di Ricerca in Ingegneria Geotecnica

In fact, the designof piles is a rathercomplex matter….

State of the ArtReport

Analisi e progettazione delle fondazioniAversa, febbraio-marzo 2008

Alessandro MandoliniSeconda Università di Napoli

In fact, the design of piles is a rather complex matter,..

As all “complex” things, it should be composedby a real part and an imaginary part

The real part may be the experimental evidence

The imaginary (imaginative?) partthe models and methods of analysis



Selected topics in the field of pile foundations are addressed

State of the ArtReport



All engineering design involves the choice of a solution to a particular problem which is EFFECTIVE, PRACTICAL and ECONOMIC.

These objectives apply to piling as to any other item.

• ENGINEERING REQUIREMENTS

• CONVENIENCE

• SPEED OF ACTION

WHY PILES SHOULD BE CHOSEN FOR A PARTICULAR CASE ?



OBJECTIVES

• EFFECTIVE

• PRACTICAL

• ECONOMIC

To be effective, piles must carry the loads which the supported structure imparts to them, together with any additional forces which may result from deformations of the soil mass in which they are embedded (consolidation, earthquake, movements induced by nearbystructures, ……).



OBJECTIVES

• EFFECTIVE

• PRACTICAL

• ECONOMIC

To be practical, piles must be of a such type as will permit access for piling equipment to the locations where they are required. The design must recognize the limits of what is possible in current practice in terms of the equipment available and the method of construction must recognize and seek to minimize the difficulties related to ground conditions which could impede proper construction.



OBJECTIVES

• EFFECTIVE

• PRACTICAL

• ECONOMIC

To be economic, the design must be such as to maximize the bearing capacity of each pile while at the same time providing an adequate margin of safety against failure or excessive deformation of either individual piles or pile group.



WHY PILES SHOULD BE CHOSEN FOR A PARTICULAR CASE ?

• ENGINEERING REQUIREMENTS

• CONVENIENCE

• SPEED OF ACTION

OBJECTIVES

• EFFECTIVE

• PRACTICAL

• ECONOMIC



A pile foundation is a system acting as a composite constructionconsisting of three elements: footing, piles and subsoil

QTOTQTOT QTOT PS

n

1ii,pSTOT QQQQQ +=∑+=

=

load sharing coefficient, αpr

TOT

PG

TOT

n

1ii,pile

pr QQ

Q

Q=

∑=α =

αpr = 0 1 ]0,1[

S PG C

1

10

100

1 3 5FS,UR [-]

w [

cm]

B = Bopt

Not realistic Shallow foundations(pads, beams, rafts, …)

Deep foundations (piles)

FSUR > FSminwUR > wadm

SBD

FSUR < FSminwUR > wadm

CSBD



Whatever the case, the design process of a pile foundation always contains the following steps:

• Assessment of the behaviour of single pile, taking in a due account technological factors

• Evaluation of the interaction effects among piles (group effects), either when assessing displacement behaviour under working loads or when evaluating bearing capacity

• Consideration of the contribution of the pile cap (if the case)



PILE CLASSIFICATION

DISPLACEMENT PILESDISPLACEMENT PILES

NON DISPLACEMENT PILESNON DISPLACEMENT PILES

LARGE DISPLACEMENT SMALL DISPLACEMENT

BORED

CFA

INSTALLATION METHODINSTALLATION METHOD

OTHERS (barrette, micropiles)



0 0.4 0.8 1.2β = τslim/σ'v

Bored piles in sandD = 0.914 m L = 10 m

bentonite cake < 1 mm

polymer no cake

bentonite cake ≈ 10 mm

Ata e O’Neill (1997)

Installation effect on shaft resistance



Installation effect on shaft resistance

0 0.2 0.4 0.6 0.8 1α = τslim/Cu

Beaumont clay - OCR = 4÷10 - IP = 25÷55%D = 0.273÷0.914 m L = 7÷24 m

Bored - polymer

Bored - bentonite

Bored - dry

Closed-end steel pile

O’Neill (1999)



Poulos et al., 2001

It is very difficult to recommend any single approach as being the more appropriate for estimating axial bearing capacity of a single pile.



