from piles to piled raft foundation

From Piles to Piled Raft Foundation - Some Observations on Static and Dynamic Analyses

Der-Wen Chang

Department of Civil Engineering

Tamkang University

Tamsui, New Taipei City, Taiwan 25137

E-mail: [email protected]

Department of Construction Engineering

National Kaohsiung First University of Science and Technology

Kaohsiung, Taiwan, April 21, 2016

Why Deep Foundation?

Mega-size/high-rise/heavy-load building on soft soils;

Large lateral and overturning loads;

Large fdt. settlement and differential settlements;

Seismic threats and soil liquefaction induced fdt.

damages.

2

Types of Deep Foundations

Piles and Piers;

Combined Pile Raft Foundation (CPRF);

Caisson;

Barrette (Buttress pile/wall) and Grid Walls.

3

Offshore foundations

1. Soil-Structure-Fluid Interactions must be considered

2. Cyclic loading effects (both static and dynamic) are significant

4

5

M

f / fm

1.0

1.0

0.5fm< f <2fm

Stiffness controlled

Dynamics controlled

Mass controlled

Effects of the steady-state loads

Rotational frequency

and Blade Passing frequency

must be avoided

6

P

U

Degradation of fdt. Resistance under cyclic loads

˝+˝ direction

˝-˝ direction

K2

K1

K1 > K2； 1 < 2

Outlines

1. Design procedures and analyses (5)

2. Simplified analysis for seismic behaviors of piles (10)

3. Applications of dynamic pile-to-pile interaction

factors (5)

4. Seismic performance of piles – PBEE approach (11)

5. Seismic performance of piles – RB approach (6)

6. Design and analyses on CPRF (4)

7. Simplified analysis for seismic behaviors of CPRF (9)

8. Foundation behaviors from analyses (17)

9. Concluding remarks (6)

7

I. Design procedures

and analyses

8

1. Ultimate Limit State –

External/Internal

Foundation Capacities

2. Serviceability Limit State –

External/Internal

Foundation Serviceability

Geotechnical Engineering

Design

Performance-Based

Design

Reliability-Based methods,

Propability-Based methods,

Load and Resistance Factor

Design.

Working Stress Design,

Limite State Design

Conventional

Design

Uncertainties of the design must

be analyzed systematically

RBM: FORM, FOSM, Monte Carol

Simulation, etc.

PBM: PBEE analysis

LRFD: AASHTO

9

Probability-Based methods

Design Flow Chart for Pile Fdt.

開始

資料蒐集

選擇基樁形式及材料

基樁材料容許應力計算

基樁容許支承力計算

決定基樁數目

基樁配置

合適

基樁沈陷量計算

沈陷量檢核

允許

表面負摩擦力

有

負摩擦力計算

樁支承力

安全

地層狀況、土壤強度性質、設計荷重情形、施工狀況調查

包含使用材料、形狀大小、長度，施工方法等之假定

否

過量

否

無

是否高液化潛能之地盤地盤改良

否

是

安全

水平力作用

利用直樁

是

計算基樁水平支承力

水平承載樁數檢核

承受拉力

基樁容許拉力計算

承受拉力樁數檢核

是

樁帽設計

樁基設計圖

完成

足夠

計算斜樁數目及排列

否

無

否

不足

無安全

10

Concerns

1. Vertical capacity of single pile;

2. Lateral capacity of single pile;

3. Negative skin friction of single pile;

4. Pull-out resistance of single pile;

5. Liquefaction effects on single pile and grouped piles;

6. Settlement and lateral deflections of single pile;

7. Effects of pile-to-pile interactions on grouped piles;

8. Pile cap design and safety checks on piles and cap.

Problems require further attentions

1. Statically cyclic loads (effects of unload/reload and number of cycles);

2. Dynamically cyclic load (effects of amplitude/period and initial static load);

3. Seismic loading (PGA/duration/dynamic characteristics);

4. Capacities of Piled Raft foundation (external and internal);

5. Serviceability of Piled Raft foundation (external and internal).

11

On PBD and PBSD

Ground conditions,

Soil properties parameters,

Loads/Displacements of the structure,

Measurements and calculation methods,

Site construction methods

Performance-Based Design

Foundation Capacities Foundation Deformations

Uncertainties

Reliability-Based methods─FOSM, FORM, MCS,

Probability-Based methods─PBEE,

LRFD method, Fuzzy Logic, Evidence Theory…etc.

