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Tensar International B.V.Design Service Manager –continental Europe
Theo Huybregts
Workshop: TensarSoilDesign theory and methods for reinforced soil retaining walls with block facing
Walls
Steeper than 70 to the horizontal
Normally with concrete facing
Many published design guides
We will look at Bautechnik/2-part wedge
Types of structureDefinitions
Outline of the workshop
2 December 2015Reinforced soil structures design workshop2
Tensar RE500 uniaxial geogrids
Manufactured from HDPE
Strength required for
ULS static
SLS static
Seismic
Tensar uniaxial geogrids
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop3
Long term design tensile strength of polymer geogriddefined as
Pdes (long term design strength)
TB = Tensile (QC) strength
A1 (creep reduction factor, RFCR)
A2 (installation damage, RFID)
(factor of safety = 1.75)
Defining allowable design strength ULS staticBautechnik method
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop4
QC strength measured using test ISO 10319:1996Also used to define design strength for earthquake
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop5
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14
Lo
ad
(kN
/m
)
Strain (%)
Tensile test ISO
10319:1996
Tensar RE560
Defining allowable design strengthLong term creep behaviour
Design parameters for reinforcement
HDPE geogrids are visco-elastic
Long term load strain behaviour is different to short term
This behaviour is determined using creep tests
Simple test: apply load & measure strain
2 December 2015Reinforced soil structures design workshop6
Design parameters for reinforcement
Tests carried out at varying loads
Creep testing laboratories at various temperatures
10C
20C
30C
40C
50C
2 December 2015Reinforced soil structures design workshop7
Defining allowable design strengthLong term creep behaviour
Design parameters for reinforcement
10
100
1E+0 1E+1 1E+2 1E+3 1E+4 1E+5 1E+6 1E+7 1E+8 1E+9
Ru
ptu
re lo
ad
(%
of
ten
sil
e)
Time (hours)
Grade A
Grade B
Grade C
Grade D
Grade E
Grade F
120 years
Mean regression
Rupture load is plotted against time to rupture
Find rupture load for design life = Trup (%)
RFCR = 100/Trup
2 December 2015Reinforced soil structures design workshop8
Defining allowable design strength for ULSLong term creep behaviour - determining A1 = RFCR
Trup
Design life
Tensar RE500 grids @ 20C
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14
Lo
ad
(%
)
Strain (%)
1 month 20 deg C
I month 30 deg C
120 yrs 30 deg C
120 yrs 40 deg C
120 yrs 50 deg C
1 month
120 yrs
1% criterion
2 December 2015Reinforced soil structures design workshop9
Using load-strain data for one month of loading (730 hours) develop isochronous load-strain curve for 1 month
Develop a second isochronous load-strain curve for 120 years
Find load which gives 1% increase in strain from 1 month to 120 years
18.3%
Design parameters for reinforcement
Tensar RE580 @ 20C
Defining allowable design strength for SLSLong term creep behaviour - determining TCS
In accordance with BS 8006-1:2010 and BBA certificate No 99/R109, for retaining walls:
1 month = end of construction
120 years = design life
post-construction strain should be limited to 1%
TCS = 18.3% of QC for Tensar RE580 at 20C for retaining walls
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14
Lo
ad
(%
)
Strain (%)
1 month 20 deg C
I month 30 deg C
120 yrs 30 deg C
120 yrs 40 deg C
120 yrs 50 deg C
1 month
120 yrs
1% criterion
2 December 2015Reinforced soil structures design workshop10
18.3%
Design parameters for reinforcement
Tensar RE580 @ 20C
Defining allowable design strength for SLSLong term creep behaviour - determining TCS
In accordance with BS 8006-1:2010 and BBA certificate No 99/R109, for bridge abutments:
2 months = end of construction
120 years = design life
post-construction strain should be limited to 0.5%
TCS = 11.4% of QC for Tensar RE580 at 20C for bridge abutments
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10 12 14
Lo
ad
(%
)
Strain (%)
2 months 20 deg C
I month 30 deg C
120 yrs 30 deg C
120 yrs 40 deg C
120 yrs 50 deg C
2 months
120 yrs
1% criterion
2 December 2015Reinforced soil structures design workshop11
11.4%
Design parameters for reinforcement
Tensar RE580 @ 20C