Mandolini et al., 2005

The most reasonable approach seems to be that of developing regional design methods (L5) combining the local experiences of both piling contractors and designers.The reliability of such methods depends on the quantity and quality of available evidence, particularly:

- detailed installation parameters- well-conducted and well-interpreted load tests




CONTINUOUS FLIGTH AUGER, CFA

Developed in The Netherlands, ’60sLarge use in Europe, not appreciated in USA (forbidden by FHWA)

0

20

40

60

80

100

1984 1985 1986 1987 1988 1989 1990 1991 1992

% of

pile

typ

e

non displ. pilesauger pilesdispl. piles

0

20

40

60

80

100

2000 2001 2002 2003 2004

Trevisani, 1992 Mandolini, 2004



ConcretePump





ConcretePump

PENETRATION STAGE

Rate of penetration, vPRate of revolution, ωP

Viggiani (1989, 1993)

Kinematic analysis: in order not to decompress surrounding soils:

VP > VP,CR = ωP⋅λ⋅[1-(d0/dN)2]

λ = pitch of the screwd0 = outer diameter of the central hollow stemdN = overall diameter of the auger

Mt

λ

d0

dNON DISPLACEMENT PILESNON DISPLACEMENT PILES




ConcretePump

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

do / d

vp /

(p

x )

terreno dislocato:vP > ωP x λ

terreno asportato:vP < ωP x λ



displaced soil:vP > ω x λ

removed soil:vP < ω x λ



ConcretePump

RETRIEVAL STAGE

Retrieval rate, vRωR = 0

Mandolini (2002)

In a given time ∆T:

VC = QC x ∆T∆s = VR x ∆T

Avg. pile diameter over ∆s:

d =VC/∆s = 1,13x(QC/VR)0,5





ConcretePump





The bearing capacity and settlement behaviour of CFA piles is toa large extent influenced by the equipment used and theexperience of the operator.

The significance of these two aspects is often underestimate oroverlooked at the design stage, but plays an important role forthe performance of CFA piles.

The use of a reliable system to monitor and record the wholeprocess of construction (auger depth z, , revolution w, penetrationrate VP, uplift rate VR, concrete supply QC, injection pressure PC)of this type of pile is therefore highly recommended.



two rectangularrafts

eight circularrafts

twobuildings

minorstructures

≈ 1500CFA piles

≈ 1300CFA piles

≈ 200CFA piles

≈ 300CFA piles

≈ 3300 piles (60% dN = 0,8 m; 40% dN = 0,6 m), L = 24 m

TOTAL LENGTH TOTAL LENGTH ≈≈ 80 km, TOTAL VOLUME 80 km, TOTAL VOLUME ≈≈ 33.000 m33.000 m33

Need of an accurate control during executionNeed of an accurate control during execution

The huge treatment plans in the plan of Sarno River



0

5

10

15

20

25

30

0.0 0.5 1.0CC [-]

dept

h [m

]

0

5

10

15

20

25

30

10 20 30 40ϕ [ ° ]

0

5

10

15

20

25

30

0 10 20 30qC [MPa]

Top soil

alluvialsoils

baseformation

Experimental site (Mandolini et al., 2002)

GWL

Subsoil investigations over an area of about 10000 m2:

• 7 bore-holes up to 50 m• 17 Cone Penetration Tests (CPT)• 7 Piezocone Tests (CPTU)• 4 Seismic Piezocone Tests (SCPTU)• 30 undisturbed samples for lab tests



STAGE I STAGE I -- Check of the monitoring systemCheck of the monitoring system

10 piles of reduced lengthwere installed, then extractedin order to measure overalllength and true diameter(step 0,5 m)