PBSD of pile fdt

Physical Tests Numerical Modeling

FEM analysis,

FDM analysis,

BDWF modeling,

Wave equation modeling

In-situ full scale pile load test,

Shake table test,

Centrifuge test,

Push-over model test

Method Factor of safety against seismicity

Medium

earthquake

Design

earthquake MCE

PBEE

analysis Mcr / Mmax My / Mmax Mult / Mmax

Monte Carlo

Simulation cal /R cal /R cal /R

Note: Mcr = moment when concrete crack starts; My = moment when

steel bar yields; Mult = moment when plastic hinge occurs;

Mmax = calculated maximum bending moment; cal =

calculated reliability index; R = required reliability index

12

PBSD

Concerns

Conventional Design

Seismic Design

in options (need to

consider soil

liquefaction effects)

Foundation Capacities

Fdt. Deformations

Deterministic approach

and/or Probability approach ?

Pile Design

Determine V、H、D、L、Ar

Conventional Design

(Ordinary、Critical)

Seismic PBD ?

PGAt from hazard carve

Seismic record in use

Calibrate a(t) for analysis

Use LPIPE to compute

Mcr、My、Mult

Choose proper tool

Calibrate the model

parameters

Find Umax、Mmax

Apply PBEE to find

λvsUmax and λvsMmax

Use Mcr、My and Mult to find

Umc、Umy、Umm

Based on seismic design level

Compare Umax with Umc/Umy/Umm

Check Umax<Umc/Umy/Umm

End of Design

Redesign

YES

NO

OK

NG

Compare Mmax

with Mcr/My/Mult

OK NG

Optional

13

PBEE

approach

II. Simplified analysis for

seismic behaviors of piles

14

EQWEAP (EarthQuake Wave Equation Analysis for

Piles)

Seismic pile responses Seismic Free-Field

Response by LMA

Seismic Pile

Response by WEA

Decoupled motions + Uncoupled analysis

15

16

WEAP under EQ excitations

2

2( )

uA x

t

( , )P x t

MM

x

xP

xP

VV

x

x

M

V

( )M t( )M t

xPxP

)t(Q

)t(Q

sC

sK

Discrete pile segments and equilibriums

EQWEAP Formulas

1. If ground motions were obtained from free-field analysis

2. If seismic earth pressures were given

3. If ground displacement profiles were prescribed

17

Chang et al. (2014)

EQWEAP Formulas (cont.)

1. For ground motions from free-field analysis:

2. For seismic earth pressures already known:

3. For ground displacement profiles already known:

18

19

Pile Nonlinearity

Iterative analysis is conducted to modify the EI values according

to M- relationship

1 yM E I M Z Approximate Bouc-Wen Model :

I

II

III

0.0E+0 4.0E-3 8.0E-3 1.2E-2 1.6E-2

Curvature (rad/m)

0

5000

10000

15000

20000

Mom

ent

(kN

-m)

Percentage of Steel = 1.94 %

Diameter of Pile = 0.5 m

Diameter of Pile = 1 m

Diameter of Pile = 2 m

Mu ,ψu

0.0E+0 4.0E-3 8.0E-3 1.2E-2

Curvature (rad/m)

0

1000

2000

3000

4000

Mom

ent

(kN

-m)

Diameter of Pile = 1m




Mu ,ψu

Effects of Pile Diameter and Ar

on Moment Capacities of pile

20

Pile displacement at different time step

from SPRC model Pile displacement at different time step

from EPWP model

-40 0 40 80

Pile Displacements (cm)

0

6

12

18

24

30

36

De

pth

(c

m)

Liquefiable Layer

Soil Parameter Reduction Coefficient

Failure occurred at 7 sec

Time at 15 sec

Time at 25 sec

Time at 35 sec

-40 0 40 80


0

6

12

18

24

30

36D

ep

th (

cm

)

Liquefiable Layer

PWP Model


Time at 15 sec

Time at 25 sec

Time at 35 sec

21

-160 -80 0 80 160


0

6

12

18

24

30

36

De

pth

(c

m)

Liquefiable Layer

Direct Earth Pressure


Time at 15 sec

Time at 25 sec

Time at 35 sec

-100 -50 0 50 100


0

6

12

18

24

30

36D

ep

th (

cm

)