Defining allowable design strength for SLSLong term creep behaviour - determining TCS
Determined from full scale site damage trials
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop12
Determined from full scale site damage trials
Fine fill
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop13
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Determined from full scale site damage trials
Medium fill
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop14
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Determined from full scale site damage trials
Coarse fill
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop15
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Determined from full scale site damage trials
5 series of site damage tests were carried out on the RE500 geogrids
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop16
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop17
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14
Lo
ad
(%
)
Strain (%)
Control
Standard compaction
Refusal compaction
Tensar RE560
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Based on comparing tensile strength of control and damaged material
RFID = T/TID
BS 8006-1:2010 Annex D: “Site damage test”
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14
Lo
ad
(%
)
Strain (%)
Control
Standard compaction
Refusal compaction
Tensar RE560
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop18
Control, TDamaged, TID
Defining allowable design strengthInstallation damage factor - determining A2 = RFID
Durability normally investigated to determine resistance to:
Weathering
Microbiological degradation
Oxidation
Liquids (acids and alkalis)
Investigated using
Screening tests (relatively quick)
Long term exposure tests (normally accelerated but may take a long time)
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop19
Defining allowable design strengthDurability - determining RFD
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop20
Defining allowable design strengthDurability - determining RFD
Degradation Test standard
Weathering resistance
BS EN 12224:2000: “Geotextiles and geotextile-related products. Determination of the resistance to weathering”
Resistance to microbiological degradation
BS EN 12225:2000: “Geotextiles and geotextile-related products. Method for determining the microbiological resistance by a soil burial test”
Resistance to oxidation
BS EN ISO 13438:2004: “Geotextiles and geotextile-related products. Screening test method for determining the resistance to oxidation” (56 days at 100C)
Resistance to liquids
BS EN 14030:2001: “Geotextiles and geotextile-related products. Screening test method for determining the resistance to acid and alkaline liquids”
Durability screening tests to ISO Standards
Results in terms of retained strength and failure strain
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop21
Defining allowable design strengthDurability - determining RFD (results for RE500 grids)
Degradation % retained strength % retained failure strain
Weathering resistance
98.5 100.7 99.0 123.2 109.4 120.1
Resistance to microbiological degradation
99.1 102.6 103.1 101.5
Resistance to oxidation
104.1 101.4102.1
102.5 107.1 104.0111.0
110.9
Resistance to liquids- acid
100.4 99.9 104.3 104.8 106.2 109.6
Resistance to liquids- alkali
99.4 99.7 103.1 105.8 107.1 106.8
Design parameters for reinforcement
Exposure of geogrid to UV
During temporary storage on site
2 December 2015Reinforced soil structures design workshop22
Defining allowable design strengthResistance to weathering (exposure)
Design parameters for reinforcement
Exposure of geogrid to UV
Major importance in tropical countries
2 December 2015Reinforced soil structures design workshop23
Defining allowable design strengthResistance to weathering (exposure)
Design parameters for reinforcement
Exposure of geogrid to UV
During installation
2 December 2015Reinforced soil structures design workshop24
Defining allowable design strengthResistance to weathering (exposure)
Design parameters for reinforcement
Exposure of geogrid to UV
During early part of service life
2 December 2015Reinforced soil structures design workshop25
Defining allowable design strengthResistance to weathering (exposure)
Some results from 10 year UV exposure trial at Albury, Australia