STAGE II STAGE II -- SLT on instrumented trial CFA pilesSLT on instrumented trial CFA piles

3 trial piles ( 2 piles dN = 0,8 m and 1 piles dN = 0,6 m) wereinstalled and instrumented alongthe shaft with the LCPCretrievable extensometer, thenloaded up to QMAX = 3 - 4 timesthe working load QW



STAGE III STAGE III -- Construction of the piled foundationsConstruction of the piled foundations

- For all the constructed piles,installation parameters havebeen recorded

- 9 proof tests on d = 0,8 mpiles have been performed

- 300 non destructive tests(20% of the number of piles)

CASAGRANDE C600



d = 0,8 mL = 24 m

d = 0,6 mL = 22,5 m

d = 0,8 mL = 24,1 m





0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80

settlement, w [mm]

load

[MN

]Results of loading tests on Results of loading tests on ddNN = 0,8 m CFA piles= 0,8 m CFA piles

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80

settlement, w [mm]

load

[MN

]

total loadshaft loadbase load

@1 - L = 24,0 m @3 - L = 24,1 m

QMAX = 4,08 MNSMAX = 2,81 MNPMAX = 1,55 MNwMAX = 75,6 mm

QMAX = 5,30 MNSMAX = 3,94 MNPMAX = 1,36 MNwMAX = 22,8 mm



Viggiani (1989): insertion of the auger

- in order not to decompress the surrounding soil:

VP > VP,CR = ω ⋅ λ ⋅ [1 - (d0 / dN)2]

ω = rate of revolutionλ = pitch of the screw (0,5 m and 0,6 m)d0 = outer diameter of the central hollow stem (0,18 m)dN = overall diameter of the auger (0,6 m and 0,8 m)

dN = 0,8 m ⇒ VP,CR (m/h) = 34,2 ⋅ ω (r.p.m.)

dN = 0,6 m ⇒ VP,CR (m/h) = 27,3 ⋅ ω (r.p.m.)



0 10 20

ω [r .p.m .]

0 250

500

V P [m /h]

0 10 20ω [r .p.m .]

0 250

500

V P [m /h]

0

10

20

30

0 10 20 30

q c [M Pa]d

ep

th [

m]

0

10

20

30

0 10 20 30

q c [M Pa]

de

pth

[m

]Pile @1

VP < VP,CRITalong all the shaft

“BORED” - ND PILES

Pile @3

VP ≈ VP,CRITalong almost all the shaft

“DRIVEN” - D PILES



Extraction of the auger

- time interval ∆t

Concrete volume VC = rate of flow QC x time interval ∆t

Upward displacement ∆ = retrieval rate VR x time interval ∆t

Average cross section AAV and pile diameter dAVover the distance ∆

AAV = QC / VR dAV = (4 ⋅ AAV / π )0,5 = 1,13 ⋅ (QC / VR )0,5



0

10

20

30

0 50 100

150

QC [m 3/h]d

ep

th [

m]

50 150

250

350

V R [m /h]

0.75

0.85

0.95

d [m ]

0

10

20

30

0 50 100

150

QC [m 3/h]

de

pth

[m

]

50 150

250

350

V R [m /h]0.

75

0.85

0.95

d [m ]

Pile @1dAV > dN

along the entire shaft

dS = 0,82 m; dB = 0,84 m

Pile @3dAV > dN

along the entire shaft

dS = 0,85 m; dB = 0,94 m



pile n° 2

pile n° 1pile n° 3

0,0

1,0

2,0

3,0

0 20 40 60 80

settlement, w [mm]

base

pre

ssur

e, p

[MPa

]

_____ corrected-------- uncorrected

pile n° 2

pile n° 1

pile n° 3

0

20

40

60

80

0 20 40 60 80

avg.

she

ar s

tress

, s [k

Pa]

