Technologies to Improve Soft

concretecakeUrban and Civil

Nov 29, 2013 (3 years and 7 months ago)

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Recent Advances in Column
Technologies to Improve Soft
Foundations

Jie Han, Ph.D., PE

Professor

The University of Kansas, USA

Outline of Presentation



Introduction




Innovations in Installation and Applications




Load Transfer Mechanisms




Settlement and Consolidation




Stability




Concluding Remarks

Introduction

Definition of Columns

A

vertical

sub
-
structural

element,

installed

in
-
situ

by

ground

improvement

techniques

(replacement,

displacement,

and/or

mixture

with

chemical

agents),

that

carries

the

load

of

the

super
-
structure

or

earth

structure

with

surrounding

soil

and

transmits

it

to

geo
-
media

around

and/or

below,

through

compression,

shear,

or

rotation

Classification of Columns

Method

Type

Technology Examples



Installation

Replacement

Stone columns

Displacement

Sand compaction piles, stone columns

Mixture

DM columns, grouted columns

Combination

Rammed aggregate piers



Material

Granular

Sand compaction piles, stone columns, rammed
aggregate piers

Chemically
-
stabilized

DM columns and grouted columns

Concrete

Concrete columns, cement
-
flyash
-
gravel (CFG)
columns

Composite

Geosynthetic
-
encased soil columns, stiffened DM
columns, and composite spun piles



Rigidity

Flexible

Sand compaction piles, stone columns, rammed
aggregate piers

Semi
-
rigid

DM columns, grouted columns, composite columns

Rigid

Concrete columns

Functions

Densification



Increase

density,

modulus,

strength,

and

liquefaction



resistance

of

surrounding

soil



Increase

pre
-
consolidation

stress

of

surrounding

soil


Pile

effect



Transfer

loads

to

a

deeper

and

competent

geo
-
material




Stress

concentration


Drainage



Accelerate

consolidation




Increase

liquefaction

resistance




Reinforcement




Increase

shear,

tensile,

and/or

bending

resistance

Design Considerations



Load

transfer




Bearing

capacity

(e
.
g
.
,

Bouassida

et

al
.
,

1995
)




Settlement

and

consolidation




Slope

stability




Liquefaction

mitigation

(e
.
g
.
,

Rollins

et

al
.
)




Earth

retaining

(e
.
g
.
,

Shao

et

al
.
)

Innovations in Column Installation

and Applications

T
-
shape Deep Mixed Columns

Rotation
direction
1
2
3
5
6
7
8
Grouting
4
Grouting
Grouting
Grouting
Mixing

Mixing

Mixing

Mixing

Mixing

Mixing

Mixing

Courtesy of S.Y. Liu

T
-
shape Deep Mixing

Courtesy of S.Y. Liu

Hollow Concrete Columns

Courtesy of H.L. Liu

Referred

to

as

Large

Diameter

P
ipe

Pile

Using

C
ast
-
in
-
place

C
oncrete

(PCC)

by

Prof
.

Liu

X
-
shape Concrete Columns

Courtesy of H.L. Liu

Geosynthetic
-
encased Columns

Alexiew et al. (2005)

Composite Columns

Courtesy of G. Zheng

Composite Columns

-

Stiffened Deep Mixed Piles

SDCM pile construction

-
Jet pressure =220 bar

-
Diameter =0.60 m

-

L=7.00 m

Courtesy of Bergado

Composite Columns
-

Grouted Spun Pile

Cement mix

Spun pile

Welding

Bhandari et al. (2009)

Pile
-
Column Combined Method

Huang and Li (2009) and Zheng et al. (2009)

Pile

Column

DM
-
PVD Combined Method

Liu et al (2008)

Embankment
Settlement
plate
E
ar
th pressure cell
P
iezometer
DJM column
Not to scale
PVD
Inclinometer
PVD

DM

column

Ye et al (2008)

The Most Commonly Used Application


Column
-
supported Embankments

Embankment

Columns

Geosynthetics

Geosynthetic
-
reinforced

fill platform

Firm soil or bedrock

D
s
0

D
s

0

Load Transfer Mechanisms

Equal Strain vs. Equal Stress


(a) Equal strain = rigid loading

(b) Equal stress = flexible loading


c


s

S
s

S
s

S
c

E
c

E
c

E
s


c


s

S
s

S
s

S
c

E
c

E
c

E
s

Columns

D
S

How about a column
-
supported embankment?