Load versus strain curves before exposure
and after 10 years of exposure
Protection provided by minimum 2% carbon black
0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12 14
Lo
ad
(%
)
Strain (%)
Exposed
Control
Design parameters for reinforcement
Tensar 55RE
2 December 2015Reinforced soil structures design workshop26
Defining allowable design strengthResistance to weathering (exposure) - evidence
Importance of using a minimum of 2% carbon black
For carbon black content less than 2% geosynthetics still “look” black
BUT protection rapidly reduces as carbon black content reduces
0
20
40
60
80
100
120
0 1 2 3 4 5 6
% lif
e w
ith
2%
carb
on
bla
ck
Carbon black (%)
HDPE
Design parameters for reinforcement
Range of carbon black content used in TensarRE500 geogrids
2 December 2015Reinforced soil structures design workshop27
Defining allowable design strengthResistance to weathering (exposure) - protection
Based on extensive testing (EP9090 in US), HDPE is inert to all aqueous solutions of acids, alkalis, salts normally found in soil
Very important in tropical climate
Design parameters for reinforcement
2 December 2015Reinforced soil structures design workshop28
Defining allowable design strengthResistance to chemicals - HDPE preferred
Connection
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop49
ConnectionConnection test
NCMA method NCMA SRWU-1
ASTM D6638-01N
T
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop50
VLS system
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop51
VLS system
Mainly frictional
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop52
VLS system
Mainly frictionalConnection
Connection test
NCMA method NCMA SRWU-1
ASTM D6638-01N
T
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop53
VLS system
Mainly frictional
Results from connection tests
Modular block systems connection strength
Design parameters for connection to facing
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80
Co
nn
ecti
on
lo
ad
Tco
n(kN
/m
)
Normal load N (kN/m)
VLS
2 December 2015Reinforced soil structures design workshop54
VLS system
Mainly frictional
Results from connection tests
acs represents mechanical component
cs represents frictional component
Tcmax is maximum
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80
Co
nn
ecti
on
lo
ad
Tco
n(kN
/m
)
Normal load N (kN/m)
VLS
ACS
CS
Tcmax
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop55
Keystone TW3 system
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop56
Keystone TW3 system
Mechanical connection
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop57
TW1 system
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop58
TW1 system
Mechanical connection
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop59
TW1 system
Mechanical connection Connection
N
T
Modular block systems connection strength
Design parameters for connection to facing
Connection test
NCMA method NCMA SRWU-1
ASTM D6638-01
2 December 2015Reinforced soil structures design workshop60
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80
Co
nn
ecti
on
lo
ad
Tco
n(kN
/m
)
Normal load N (kN/m)
VLS
TW1
ACS
CS
Tcmax
TW1 system
Mechanical connection
Results of connection tests
For mechanical connection Acs Tcmax and cs = 0
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop61
TW1 system
Mechanical connection
Results of connection tests
For mechanical connection Acs Tcmax and cs = 0
TUU is geogrid strength using same procedure as connection test
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80
Co
nn
ecti
on
lo
ad
Tco
n(kN
/m
)
Normal load N (kN/m)
VLS
TW1
TuuACS
CS
Tcmax
TUU
Tuu is geogrid strength using same procedure as connection test
Modular block systems connection strength
Design parameters for connection to facing
2 December 2015Reinforced soil structures design workshop62
2 December 2015Reinforced soil structures design workshop68
Tensar International B.V.Design Service Manager –Continental Europe
Theo Huybregts
Workshop: TensarSoilDesign theory and methods for German Institute für Bautechnik method
External stability
Internal stability
Adding earthquake loads
Serviceability
Elements of reinforced soil design
TensarSoil workshopMethod of calculation
3 December 2015Reinforced soil structures design workshop70
Is this method new?