Liquefiable Layer

Indirect Earth Pressure


Time at 15 sec

Time at 25 sec

Time at 35 sec

Pile displacement at different time step

from direct earth pressure model Pile displacement at different time step

from indirect earth pressure model

22

-40 0 40 80


0

6

12

18

24

30

36

Dept

h (c

m)

Liquefiable Layer

Observed (No. 9)

Observed (No. 2)

Predicted (Ishihara and Cubrinovski, 2004)

Direct Earth Pressure Model (failure occurred at 4.4 sec)

Indirect Earth Pressure Model (failure occurred at 5.4 sec)

PWP Model (failure occurred at 7.0 sec)

Soil Parameter Reduction Coefficient (failure occurred at 7.0 sec)

Maximum pile displacement profiles from alternate

modeling of EQWEAP analysis and the field observations 23

Grouped Piles

24

III. Applications of Dynamic

pile-to-pile interaction factors

25

Dynamic pile-to-pile interaction factor

Dobry and Gazetas (1988)

26

Pile-to-Pile Interactions

27

Use of superposition theory

28

Lateral

load

distributions (Chang et al, 2009)

29

Load ratio

varied at

frequencies

and the

time-

dependent

history (Chang et al.

2009)

30

IV. Seismic performance of

piles – PBEE approach

31

32

Performance Safety Serviceability Rehabilitation

Short term Long term

Level I structure remained

elastic same as before not needed

routine monitoring,

protections

Level II

restricted local

damages,

recoverable

recoverable w/ short-

term remedies

urgent remedy method

applicable

existing remedy method

applicable

Level III

superstructure and main

body collapse

prohibited

urgent remedies

applicable,

limited

speed/weight

for vehicles

Replacing elements,

structural

reinforcements

undertaken

closed for

constructions

Hazard Level Embankment

Bridge pile foundation Underground structures

ordinary important ordinary important

S30 Level I Level I Level I

S475 Level III Level III Level II Level III Level II

S2500 N/A N/A Level III N/A Level III

Seismic Performance Concerns for Transportation Structures (after Chen et al., 2006)

Seismic Performances and Return Periods for Transportation Structures (after Chen et al., 2006)

Seismic Performance Requirements

33

Local seismic hazard curve

City＼TR

PGA (g)

30 yr

TR1

475 yrs

TR2

2500 yrs

TR3

Taipei 0.12 0.29 0.51

Hsinchu 0.12 0.38 0.60

Taichung 0.14 0.60 0.94

Chiayi 0.20 0.59 0.83

Tainan 0.16 0.51 0.75

Kaoshiung 0.12 0.35 0.54

Pingtung 0.15 0.41 0.60

I-lan 0.20 0.45 0.63

Hualian 0.21 0.60 0.81

Taitung 0.21 0.57 0.85 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Intensity Measures, PGA(g)

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

Ann

ual P

roba

bilit

y of

Exc

eeda

nce(

1/ye

ar) 台北市

新竹市

台中市

嘉義市

台南市

高雄市

恆春鎮

宜蘭市

花蓮市

台東市

30yr

475yr

2500yr

Taipei

Cheng (2002)

If Seismic Design Code is followed, PGAt are 0.06g, 0.24g and 0.32g in

Taipei

Kaohsiung

Taichung

34

Total probability P for the occurrence of a event can be computed as an integral of all the probabilities that could occur.

For the occurrence of consecutive scenarios such as a, b and c, the total probability of occurrence P can be computed as

Probability Method - PBEE Analysis

0.4 0.2 0.6

P = 0.6*0.4*0.2 = 0.048

PBEE (Performance Based

Earthquake Engineering) Analysis

A probability based approach suggested by US PEER

Excellent summary can be found in Kramer (2008)

DM EDP IMN N N

k k jDV

k 1 j 1 i 1

j i IM i

DV P DV dv DM dm P DM > dm EDP edp

P EDP edp IM im im

: Annual Rate (probability) of Exceedance

DV: Decision Variable (costs of the hazard) DM: Damage Measure (maximum bending moment)

EDP: Engineering Demand Variable (maximum pile displacement)

IM: Intensity Measure (mostly used - PGA)

