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Column-Supported Embankments: Past, Present, and Future

Jie Han, Ph.D., PE, ASCE Fellow

Professor

The University of Kansas

Column-Supported Embankments

Also referred to as

Pile-Supported Embankments

Piled Embankments

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Differential Settlement

Approach Slab

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Bump over Piled Culvert

Courtesy of Gue, S.S.

Conventional Pile-Supported Embankments

Firm soil or bedrock

Embankment

Vertical piles

s0

s

Large sizePile caps

Inclinedpiles

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Geosynthetic-Reinforced Column-Supported (GRCS) Embankments

Firm soil or bedrock

Embankment

columns

Geosynthetics

Geosynthetic-reinforcedfill platform (alsoLoad Transfer Platform)

s0

s0

Small sizePile caps

Masada in Israel

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Masada in Israel

“According to Josephus, the Siege of Masada by troops of the Roman Empire towards the end of the First Jewish–Roman War ended in the mass suicide of 960 people.” (Wikipedia)

Masada Bathhouse in Israel

Built between 37 and 31 BCE (before the Common Era)

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Construction of Road over Peat in Holland

Courtesy of Suzanne van Eekelen

23 December 1935: How to construct a road in the Krimpenerwaard?

Based on 6 CPTs, Keverling Buisman thinks: using a fascine mattress

Keverling Buisman(1890 – 1944)

fascine mattress:80 cm thick reed

Fascine Mattress

Courtesy of Suzanne van Eekelen

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Courtesy of Suzanne van Eekelen

1937: second thought after taking more CPTs: road on piles. Keverling Buisman wrote:

to ‘prevent complaints and unfavourable comments’

‘piled road would meet more ‘appreciation’’

Second Thought

Keverling Buisman(1890 – 1944)

Courtesy of Suzanne van Eekelen

Pile-supported Embankment

Timber piles (upside down to get sufficient bearing

capacity)

Concrete

Sand

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Design Guideline for Piled Embankments

Rathmayer, H. (1975), “Piled embankment supported by single pile caps,” Istanbul Conference on Soil Mechanics and Foundation, Istanbul, Turkey, 1975.

Height of Coverage by pile caps (%)Embankment

(m) Crushed stone fill Gravel fill

1.5 to 2.0 50 to 70 >702.0 to 2.5 40 to 50 55 to 702.5 to 3.0 30 to 40 45 to 553.0 to 3.5 30 to 40 40 to 453.5 to 4.0 >30 >40

Bridge Approach Support Piling

Reid and Buchanan (1984)

Bridge

Concrete Pile StructuralEmbankmentSupport Piles

TransitionalEmbankmentSupport Piles

GeosyntheticFill

Soft Alluvium

First documented column-supported embankment with geosynthetic reinforcement

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Westway Terminal

The first application of column-supported embankments (CSE) with geosynthetic reinforcement in the United States was in 1994 for the Westway Terminal in Philadelphia, PA.

Courtesy of James Collin

Westway Terminal

Courtesy of James Collin

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Westway Terminal

Courtesy of James Collin

Westway Terminal

Courtesy of James Collin

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Hewlett, W.J. and Randolph, M.F. (1988). “Analysis of piled embankments.” Ground Engineering. 21(3): 12-18.

British Standards Institution BS8006 (1995). Code of Practice for Strengthened/Reinforced Soils and Other Fills. London, U.K.

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SCI Web of Science citations: 70, Google citations: 257 (by June 17, 2013)SCI Web of Science citations: 91, Google citations: 322 (by March 20, 2014)SCI Web of Science citations: 131, Google citations: 411 (by December 7, 2015)SCI Web of Science citations 146, Google citations: 428 (by April 20, 2016)

s, H, J, Ep, Es investigated

Applications

Reid and Buchanan (1984)

Bridge

Concrete Pile StructuralEmbankmentSupport Piles

TransitionalEmbankmentSupport Piles

GeosyntheticFill

Soft Alluvium

ExistingNew

VCC Column

Geosynthetic

Han & Akins (2002)

Tsukada et al. (1993)