_____ corrected-------- uncorrected



BackBack--Analysis: Design Parameters for StrengthAnalysis: Design Parameters for StrengthsMAX = k ⋅ µ ⋅ σ′V pMAX = Nq ⋅ σ′VL

orsMAX = αS ⋅ qC,S pMAX = αB ⋅ qC,B

µ = tan(Φ)qC,S = average value of qC up to L - 4 ⋅ dNqC,B = average value of qC between the depths ( L - 4 ⋅ dN) and ( L + dN)



sMAX = αS ⋅ qC,S

pMAX = αB ⋅ qC,B

0.02

0.03

0.04

0.0 1.0 2.0VP/VP,CR

α S

0.15

0.20

0.25

0.0 1.0 2.0VP/VP,CR

α B

αS = 0,026 x (VP/VP,CR) + 0,004 αB = 0,115 x (VP/VP,CR) + 0,153

BackBack--Analysis: Design Parameters for StrengthAnalysis: Design Parameters for Strength

BackBack--Analysis: Design Parameters for StiffnessAnalysis: Design Parameters for Stiffness

Randolph & Wroth (1978): Q/(w⋅r0⋅GL) = f (η, ξ, ζ, ρ, EP, L/r0)

From SCPTU: G [MPa] = 10 + 4⋅z [m]; GB = 330 MPa

G* = modified values atpile-soil interface

Assuming G*B/GB = aB

G*B/GB G*S/GS

@1 shaft base 0.180

0.320

@2 shaft base 0.246

0.420

@3 shaft base 0.184

0.420

Pile

0.20

0.40

0.60

0.0 1.0 2.0VP/VP,CR

G* S

/GS

G*S /GS = 0,274 x (VP/VP,CR) + 0,144



Procedure for the selection of piles to be testedProcedure for the selection of piles to be tested

0

5

10

15

20

25

30

0 10 20ω [r.p.m.]

dept

h [m

]

0

5

10

15

20

25

30

0 500

vP [m/h]

dept

h [m

] (VP / VP,CR ) ⇒ αS, G*S

0

5

10

15

20

25

30

0.7 0.8 0.9 1.0

d [m]

dept

h [m

]

SLIM = [π ⋅ dS ⋅ (L - 4 dS)] ⋅αS ⋅ qCS

PLIM = [0,25 ⋅π ⋅ dB2] ⋅ αB ⋅ qCB

(VP / VP,CR ) ⇒ αB, G*B

⇒ QLIM

(Randolph & Wroth, ‘78) ⇓

[QLIM /FS] /w = QW /w



Results of 9 proof loading tests on piles Results of 9 proof loading tests on piles belonging to foundationsbelonging to foundations

+ 40%

- 25%

0

200

400

600

800

1000

0 200 400 600 800 1000QW /w [kN/mm], measured

QW

/w [k

N/m

m],

pred

icte

d



@ Experimental findings have confirmed that the behaviour ofCFA piles is intermediate between that of D and ND piles

@ Such behaviour is strongly influenced by the installationprocedures, not only during the penetration stage but also during the extraction of the auger

@ Proper graduation of concrete pumping rates couldcompensate possible soil loosening in the penetration stage,improving the performance of the piles

@ A preliminary procedure has been proposed, with the aim of making available a rational approach to the selection of thepiles to be tested

Further systematic experiments are neededFurther systematic experiments are needed

COMMENTSCOMMENTS



SUN won a national competition for a research funding by ItalianGovernment (about 900.000 €)

Partner: Società Italiana Fondazioni S.p.A.