35

KEY - Seismic Hazard Curve

λ=ΣΣΣυP[ IM>im| M =m, R= r] P[M =m] P[R= r]

k

im 0k IM

36

37

Demand curve

Fragility curve

38

-k1/b 2 2

EDP 0 0 2

EDP k EDP, a, b, k, k , k exp

2f

a b

0.0 0.2 0.4 0.6PGA, IM (g)

0

40

80

120

Dis

pla

ce

me

nt,

ED

P (

cm

)

PGA=0.12g

PGA=0.29g

PGA=0.51g

0 40 80 120Displacement, EDP (cm)

1E-4

1E-3

1E-2

1E-1

1E+0

An

nu

al

Pro

ba

bil

ity

of

Ex

ce

ed

an

ce

(1

/ye

ar)

EDP vs IM vs EDP

39

-k1 b

2d2 2 2

DM 0 R D2 2

1 k( ) k exp d

a c 2b d

DMDM

0 40 80 120Maximum Displacement (cm)

0

100

200

300

400

Ma

xim

um

Mo

me

nt

(10

^2

kN

-m)

PGA=0.12g

PGA=0.29g

PGA=0.51g

0 200 400 600Maximum Moment (10^2kN-m)

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

An

nu

al

Pro

ba

bil

ity

of

Ex

ce

ed

an

ce

(1

/ye

ar)

DM vs EDP vs DM


1E-4

1E-3

1E-2

1E-1

1E+0

An

nu

al

Pro

ba

bil

ity

of

Ex

ce

ed

an

ce

(1

/ye

ar)

21 49 84

18 45 79

PBEE Analysis I

Annual rate of exceedance vs. Max. pile displacements at various EQ levels


1E-4

1E-3

1E-2

1E-1

1E+0

An

nu

al

Pro

bab

ilit

y o

f E

xce

ed

an

ce

(1

/ye

ar)

40

PBD Findings II (Mcr= 7300 kN-m, My= 22100 kN-m, Mult= 29700 kN-m)


1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

An

nu

al

Pro

ba

bil

ity

of

Ex

ce

ed

an

ce

(1

/ye

ar)

180 100 240 190

270 260


1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

An

nu

al

Pro

ba

bil

ity

of

Ex

ce

ed

an

ce

(1

/ye

ar)

Annual rate exceedance vs. Maximum pile moment at various EQ levels

NG

OK

OK

OK

OK

NG

41

From the moment capacities to find

the design probabilities , then use

to determine allowable pile

displacements, Umc, Umy and Mmm

Ductility Index, R =1.5

Alternative Procedure

42

V. Seismic performance of

piles – Reliability approach

43

Reliability Approach - MCSM

Probability of failure Pf = nf/ntotal

Assuming normal distribution or log-normal

distribution, reliability index can be

computed from mean value m and standard

deviation of the scenarios.

Variability of seismic records, soil parameters

and the geological conditions could be

considered.

It was found that the seismic input is

especially significant to the results.

44

45

Monte Carlo Simulation based on

Weighted PGA

For PGAt, compute all the scenarios including variability of soil parameters and all possible seismic intensities PGAi PGAt.

The seismic records for the acceleration time history of the site can be achieved using specific methods.

Then, Pft at PGAi PGAt = Pfi Wi Total probability of failure, Pft represents for the total potential influences of all possible EQs under the design EQ level is suggested.

Calculating the weights

PGA

I

II III

Design Life = 50 years

1- = cumulated

probability of EQ PGAt

( )( ) ( ) (1 ( ) ) A

A A A

dR ad dP a F a R a

da da da

46

Weighted Intensities (Chang et al, 2014)

PGA (g)

Return period (year)

(%)