Soft alluvium

Geosynthetic

Pavement

Subgrade

Soil-cement column

Centerline Storage tank

Medium dense sand and gravel layer

Vibro concretecolumn

Soft organicsilt & peat

GeosyntheticsRingwallfooting

ASCE G-I (1997)

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Courtesy of Chris Dumas

Piles and Caps

Geosynthetics

Design of Geosynthetic-reinforced Column-Supported Embankments

Fill

Columns

Fill

Load Transfer Platform Design

Columns

Column Foundation Design

Single-layer reinforcement Multi-layer reinforcement

Geosynthetic

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Soil Arching, Stress Concentration and Tensioned Membrane Effect

Modified from Han (1998)

W

pb

H

sc

THcr

= pb/(H)Soil arching ratio

Critical height Hcr

Contributions of Geosynthetics

Tensile resistance:- Reduce lateral thrust on columns

Tensioned membrane effect:- Reduce differential settlement- Transfer load onto columns- Stabilize soil arch

Column

Reversely tensioned membrane effect:- Prevent soil yielding above columns

Tensile anchorage:- Stabilize slope

Column

Stiffened platform or plate effect:- Include all the above contributions

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Development of Soil Arching

Low Embankment

No deformation Small deformation Large deformation

Hcr

Hcr

High Embankment

No deformation Small deformation Large deformation

Hcr

Hcr

Hcr and vs. Displacement

Displacement

1.0Hcr/H

Low embankment

High embankment

Fully-mobilized soil arch

Partially-mobilizedsoil arch

Hcr/H

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Courtesy of Huesker

Courtesy of Huesker

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Critical Height

Hcr

s-a

Equal settlement plane

Equal stress

s

Vertical stress

SettlementDepth

Depth

HcrCapSoil

Hcr

Cap Soil

Equal stress

Equal settlement

Critical Height

Chen et al. (2016)

Hcr

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Lab settlement data (Chen et al., 2007):

Hcr > (1.4 to 1.6) (s – a)

Critical Height

Field earth pressure data (Chen et al., 2010): Hcr > (1.1 to 1.5) (s – a)

BS8006: Hcr > 1.4 (s – a)s-a

Equal settlement plane

Hcr

Hewlett and Randolph (1988): Hcr > 1.0 (s – a)

Equal stress

s

Lab settlement earth pressure data (Xu et al., 2016): Hcr > (1.1 to 1.5) (s – a)

Failure case: H 0.7(s-a) (Camp and Siegel, 2006)

Possible Problems

Courtesy of Gue, S.S.

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Lab Study

Filz et al. (2012)

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Field Study

Sloan (2011)

Sloan (2011)

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Sloan (2011)

Critical Height

s’/d

H/d

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Modeling of Soil Arching

BS8006 (1995)Adopted Terzaghi

H

pb pb

Hewlett and Randolph (1988)

pcpc

Soil arching ratio, = pb/(H+q)

q q

KTz

as

Modeling of Soil Arching

2-D 3-D

Miki (1997)

=60o

Carlsson (1987)

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Multiple Soil Arching Model

Zaeske and Kempfert (2002)

Chen et al. (2008)

hhe

L

z

Innercolumn

Outercolumn

Ground surface

Equal settlement plane

Top of embankment

Cap

Pile Soft soil

DpDi

Do

So+Ws(0)=Si+Wp(0)

Ground surfaceafter settlement

Equal settlement plane

Top of embankment

Pile Soft soil

FF dz

Pi

Pi+ΔPi

Ws(0)Wp(0)Se

Wp(L)

Ws(L)

Unit Cell Model

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Comparison of Soil Arching Ratio

Modified from Filz & Smith (2005)

0.25 0.33 0.50a/s

H/s 1.5 4 1.5 4 1.5 4

BS8006

Adopted Terzaghi(KT = 1)

Adopted Terzaghi(KT = 0.5)

Kempfert et al.

