2021 southwest geotechnical engineering conference design

6/24/2021

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Design of geosynthetic-reinforced column-supported embankments:

A unified approach

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

Glenn L. Parker Professor

The University of Kansas

2021 Southwest Geotechnical Engineering Conference

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2005

Theory

Practice

The 3rd Robert M. Koerner Award LectureGeosynthetic‐Reinforced Column‐Supported Embankments: Bridging Theory and Practice

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Introduction Mechanisms and Mechanics Theoretical Solutions Unified Design Procedure Concluding Remarks

Outline of Presentation

Introduction

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Common Field Problems

Different settlement is a common problem for geotechnical applications.5

Bridge

Piles

Fill

Columns

Bridge

Piles

Fill

Piles

Load transfer platform (LTP)

Pile/Column-Supported Embankments

Pile-supported embankmentor piled embankment

Column-supported embankment

Basal reinforced Geosynthetic-reinforced

Geosynthetic Geosynthetic

The term “geosynthetic-reinforced column-supported embankments (GRCSE)” is used in this presentation. 6

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Column-Supported EmbankmentsCourtesy of Mr. C. Dumas

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Type of Column

Credit: D. Alexiew

Credit: J. Collin

This presentation is mostly based on rigid columns. 8

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Common Applications

Reid et al. (1993)

Bridge

Concrete PilePiles

GeosyntheticFill

Soft soil

ExistingNew

ColumnGeosynthetic

Han & Akins (2002)

Tsukada et al. (1993)

Soft soil

GeosyntheticPavement

Subgrade

Column

CenterlineStorage tank

Firm soil

VCCSoft organicsilt & peat

GeosyntheticsRingwallfooting

ASCE G-I (1997)

grouted column

Geosyntheticreinforcedplatform

Uniaxial geogrids

Traffic loading

Soft soil

Alzamora et al. (2000)

Uncontrolled fill

Firm soil

Compacted fillPipes

Zhou (2019) 9

Column Coverage

Ac

Column coverage= Ac/A x 100%

0

10

20

30

40

50

60

70

80

0 5 10 15

Cov

erag

e by

pile

(ca

ps)

(%)

Height of embankment (m)

Crushed stone fillGravel fillRecent projects

Constructed geosynthetic reinforced column-supported embankments

Guidelines for conventional pile supported embankments

(Rathmayer, 1975)

Modified from Han and Gabr (2002)10

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Contributions of Geosynthetics

Tensile resistance:- Reduce lateral thrust on columns

Tensioned membrane:- Reduce differential settlement- Transfer load onto columns- Minimize downdrag force- Stabilize soil arch

Columns

Reversely tensioned membrane:- Prevent soil yielding above columns

Tensile anchorage:- Stabilize slope

Columns

Stiffened platform:- Include all the above contributions

Lateral restraint:- Minimize lateral soil movement

Columns

Column

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Mechanisms and Mechanics

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Load Transfer Mechanisms

= ps/(H+q0)Soil arching ratio

Critical height HcrStress concentration ratio n = c/s

SRR = s/(H+q0)Stress reduction ratio

Modified from Han (1999)

W ps

H

sc

THcr

Column

Fill

GeosyntheticReinforcement(GR)

q0

dd

Soil arching

Tensioned membrane

Column-soil interaction

Column modulus effect

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Mechanisms

Progressive Development of Soil Arching

Han, Wang, Al-Naddaf, Xu (2017)

H

B

q

v

1

2

3

Normalized displacement,

Soi

l arc

hing

rat

io,

Initialarching

Maximumarching Stress recovery

Ultimatestate

min

min

ult

ult

Simplified

1.0

10%B

Terzaghi’ssolution

Iglesia et al. (1999)

(1.5%-5%)B

Plane-straincondition

1

2

3

4

0

This curve is called “Ground Reaction Curve (GRC)”.

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Ye, Wang, Zhang, Han, Xu (2020)

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

(King et al., 2017 modified from McGuire, 2011)

Critical Height

s’ = half diagonal clear distance

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McGuire (2011): Hcr = 0.81s + 0.98a

Square pattern

Tensioned Membrane Effect

Courtesy of Huesker & Dr. Dimiter Alexiew16

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Column Shape & Pattern Effect2.05% 1.13%

1.78% 0.97%Zhang, Wang, Ye, Han (2019) 17

Strainstrips

Circular columns with triangular pattern induce lowest tensile strain and strain strips should be used for calculation of GR strains.

Monitored Axial Loads in ColumnsChow, Han, Reuter (2020)

s

P

z

Neutralplane

= 0

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Theoretical Solutions

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Existing Soil Arching Models

Terzaghi (1943) Carlsson (1987)Hewlett & Randolph (1988)

Yielding

Adapted TerzaghiRussell et al. (2003)*Sloan (2011)* Filz et al. (2019)*FHWA method*

Guido CollinJenner-BushSwedish MethodFHWA beam methodJapanese method

BSI method (2010)Abusharar et al. (2009)Zhuang & Cui (2014)

Chen, Chen, Han, Xu (2008)*

*consider column-soil interaction and load-displacement compatibility 20

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Existing Soil Arching Models

Van Eekelen et al. (2013)Zaeske (2001) and

Kempfert et al. (2004)

Germany method - EBGEO Dutch method - CUR 226 (2016)- Concentric arch model

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Calculated Stresses by Methods

Modified from McGuire & Filz (2008)

Van Eekelen et al.