Probability of occurrence for

a > PGA

Probability of occurrence for

a PGA

Numerator of the central difference

formula Weights

0.01 1 100.00 1.0 0.000 5.00E-03 2.50E-03

0.02 1.005 99.50 0.995 0.005 1.00E-02 5.00E-03

0.03 1.01 99.00 0.99 0.010 4.95E-01 2.48E-01

0.04 2 50.00 0.50 0.500 7.50E-01 3.75E-01

0.05 4 25.00 0.250 0.750 3.33E-01 1.67E-01

0.06 6 16.67 0.167 0.833 1.25E-01 6.25E-02

0.07 8 12.50 0.125 0.875 6.67E-02 3.33E-02

0.08 10 10.00 0.100 0.900 5.36E-02 2.68E-02

0.09 14 7.14 0.071 0.929 5.00E-02 2.50E-02

0.10 20 5.00 0.050 0.950 2.98E-02 1.49E-02

0.11 24 4.17 0.042 0.958 1.67E-02 8.33E-03

0.12 30 3.33 0.033 0.967 1.31E-02 6.55E-03

0.13 35 2.86 0.029 0.971 9.52E-03 4.76E-03

0.14 42 2.38 0.024 0.976 8.57E-03 4.29E-03

0.15 50 2.00 0.020 0.980 7.42E-03 3.71E-03

0.16 61 1.60 0.016 0.984 6.11E-03 3.06E-03

0.17 72 1.40 0.014 0.986 5.03E-03 2.51E-03

0.18 88 1.14 0.0114 0.9886 3.89E-03 1.94E-03

0.19 100 1.00 0.0100 0.990 3.36E-03 1.68E-03

0.20 125 0.80 0.0080 0.992 3.01E-03 1.50E-03

0.21 143 0.70 0.0070 0.993 1.90E-03 9.51E-04

0.22 164 0.61 0.0061 0.9939 1.73E-03 8.65E-04

0.23 190 0.53 0.0053 0.9947 1.57E-03 7.86E-04

0.24 221 0.45 0.0045 0.9955 1.29E-03 6.47E-04

0.25 252 0.40 0.0040 0.996 1.03E-03 5.14E-04

47

Weighted intensities (continued)

0.26 286 0.35 0.0035 0.9965 9.65E-04 4.83E-04

0.27 333 0.30 0.003 0.997 9.33E-04 4.66E-04

0.28 390 0.26 0.0026 0.9974 8.98E-04 4.49E-04

0.29 475 0.21 0.0021 0.9979 5.64E-04 2.82E-04

0.30 500 0.20 0.002 0.998 2.30E-04 1.15E-04

0.31 533 0.19 0.0019 0.9981 2.61E-04 1.30E-04

0.32 575 0.17 0.0017 0.9983 2.50E-04 1.25E-04

0.33 615 0.16 0.0016 0.9984 3.19E-04 1.59E-04

0.34 704 0.14 0.0014 0.9986 3.75E-04 1.87E-04

0.35 800 0.13 0.0013 0.9987 2.80E-04 1.40E-04

0.36 877 0.11 0.0011 0.9989 2.50E-04 1.25E-04

0.37 1000 0.10 0.0010 0.999 2.05E-04 1.02E-04

0.38 1069 0.09 0.0009 0.9991 1.43E-04 7.15E-05

0.39 1167 0.09 0.0009 0.9991 1.35E-04 6.77E-05

0.40 1250 0.08 0.0008 0.9992 1.29E-04 6.43E-05

0.41 1373 0.07 0.0007 0.9993 1.21E-04 6.05E-05

0.42 1473 0.07 0.0007 0.9993 1.17E-04 5.84E-05

0.43 1635 0.06 0.0006 0.9994 1.13E-04 5.66E-05

0.44 1767 0.06 0.0006 0.9994 9.16E-05 4.58E-05

0.45 1923 0.05 0.0005 0.9995 7.35E-05 3.68E-05

0.46 2031 0.05 0.0005 0.9995 5.85E-05 2.92E-05

0.47 2167 0.05 0.0005 0.9995 5.78E-05 2.89E-05

0.48 2301 0.04 0.0004 0.9996 5.39E-05 2.69E-05

0.49 2453 0.04 0.0004 0.9996 3.04E-05 1.52E-05

0.50 2475 0.04 0.0004 0.9996 7.69E-06 3.84E-06

0.51 2500 0.04 0.0004 0.9996 4.79E-05 2.39E-05

48

Factor of Safety (Chang et al., 2014)

Method

Factor of safety, FP and FR

Moderate EQ

Design EQ

MCE quakes

PBEE

Mcr/Mmax

My/Mmax

Mult/Mmax

MCSM

obt./R

obt./R

obt./R

49

Whitman (1984) R = 2.4 for foundations

VI. Design and analyses

on CPRF

50

ISSMGE TC212 CPRF Guidelines

51

Load carried by the piles

The

optimized

design

0.5

52

Numerical modeling for Capacities

and Serviceability

Pult: ultimate load

Pall: allowable load

uall: allowable displacement

P

Pult

u

soft soils

stiff soils

Pall

Pall

uall

1. Ultimate capacity of the foundation could be estimated from

Load-displacement relationship of the foundation.