4 experimental sites (n.c. and o.c clayey; loose and dense sandy soils)

For each experimental site: detailed geotechnical investigations

5 load tests at failure on fully instrumented trial piles installed with a different set of installation parameters

different concrete mix



U

L

Due to hydration phenomenon of the concrete embedded in a “dry” ambient, the upper part of the pile will tend to shrink with respect to the soil. The latter will react with upward forces

Due to hydration phenomenon of the concrete embedded in a “wet” ambient, the lower part of the pile will tend to swell with respect to the soil. The latter will react with downward forces

Falconio & Mandolini (2003)



U

LB

AKi

Ki

-10

-5

0

5

10-0.02 -0.01 0.00 0.01 0.02

w

A

load



U

LB

AKi

Ki

-10

-5

0

5

10-0.02 -0.01 0.00 0.01 0.02

w

A

τlim,measured < τlim,true



U

LB

AKi

Ki

-10

-5

0

5

10-0.02 -0.01 0.00 0.01 0.02

w

A

B



U

LB

AKi

Ki

-10

-5

0

5

10-0.02 -0.01 0.00 0.01 0.02

w

A

B

τlim,measured > τlim,true



Influence of residual stresses locked into piles

-3 m

-10 m

-20 m-35 m

-300

-200

-100

0

100

200

300

0 10 20 30 40 50 60 70 80 90 100time after casting [days]

µε

Experimental data fromEastern Napoli’s area (CDN)

Instrumented pile sectionsbelow water level



37

55

55

55

d

Sec. 2

Sec. 1

Sec. 3

Sec. 4

Sec. 5

Sec. 6

Sec. 7

Sec. 842

102

139

p.l.f.

γsat=1,1 - 1,4 t/mc; qc=2,5 MPa

γsat=1,6 - 1,8 t/mc; qc=15 MPa

qc=5 MPa

γsat=1,5 - 1,6 t/mc; qc=10 MPac'=0; φ=36°-40°

γsat=1,5 - 1,6 t/mc; qc=20 MPac'=1 -2 kg/cmq; φ=28°-32°

Sand

Loose pozzolana

Weakly cemented pozzolana

Peat

Riporto

d

Piles A - C d=1,5mPiles B - D d=2,00

0,0

5,0

10,0

15,0

20,0

25,0

30,0

35,0

40,0

-150 50 250µε

z [m

]

SRM

(a)

Experimental data from Eastern Napoli’s area (CDN)



EXPERIMENTAL DATA FOR CAST IN SITU BORED PILES



Two additional possible explanations:

a) Influence of soil stress history at small depths

b) Influence of dilatancy



COMMENTSCOMMENTS-Similarly to what happens for different phenomena like downdrag, the initial distribution of residual stresses along the pile affects the distribution of the shaft friction at the end of the load test;

-Being the load resultant at the beginning of the test equal to zero (no load at the pile head), no appreciable differences have to be expected in terms of ultimate capacity;

-Numerical studies and available case histories highlight the errors commonly made when interpreting the results of loading tests on instrumented piles assuming a stress-free pile;

-As for driven piles, it is not rational to neglect residual stresses when dealing with cast in situ bored piles;

-Part of the large scattering of experimental β values have to be attributed to these effects.



Mandolini et al., 2005

The most reasonable approach seems to be that of developing regional design methods (L5) combining the local experiences of both piling contractors and designers.The reliability of such methods depends on the quantity and quality of available evidence, particularly:

- detailed installation parameters- well-conducted and well-interpreted load tests



Type of load tests

Poulos, 2000; Randolph, 2003



test pile

a) ideal test

fixed point

level

load

An ideal load test on pile is that applying to the ground a load system with non-zero resultant



Kentledge

Before the start of the load test, the weight of the kentledgeis transmitted to the supporting soil at the surface.It follows that the state of stress into the soil will be altered, then allowing for a different response of the embedded pile.

Tension piles or anchors

During the loading stages, reaction piles will be loaded in opposite direction, altering the shear stresses at soil-pile interface.