Stress Concentration Ratio, n =


c


s

n =

D
c

D
s


c


s

D
c

D
s

S
c

= S
s

n



E
c

E
s

Stress Concentration under Equal V. Strain

E
c

E
s

S
c

= S
s


h


c


s


z

=


c

D
c

=


s

D
s


z

=


z

-


(

x

-


y
)

E
c


z

-


(

x

-


y
’)

E
s

=

1
-
D unit cell

Unit cell with lateral deformation

>

Stress Concentration Ratio vs. Strain


Stress

Strain


c1


s1


s2


c2


s3


c3


c4


s4

s
c
n



Yielding

Stress concentration ratio, n

Strain

0

(a) Stress
-
strain relationship

(b) Stress concentration ratio

Yielding

Column

Soil

Equal vertical strain condition

E.g., stone column: q
cult

= 15 to 25 c
u
, q
sult

= 5 to 6 c
u

n = q
cult

/ q
sult

= 2 to 5

Influence of Column Lateral
Deformation and Yielding

Castro and Sagaseta (2011)

Stress concentration ratio, n

Influence of Modulus Ratio

and Column Yielding

Jiang et al. (2010)

0
10
20
30
40
50
60
70
0
.
1
1
10
100
1000
10000
100000
Stress concentration ratios
Time (days)
10
50
100
E
c
/E
L/d
e
=
4
a
s
=
0
.
1
k
c
/k
v
=
1
Rigid

column

Semi
-
rigid

Flexible

Stress Concentration vs. Consolidation

Yin and Fang (2008)

20 kPa

40 kPa

n vs. E
c
/E
s


0
1
2
3
4
5
6
7
8
9
10
0
10
20
30
40
Stress Concentration Ratio,
n
Modulus Ratio,
E
c
/
E
s
Barksdale and Bachus (1983)
n
= 1 + 0.217 (
E
c
/
E
s
-
1
)
Cutoff ratio

for stone columns

Stress Transfer

under Unequal Vertical Strain

Settlement, S(z
)
S
s
S
c
Shear stress,
t
(z
)
Equal settlement
(upper plane)
Equal settlement
(lower plane)
t
< 0

0

c

f

s
Fill
Average vertical
stress,

(
z)
r
c
r
e
t
> 0
z
z
z
S
c
at r
<
r
c
S
s
at r = r
e
t
at r =
r
c

c
at r
<
r
c

s
at r = r
e
h
c
Soft
soil
Bearing layer
Column
Modified from Schlosser and Simon (2008)

Modified from Han (1998)

W

t

t

p
s

H


s


c

T

H
cr



Stress Transfer in Geosynthetic
-
reinforced

Column
-
supported Embankment

Effects
:

(
1
)

modulus

ratio

effect,

(
2
)

soil

arching,




(
3
)

tensioned

membrane/slab

stiffening

E
c

E
s

Field Stress Concentration Ratio


0
10
20
30
40
50
60
70
0
100
200
300
400
500
600
Stress Concentration Ratio, n
Applied pressure,
p (
kPa
)
All plate loading test data from Han and Ye (1991)
Flexible
column
PLT/lime columns
PLT/stone columns
Semi
-
rigid
column
PLT/
DM
columns
GCSE/
DM
columns
Rigid
column
PLT/VCC
PLT/concrete
columns
GCSE/VCC
GCSE/concrete
column
s
CSE/concrete
column
s
PLT = Plate
loading test
CSE
= Column
-
supported
embankment
GCSE
=
Geosynthetic
-
reinforced
column
-
supported
embankment
Findings
:


(
1
)

n

increases

with

stress

level



(
2
)

n

increases

with

rigidity

of

loading

Han and Wayne (2000)

DEM Modeling of Dynamic Behavior

PFC2D 3.10
Step 69970 22:11:09 Tue Sep 29 2009
View Size:
X: -6.307e-001 <=> 2.360e+000
Y: -8.952e-001 <=> 2.554e+000
Wall
Wall
Ball
Measurement Circles
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
1.3m
0.3 m
0.9 m
0.3 m
0.3 m
Embankment
Pile cap
Optional
geogrid
0
1
2
3
4
5
6
7
8
9
0
5
10
15
20
25
30
Stress concentration ratio

Cycle

Unreinforced
Reinforced
Loading

Findings
:


(
1
)

geosynthetic

increases

rigidity

of

loading



(
2
)

n

decreases

with

soil

arching

Settlement and Consolidation

Methods of Settlement Calculation


1
.