2. Displacements (or deformations) are controlled to avoid

the Structural damages.

3. Blind guess of the FS is not required.

53

3D FEM analysis as the tool

Examinations of numerical model, material

model, material parameters, loads, environment

and construction procedures

54

VII. Simplified analysis for

seismic responses of CPRF

55

Analyses for Piled Raft Fdt.

Matsumoto (2013)

1. Simplified calculation methods (Poulos-Davis-

Randolph)

2. Approximate computer-based methods

3. Rigorous computer-based methods

56

Poulos (2001)

Simplified modeling for seismic

responses of raft fdt.

Uncoupled motions of the slab

x

z y

Subjected to horizontal seismic motion

Underneath

Impedances

57

Motions of equivalent pier

equivalent

pier pile-soil-pile

elements

58

Analytical/discrete equations

𝐸𝐴𝜕2𝑢

𝜕𝑥2𝑑𝑥 = 𝜌𝐴𝑑𝑥

𝜕2𝑢

𝜕𝑡2+ 𝑘𝑠𝑏(𝑢 − 𝑢𝑔) + 𝑘𝑒𝑝 𝑢 − 𝑢𝑒𝑝 + 𝑘𝑠𝑡 1 − 𝑅 𝑢 + 𝑚𝑠𝑡𝑅

𝜕2𝑢

𝜕𝑡2

𝑢 𝑖, 𝑗 + 1

= 2𝐹 − 2 − 𝐵 − 𝐶 + 𝐷 − 𝐻

𝐹𝑢 𝑖, 𝑗 +

1

𝐹𝑢 𝑖 + 1, 𝑗

+1

𝐹𝑢 𝑖 − 1, 𝑗 − 𝑢 𝑖, 𝑗 − 1 +

𝐶

𝐹𝑢𝑒𝑝 𝑖, 𝑗 +

𝐵

𝐹𝑢𝑔(𝑖, 𝑗)

where 𝐹 =𝜌∆𝑥2

𝐸 ∆𝑡2 +𝑚𝑠𝑡𝑅∆𝑥

𝐸𝐴 ∆𝑡2 ; 𝐵 =𝑘𝑠𝑏∆𝑥

𝐸𝐴; 𝐶 =

𝑘𝑒𝑝∆𝑥

𝐸𝐴; 𝐷 =

𝑘𝑠𝑡∆𝑥𝑅

𝐸𝐴; 𝐻 =

𝑘𝑠𝑡∆𝑥

𝐸𝐴; x = spatial increment in x direction; t = time increment.

59

Numerical example – strip fdt. on piles

plan view

60m

60m

300m

60m

equivalent

pier

Seismic

direction

60m 60m 60m 60m 30m 30m

60

Seismic input

(a)(a) (a) (c)

(b) (d)

3D FEM Modeling

(a) (b)

(c) 61

Comparisons and Observations

(a) (b)

b)

-112cm

-102cm

108cm

102cm

62

Influences of bevel angle

z

y

Underneath

Impedances

63

Time efficiency

Method Computer features Computation time (sec)

EQPR analysis

CPU: Intel Xeon

E3-1231v3 RAM: 16GB

60 sec

based on time increments of

0.0005 sec (computations required for

EQWEAP analysis is

included)

3D Midas-

GTS analysis

9hr 25min 10sec

for 174780 elements based on time increments of

0.02 sec

64

VIII. Foundation behaviors

from analyses

65

Load distributions of piles

Study on spread raft on piles

66

27m

23m

v and h affected by loads and S/D

Sand-clay-sand model is used in monitoring

67

5 5-

Vertical displacements of raft

68

long-term

short-term

long-term

w/ consolidation

Stage load

w/o consolidation

Horizontal displacements of raft

69

long-term

short-term

Consolidation

Axial loads of piles

70

Consolidation

Skin frictions of piles

71

t-z and Q-z curves

72

Center Edge

Corner Corner

Edge

Center

Lateral resistances along pile shafts

Consolidation Stage loading (drained) Stage loading (undrained)

73

p-y curves

74

Center Side edge

Rear corner

Front edge

Front corner

Study on

physical

model data (Unsever et al., 2014)