Q -Q/2-Q/2Simplified formula (Fleming et al., 1992):

αij = 1 – ln(sij/ro)/ζ; ζ = ln(rm/ro)



0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40si,j/r0 [-]

inte

ract

ion

fact

or, α

i,j [-

] GL/GB=1GL/GB=1/3

Homogeneous soil

ρ=GL/2/GL=0,67; νs=0,5L/ro=50, λ=EP/GL=1000


Q -Q/2-Q/2



0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40si,j/r0 [-]

inte

ract

ion

fact

or, α

i,j [-

] GL/GB=1GL/GB=1/3

6 < s/ro < 14GL/GB = 1/3 → 0,15 < αij < 0,42GL/GB = 1 → 0,29 < αij < 0,52


Q -Q/2-Q/2



0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40si,j/r0 [-]

inte

ract

ion

fact

or, α

i,j [-

] GL/GB=1GL/GB=1/3

GL/GB = 1/3 → w = (0,58-0,85)w↓

GL/GB = 1 → w = (0,48-0,71)w↓


Q -Q/2-Q/2

( )α−=×α−=+= ↓↑↓ 1w2QI2QIwww ww



TP

ILTww

EE =

wILT = settlement during ILTwTP = settlement during TP

End-bearing piles (GL/GB = 1/3)at large distance (s/ro = 14)

Floating piles (GL/GB = 1)at small distance (s/ro = 6)

1,18 ≤ EE ≤ 2,08


Q -Q/2-Q/2



Osterberg Cell

Advantages

- More similar to ILT- No need for reaction system

Disadvantages

- Different loading condition (loaded at depth and down-top)- Interpretation depending on the hypotheses



Osterberg Cell

Supper

Slower

B

The O-Cell should be placed along the pile shaft at a depth for which the upper shaft load (Supper) is similar to the sum of the lower shaft load and of the base (Slower + B):

Qupper = Supper; Qlower = Slower + B



Osterberg Cell

Supper

Slower

B

If failure occurs for an upward movement of the pile head:

Qult > 2 x Qupper = 2 x Supper

If failure occurs for a downward movement of the lower part of the pile:

Qult > 2 x Qlower = 2 x (Slower + B)

If O-cell is placed at the base, Slower = 0 ⇒ Qupper = S; Qlower = BIt follows that two separate curves (shaft and base) can be obtained



Osterberg Cell

Supper

Slower

B

In the figure, B < S ⇒ Qult > 2 x B



Osterberg Cell

Supper

Slower

B

Hypotheses

a) The pile is rigid

b) The load-settlement relationship for shaft resistance is independent of the direction of the relative soil-pile movement

c) The stress and strain fields at the pile base and along the pile shaft are independent each other and the load-settlement relationships of the base and the shaft can be considered separately



Osterberg CellKentledge Tension piles or anchors

COMMENT

Whatever the type, load test setup affects the measured results !!



Numerical analysis by ABAQUS 6.2 for different load test setup(Recinto, 2004; Mandolini et al., 2005)

kentledge

jack

jack

spreader beam

Osterberg load cell

support

test pile

test pile

test pile

test pile

reactionpile

a) ideal test

c) reaction piles ground anchors

c)Osterberg cell

anchor

fixed point

level

test piletell

tales

load

b) test with kentledge

d) Osterberg ll

jack



= 3

1°

= 2

3°

= 2

7°

= 3

5°

0

20

40

60

80

100

0 2000 4000 6000 8000Q [kN]

w [

mm

] ILT

COLTtp

ILT

L/d = 20

s/d = 6

Tension piles Kentledge Osterberg

The ultimate load is not influenced by the load test setup

=31°

=23°

=27°

=35°

0

20

40

60

80

100

0 2000 4000 6000 8000Q [kN]

w [

mm

]

ILT

L/d = 20

= 3

1°

= 2

3°

= 2

7°

= 3

5°

0

20

40

60

80

100

0 2000 4000 6000Q [kN]

w [

mm

] ILT

L/d = 20




= 3

1°

= 2

3°

= 2

7°

= 3

5°

0

20

40

60

80

100

0 2000 4000 6000 8000Q [kN]

w [

mm

] ILT

COLTtp

ILT

L/d = 20

s/d = 6

=31°

=23°

=27°

=35°

0

20

40

60

80

100

0 2000 4000 6000 8000Q [kN]

w [

mm

]