(K = 1.0)

(K = 0.5)

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H

s = 2.5 m

a = 1.0 m

= 19 kN/m3, = 35o

Square pattern

GR ps

The main reason for the calculation differences is that the soil arching models were developed at different arching stages.

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Proposed GRC for Arching

Displacement, /(s-a)

0.025 0.1

Determined by the adapted Terzaghi method

Determined by the concentric soil arch method

Normalized stress, /(H+q0)

1.0

Modified from Han, Wang, Al-Naddaf, Xu (2017)23

Design Procedure

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Design Procedure: Step 1

H

q0

, J

L

a

s

, , e0,Cc, Cr

McGuire (2011): Hcr = 0.81s + 0.98a (square pattern)25


Average displacement,

Stress,

H+q0

0.1(s-a)

Subsoil settlement

Subsoil support

'0'

0 0

log1

c z avs

z

C z

e

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Stress on subsoil av

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Average displacement, 0.025(s-a) 0.1(s-a)

Determined by the adapted Terzaghi method

Determined by the concentric soil arch method

Soil arching

Stress,

H+q0

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Average displacement, 0.1(s-a)

Geosynthetic support

3

4

64

3

g gs

J

s a

Stress,

H+q0

Average net applied stress above geosynthetic

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Net stress above geosynthetic, Δs

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Average displacement, 0.1

Combined support

Combined

SubsoilGeosynthetic

Stress,

H+q0

Subsoil + Geosynthetic

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Average displacement,

Stress,

0.1

Combined

Calculated

Calculated s

2

2

ss

gs

s a

a s a

22

3

24gs g

g

J s aT

Stress on strips

Tension & strain in strips

H+q0

gg

g

T

J

Determine stress & displacement

ps

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Case Study 1 – Full-Scale Experiment

Briançon, Simon (2012) and Rowe, Liu (2015)

H = 5 m (16.4 ft), H1 = 0. 55 m (1.8 ft), a = 0.34 m (1.1 ft), s = 2.0 m (6.6 ft), = 19 kN/m3 (121 pcf), = 30o – 36o, Jg = 800 kN/m (55 kips/ft)

CMCSCCG

h (m)

1.5

1.06 ‐ 8

(kN/m3)

19.614.1

20.8

w (%)

3160

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PI (%)

22

12

(o)30.6

27

c (kPa)

4

1330.6 4

34 020.0

Layer

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Case Study 1 – Full-Scale Experiment

0102030405060708090

100

0 0.05 0.1 0.15 0.2

Ve

rtic

al s

tres

s (k

Pa)

Differential settlement at embankment base (m)

Soil archingReinforcementSubsoilSubsoil + reinforcement

Measured Calculated

Stress on geosynthetic

55 kPa(8.0 psi)

59 kPa(8.6 psi)

Differential settlementbetween column/soil

41 mm(1.6 in)

43 mm(1.7 in)

Strain ingeotextile (%)

0.2-0.7 0.2-0.4

ps,min = 59 kPa (8.6 psi) (Concentric Arch Model)

ps,ult = 68 kPa (9.9 psi) (Adapted Terzaghi model)

ps,minps,ult

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Case Study 2 – Woerden Project

Van Eekelen et al. (2020) 33

0.75-m (2.5-ft) thick fill for the working platformcaused excessive subsoil settlement (void)

H = 1.78 m (5.8 ft) a = 0.75 m (2.5 ft)s = 2.24 m (7.3 ft) = 18.3 kN/m3 (116 pcf) = 51o

Jg = 4,717 kN/m (323 kips/ft)

Case Study 2 – Woerden Project

0

10

20

30

40

50

0 0.05 0.1 0.15 0.2

Ve

rtic

al s

tres

s (k

Pa)

Differential settlement at embankment base (m)

Soil arching

Reinforcement

Subsoil

Subsoil + reinf.

Measured Calculated

Stress on geosynthetic

9.4 kPa(1.4 psi)

11.1 kPa(1.6psi)

Differential settlementbetween column/soil

85 mm(3.3 in)

83 mm(3.3 in)

Strain ingeotextile (%)

0.5-0.8 0.8-1.3

ps,min = 8.6 kPa (1.2 psi) (Concentric Arch Model)

ps,ult = 15.0 kPa (2.2 psi) (Adapted Terzaghi model)

ps,min

ps,ult

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Concluding Remarks Geosynthetic-reinforced column-supported embankments

(GRCSE) are a complex system and have been a hot research topic and increasingly used in the practice in the past 20 years.

Recent research has helped better understand load transfer mechanisms in GRCSE, especially soil arching.

Ground reaction curve is important for describingprogressive development of soil arching with displacement.

A unified design procedure considering progressive development of soil arching, tensioned membrane, subsoil support, and column-soil interaction (downdrag) is proposed, which bridges theory and practice. 35

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Questions?

[email protected]

Thank you!

2021 southwest geotechnical engineering conference design

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