Stress

reduction

factor

(e
.
g
.
,

Aboshi

et

al,

1978
)


2
.

Improvement

factor

method

(e
.
g
.
,

Priebe,

1995
)


3
.

Elastic
-
plastic

solution

(e
.
g
.
,

Pulko

and

Majes,

2005
;



Castro

and

Sagaseta,

2009
)



4
.

Column

penetration

method

(e
.
g
.
,

Chai

et

al
.
,

2010
)


5
.

Pier
-
raft

method

(e
.
g
.
,

Han

et

al
.
,

2009
)


5
.

Numerical

method

Stress Reduction Factor Method


Settlement of untreated ground

Settlement of treated ground

If assume m
v,s

= m
v,s


Stress reduction factor

Aboshi et al. (1978)

Settlement ratio

H
m
s
z
s
,
v
s

D

H
m
H
m
s
z
s
'
s
,
v
'
z
'
s
,
v
sc

D



D

s
s
,
v
'
s
,
v
s
sc
m
m
s
s


)
1
n
(
a
1
1
s
s
s
s
s
sc





Stress Reduction Factor Method

vs. Numerical Method

Jiang et al. (2013)

0
50
100
150
200
250
300
0
20
40
60
80
100
Consolidation settlement (mm)
E
c
/E
Numerical
Simplified
H/d
e
= 4
a
s
= 0.1
k
c
/k
v
= 1
E
c
/
E
s

Improvement Factor Method

Priebe (1995)

Assume

incompressible

columns

with

bulging

over


column

length

Basic Method


















1
2
/
45
tan
a
1
4
a
5
a
1
I
c
o
2
s
s
s
f
Improvement


factor

f
s
sc
I
s
s

Settlement

of

stone

column


foundation

Modified Method

In

addition

to

column

bulging,

column

compressibility


and

overburden

stress

are

considered

Basic Improvement Factor Method

Priebe (1995)

1
2
3
4
5
6
7
8
0
0.1
0.2
0.3
0.4
0.5
Improvement Factor

Area Replacement Ratio

35
37.5
40
42.5
45
Friction angle

of column (deg.)

Elastic
-
Plastic Solution for

Stone Columns

Pulko and Majes (2005)

Castro and Sagaseta (2009)



Assume

soft

soil

is

linearly

elastic




Assume

stone

columns

are

linearly

elastic
-
perfectly



plastic

with

Mohr
-
Coulomb

failure

criterion

with

a



constant

dilantancy

angle




Plasticity

starts

with

the

upper

portion

of

the

column

and


can

extend

deeper

to

the

whole

length

of

column

with


applied

load

Column Penetration Method

Chai et al. (2010) and Chai (2012)

H
c

= H
L

f(

) g(

) h(

)

Equivalent

unimproved


zone

thickness

due

to

column

penetration

Area

replacement

ratio

Improvement

depth ratio

Pressure

strength ratio

Pier
-
raft Approach for Settlement of Soil
-
cement or Concrete Columns

Han et al. (2009)



g
tp
s
p
s
eq
A
A
E
E
E
E







2
cp
p
r
cp
r
p
pr
r
p
pr
K
/
K
1
2
1
K
K
S
P
P
K








Horikoshi and Randolph (1999)

Randolph (1984)

Raft

E
s

d
eq

E
eq

A
g

Calculated Settlements by Pier
-
raft Aproach

Method

Group

Equivalent pier

Analytical

Numerical

Settlement (cm)

15.9 (16.9*)

15.6

16.9

* Without considering finite depth effect

Han et al. (2009)

10m

10m

0.8m

7.4m

(a) Plan view

0.5m

L
p

=10m

DM columns

(E
p
=100MPa)

