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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!
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