ILT

L/d = 20

= 3

1°

= 2

3°

= 2

7°

= 3

5°

0

20

40

60

80

100

0 2000 4000 6000Q [kN]

w [

mm

] ILT

L/d = 20

Tension piles Kentledge Osterberg

The axial stiffness is strongly influenced by the load test setup




tension piles

kentledge

OCT

0

50

100

150

200

0 10 20 30 40 50L/d

k (%

)

f rictional material

tension piles

kentledge

OCT

0

50

100

150

200

0 10 20 30 40 50L/d

k (%

)

cohesive material

( )ILT

ILTK

KKk −=


Substantial overestimation of the axial stiffnessThe key factor is the pile slenderness L/d



Commercial Centre in Napoli – Bored pile d = 0,9 m; L = 22 m

Case history by Mandolini & Ramondini, 1998







STAGE IPreparation of the kentledge Q ∼ 11,5 MN

Average settlement of the kentledge 6,6 mm

Settlement of the unloaded pile 1,55 mm

INTERACTION EXISTS !!

zavorra

palo

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12

load on the foundation of the kentledge [MN]

disp

lace

men

t [m

m]



pile

kentledge



STAGE IILoading on pile up to Q ∼ 10 MN and unloading

Pile head settlement 9,8 mm (at the end of the test, residual 1,4 mm)

Upward movements of kentledge 1,9 mm (at the end of the test, residual 0,1 mm)

palo

zavorra

-4

-2

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12

load [MN]

disp

lace

men

t [m

m]



pile

kentledge



zavorra

palo

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12

load on the foundation of the kentledge [MN]

disp

lace

men

t [m

m]

Interpretation neglecting interaction

K0 = [dQ/dw]0 = 1,28 MN/mm

Interpretation considering interaction

K0 = [dQ/dw]0 = 1,06 MN/mm

“SOFTER” PILE (≈ 20%)



pile

kentledge



COMMENTSCOMMENTS

- Load test to failure is the most reliable design method of a pile

- Whatever the load test type adopted, the results must be interpreted looking at the entire system as made by elements interacting each other

- Although new load test setups have been recently proposed (OC),static load tests with kentledge or reaction piles give less affected results

- Due to increasing use of design methods based on stiffness consideration rather than capacity demand, a correct evaluation of the results of load tests is becoming increasingly crucial



Struttura del corsoStruttura del corso

VERIFICA FINALELezione 11Ottimo progettuale

Lezione 10Carico limite di piastre su pali

Giovedì06.03.08

Esercitazione 3Piastre su pali in condizioni di esercizio

Lezione 9Criteri innovativi di progettazione

Lezione 8Comportamento di pali in gruppo

Giovedì28.02.08

Esercitazione 2Pali soggetti a carichi trasversali



Giovedì21.02.08

Esercitazione 1Fondazioni soggette a carichi verticali

Lezione 5Pali soggetti a carico assiale


Giovedì14.02.08


Lezione 2Quadro normativo di riferimento

Lezione 1Criteri generali di progettazione

Giovedì07.02.08

15.00 – 17.3012.30 – 13.3010.30 – 12.00

ANALISI E PROGETTAZIONE DELLE FONDAZIONIANALISI E PROGETTAZIONE DELLE FONDAZIONI

Università degli Studi di Napoli Federico IISeconda Università degli Studi di NapoliUniversità degli Studi di SalernoUniversità degli Studi di Napoli ParthenopeUniversità degli Studi del Sannio

Università degli Studi Roma La Sapienza

Dottorato di Ricerca in Ingegneria Geotecnica

Documents

ANALISI E PROGETTAZIONE DELLE FONDAZIONIadpaloha.altervista.org/wp-content/uploads/2012/11/PDF_0607.pdf · Fondazioni superficiali (1) Lezione 2 Quadro normativo di riferimento Lezione