Raft

(b) Cross section

h = 30m

15MN

E
s
=5MPa

Consolidation of Stone Columns

(Han and Ye, 2001; 2002)

d
e

2H

z

H

r
c

r

r
e

k
v

k
h

Drainage surface

Drainage surface

Stone column

p

r
s

k
s

k
c

E
c

E
s

Rate

of

consolidation


due

to

radial

flow
:


'
r
'
m
T
)
N
(
F
8
r
e
1
U



2
e
'
r
'
r
d
t
c
T

Modified

time

factor


in

radial

flow










1
N
1
n
1
c
c
2
s
r
'
r
Degree of Consolidation

0
0.2
0.4
0.6
0.8
1
0.0001
0.001
0.01
0.1
T
r
U
Balaam and Booker (1981)
Han and Ye (2001)
Barron (1947)
n=10
n=1
Han & Ye (2001)

Khine (2004)

Free
-
draining

stone column

Dissipation of Excess Pore Pressure

0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
0.02
0.04
0.06
0.08
0.1
0.12
Time Factor, T
r
Dissipation of Average Excess Pore
Water Pressure,
D
u/p
Due to drainage
Due to stress reduction
N=3, n
s
=5
Han and Ye (2001)

Well Resistance Effect

0
10
20
30
40
50
60
70
80
90
0
20
40
60
80
100
120
Settlement (mm)

Time (day)

Field data (Tan et al., 2008)
No well resistance (Han and Ye, 2002)
Well resistance (Han and Ye, 2002)
Han (2010)

Consolidation of Column
-
improved
Soft Foundation over Soft Soil

Chai and Pongsivasathit (2009)

Zhu

and

Yin’s

(
1999
)

closed
-
form

solution

for

consolidation


of

two
-
layered

soils

can

be

used

for

calculation

of


consolidation

rate

Consolidation of Soil
-
cement

Column
-
improved Foundations

Jiang et al. (2013)

0
10
20
30
40
50
60
70
80
90
100
0.0001
0.001
0.01
0.1
1
Time factor T
v
=c
v
t/H
2
Average degree of consolidation (%) .
5
10
50
100
E
c
/E
s
k
c

= k
s

Stability

Column Failure Modes

under Embankment Loading

Modified from Kitazume (2008) and Broms (1999)

Embankment
Soft soil
Stiff layer
Columns
Sliding direction
Embankment
Soft soil
Columns
Stiff layer
Embankment
Soft soil
Columns
Stiff layer
Embankment
Soft soil
Stiff layer
Columns
Embankment
Soft soil
Stiff layer
Columns
(a) Sliding
(b) Collapse (rotational)
(c) bending
(d) Circular shear
(e) Horizontal shear
Columns
Embankment
Berm
Tensile
failure
Bending
failure
S
o
(f) Combined
Factor of Safety under Undrained
Condition for Stone Columns

Abusharar and Han (2010)

Backfill
Equivalent area
Sand
water level
Clay
b
Sand
Backfill
Stone columns
water level
Clay
a
FS (individual) = 0.9 FS (equivalent)

Numerical Modeling with DM Columns

Han et al. (2005; 2010)

0
1
2
3
4
5
6
0
100
200
300
400
500
600
Cohesion of DM Walls (kPa)
Factor of Safety
Numerical
Bishop
Shear
Bending
Rotation
Centrifuge Tests with Rigid Columns

Zheng et al. (2011)

Single column

Column group



Concluding Remarks



A

variety

of

column

technologies

have

been

developed


and

successfully

adopted

for

different

applications



Composite

columns

or

combined

technologies

with



columns

have

been

increasingly

used

to

combine

their


advantages



Stress

concentration

ratio

depends

on

rigidity

of



loading,

modulus

ratio,

lateral

deformation,

yielding

of



columns,

stress

level,

and

dynamic

loading



Columns

can

accelerate

the

rate

of

consolidation



through

drainage

and/or

stress

transfer


Columns

under

embankment

loading

can

fail

under


shear,

tension,

bending,

rotation,

or

a

combination
.



Bending

and

rotation

failure

are

dominant

for

semi
-


rigid

and

rigid

columns

Thank You!