Hewlett & Randolph

Carlsson

0.92 0.34 0.62 0.23 0.09 0.02

0.60 0.32 0.50 0.23 0.34 0.13

0.77 0.52 0.69 0.42 0.54 0.26

0.55 0.46 0.43 0.34 0.23 0.15

0.52 0.48 0.43 0.31 0.30 0.13

0.47 0.18 0.42 0.16 0.31 0.12

Sloan (2011)

Measured vs. Calculated Vertical Stresses

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Comparison of Load Share Ratio

Chen et al. (2008)Load share ratio = pile load/total load

Concentric Soil Arching Model

Van Eekelen (2015)

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Concentric Soil Arching Model

for Vertical Stress Distribution

van Eekelen (2015)

Vertical Stress Distribution

Han and Gabr (2002)

Pile

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Stress Distribution Model

Findings: Inverse triangular stress distribution abovegeosynthetic reinforcement resulted in the shapeof deformed geosynthetic matching the measured

van Eekelen et al. (2012)

Triangular

Uniform

Inverse triangular

Tensioned Membrane Theory

T T

pb

6

11

2

LpAT bc

L = s -a

BS8006 (1995, 2010)

Ac = relative coverage area of reinforcement(Ac = 1 for 2D)

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3D Relative Coverage Area

as

L = s-a

a2

as1Ac

Rogbeck et al. (1998)

T

Tension in Single Reinforcement

Columns

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Tension in Single Geosynthetic

Liu et al. (2007)

0

500

1000

1500

2000

0 100 200 300 400 500 600 700 800 900Strain ()

Distance (mm)

2; N

6; N

10; N

14; N

5; E

10; E

15; E

Displacement of trap door  (mm); N = Numerical, E = Experimental

Bhandari (2010)

Han and Gabr (2002)

Chen at al.(2016)

X-tension in the lower layer

Tension in Multiple Reinforcements

X-tension in the upper layer

Huang et al. (2005)

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Tension in Multi-layer System

Pile cap

Geosynthetic layers

d

a

c

b

Pile cap

Geosynthetic layers

d

a

c

b

0

5

10

15

20

25

30

35

40

0 2 4 6 8

Distance from the toe (m)

Ten

sio

n in

geo

gri

d (kN

/m)

lower layer

upper layer

Huang et al. (2005)

Borgesn & Gonçalves(2016) confirmed this phenomenon.

Effect of Foundation Soil Resistance

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7

Center to center spacing of columns, s(m)

Ten

sio

n in

rei

nfo

rcem

ent

(kN

/m) Height of

embankment (m)

10.5

6.5

10.5

6.52.5

2.5

No contribution from foundation soil

Partial support from foundation soil (soft clay)

Jones et al. (1990)

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Calculated vs. MeasuredStrains in Geosynthetic Reinforcement

More foundation soil resistance Less foundation

soil resistance

van Eekelen et al. (2015)

Concentric soil arching model

+

Design MethodMainly based on the research done by Smith (2005) and Filz and Smith (2006, 2007)

Adapted Terzaghi Method to estimate vertical stress on top of geosynthetic

1D compression of pile and soil

Force equilibrium and deformation compatibilityabove and below geosynthetic

Spreadsheet GeoBridgerequired for calculations

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DEM Modeling of Dynamic Behavior

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 m0.3 m 0.3 m

Embankment

Pile cap

Optional geogrid

Numerical model of a GRCS embankment Total number of particles = 11,793 Bhandari and Han (2010)

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25 30

Stress concentration ratio

Cycle 

Unreinforced

Reinforced

0

2

4

6

8

10

12

14

16

18

20

0 0.3 0.6 0.9 1.2 1.5

Tension  (kN

/m)

Distance (m)

0

5

10

15

20

25

No. of cycle

Cyclic Loading

Bhandari and Han (2010)

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Cyclic Loading

Chen et al. (2016)

increase

Future Research

Settlement calculation

Under dynamic loading (traffic & earthquake)

Multiple geosynthetic reinforcement layers

Different column type and stiffness effects

Floating columns

Column pattern

Down drag force effect

Stability analysis

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Future Research

Concluding Remarks There is a long history for the concept of column-

supported embankments.

Column-supported embankments have been

increasingly used and researched.

Significant progresses have been made in soil arching

theory, vertical stress distribution, and tensile strain

distribution in geosynthetic reinforcement.

Reliability of design methods has been improved.

Critical height is an important parameter for design and

field performance.

Further research is still needed.

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Thank You!