Vertical loading

Horizontal loading

75

Axial

forces

Moments Shears

76

Behaviors of piled raft foundation

77

Comparisons on Midas and

EQWEAP analyses

78

PBEE analysis from EQWEAP

OK

OK

NG

79

Behaviors of ring-shaped grouped piles

80

Comparisons on Midas and

EQWEAP analyses

81

PBEE analysis from EQWEAP

OK

OK

OK

82

VIIII. Concluding Remarks

83

On methodologies

1. Accuracy of the pile analysis and design relies on the knowledge of site soils.

2. The load effects need further investigations.

3. PBD and PBSD became more important to design practice of deep foundation.

4. Unless the uncertainties of design parameters are considered, the analysis in monitoring the foundation behaviors ≠ performance-based analysis.

5. Load-displacement relationships of the fdt. should be analyzed using 3D FEM analysis. Both capacities and serviceability of CPRF could be revealed.

6. Simplified analyses are very helpful in the stage of preliminary design.

7. Simplified analyses will make PBSD more accessible.

84

On static foundation behaviors

1. Long-term settlements are larger than short-term settlements of deep fdt. where soft soils are encountered.

2. Unless time-dependent effects are interested, staged loads can be used to compute the fdt. displacements.

3. For matrix oriented pile foundation, larger settlements - fdt. center, smaller settlements - fdt. corners. Loading patterns of the piles are just the opposite.

4. Load sharing will be significantly affected by S/D and the length of pile which appear to be the most dominant factors in design.

5. Loads carried by piles also will be affected by geological conditions of the site. Sandy soils and clayey soils will yield different results.

85

On seismic load influences

1. Seismic impacts from the ground soils onto the foundation should be carefully modeled

2. Seismic load influences to all the piles in grouped pile foundation and CPRF are about the same.

3. Smaller pile diameter will result in larger relative foundation displacements w.r.t. the ground.

4. Reducing the length of piles will enlarge the foundation displacement.

5. The number of piles is highly related to S/D ratio. The corresponding effects should be monitored carefully.

86

6. Stiffness and thickness of the softs will not affect much of foundation displacement when end-bearing piles were encountered. Nevertheless, stiffer and thicker soft soils will help to reduce slightly the foundation displacement.

7. Direction of the horizontal seismic load w.r.t. foundation seems to be insignificant. Foundation displacements caused by longitudinal ground excitation is slightly smaller than those occurred along the transverse direction.

8. Existence of the superstructure will generally make smaller foundation displacements. The more rigid the superstructure is (superstructure displacement becomes negligible), the less the foundation displacement will be.

On seismic load influences (contd.)

87

On PBSD

1. PBEE approach is certainly a good tool to PBSD of pile foundation and CPRF.

2. Seismic forces is the most dominant design factor compared to variations of the soil parameters and geological conditions.

3. Moment capacities could be used to guide the design.

4. Productions of artificial EQs become rather important in this case.

5. If Reliability Based approach is interested, MCS can be used. In that case, weights of the IMs must be obtained.

6. Factor of safety of PBSD could be defined. They should be in similar order from PB and RB approaches.

88

References

Byrne, B. and Houlsby, G. (2013) Foundations for Offshore Wind

Turbines, Supergen Wind, 7th Training Event, U. of Oxford.

Frank, R. (2008) Design of Pile Foundations following Eurocode 7 –

Section 7. Workshop “Eurocodes: background and applications”.

Hannigan et al. (2006) Design and Construction of Driven Pile

Foundations- Volume 1, Report FHWA-NHI-05-042.

Orr, T. (2013) Eurocodes: Background and Applications, Worked

Examples – Design of Pile Foundations.

Poulos, H.G. (2001) Method of Analysis of Piled Raft Foundations,

TC18 Report, ISSMGE.

Tomlinson M. and Woodard, J. (2008), Pile Design and Construction

Practice, Taylor & Francis.

陳正興 (2014) “性能設計的理念與架構” 台灣省土木技師公會基樁設計與施工新觀念研討會。

陳正興, 黃俊鴻 (2016) 基礎性能設計, 財團法人地工技術研究發展基金會叢書。

交通部運研所 (2014) 碼頭耐震性能設計手冊, MOT-IOT-103-

H1DB006a。

89

The End

Thanks for your

attentions !

90

from piles to piled raft foundation

Documents