No, it has been in use for more than 16 years
Some of the highest reinforced structures in the world have been designed using the two-part wedge
Design using 2-part wedge methodFinding layout of reinforcement
Method of calculation
3 December 2015Reinforced soil structures design workshop71
Basis of design method
External stability analysis uses the same basic approaches in tie-back wedge and two-part wedge methods
Differences are in the internal stability calculations
Aim: to minimise assumptions required to reach a satisfactory design
Any mechanism used should be admissable and complete (ie. include all forces which are involved)
Original reference: Deutsches Institut für BautechnikCertificate No Z20.1-102
Method of calculation
Design using 2-part wedge methodFinding layout of reinforcement
3 December 2015Reinforced soil structures design workshop72
Surcharge, q
H
Basis for all design methods
Calculations
L
Check external stability to find L
GradeSpacing
Check internal stability to find layout (grade & spacing)
Method of calculation
Design using 2-part wedge methodFinding layout of reinforcement
3 December 2015Reinforced soil structures design workshop73
Surcharge, q
H
Specific design situations
Calculations
L
GradeSpacing
Additional design forces due to earthquakes
High temperature at facing resulting in lower design strength
Method of calculation
Connection strength between facing and reinforcement
Design using 2-part wedge methodFinding layout of reinforcement
3 December 2015Reinforced soil structures design workshop74
Wedge 1
Wedge 2
Surcharge, q
L
hi Coulomb
Inter-wedge boundary
2-part wedge method general procedure
Method of calculation
Hi
i
3 December 2015Reinforced soil structures design workshop75
Wedge 1
Wedge 2
Surcharge, q
L
2-part wedge method general procedure
Method of calculation
Hi
For full analysis this is done by checking wedges at 0.1 intervals
This takes into account complex geometry, c, and isolated surcharge rigorously
i
3 December 2015Reinforced soil structures design workshop76
Surcharge, q
H
G
l
Eah
EavWedge 2
Wedge 1
External stability
Calculations
Method of calculation
External stability check Defined by special case when Hi = H, i = 0
Check sliding on base
Check bearing capacity
L Find L
Check eccentricity of resultant
3 December 2015Reinforced soil structures design workshop77
Surcharge, q
H
L
G
l
Eah
EavWedge 2
Wedge 1
Additional sliding check
Calculations
Check sliding on base
Based on different backs of RSB
Method of calculation
External stability check Defined by special case when Hi = H, i = 0
3 December 2015Reinforced soil structures design workshop78
External stability results
External failure
General overall stability failure
Check with slope stability program
External stabilityFinding size of the reinforced soil block
Method of calculation
3 December 2015Reinforced soil structures design workshop80
Surcharge, q
L
hi
2-part wedge method general procedure
Method of calculation
Hi
Eah
Eav
G
l
R
Z
= for internal stability is set as default, but may be adjusted
i
Internal stability
Look at forces applied to Wedge 2
3 December 2015Reinforced soil structures design workshop82
Surcharge, q
L
hi
2-part wedge method general procedure
Method of calculation
Hi
Eah
Eav
G
l
R
Z
Calculations
Eagh = 0.5Kahi2
Eaph = Kaqhi
Eah = Eagh + Eaph
Eav = Eah tan( - b)
b
i
Internal stability
Look at forces applied to Wedge 2
3 December 2015Reinforced soil structures design workshop83
Surcharge, q
L
hi
2-part wedge method general procedure
Method of calculation
Hi
i
Eah
Eav
G
l
R
Z
Calculations
b
Eah
Eav
G
ql
Z
R
( - i)
Z = Eah
– (G + ql + Eav)tan( - i)
Internal stability
Look at forces applied to Wedge 2
3 December 2015Reinforced soil structures design workshop84
Surcharge, q
L
hi
2-part wedge method general procedure
Method of calculation
Hi
i
Z
Calculations
T3
T4
T5
T6
Add possible resistance from facing
T3 + T4 + T5 + T6
Resistance to Z is provided by four layers of geogrid
So for satisfactory design
Ti = R > Z
Plus any resistance from the facing
Internal stability
Look at forces applied to Wedge 2
3 December 2015Reinforced soil structures design workshop85
Surcharge, q
L
hi
2-part wedge method general procedureDetermining the geogrid resistance
Method of calculation
Hi
i
Z
Calculations
T3
T4
T5
T6
Add possible resistance from facing
T3 + T4 + T5 + T6
Resistance to Z is provided by four layers of geogrid
So for satisfactory design
Ti = R > Z
Plus any resistance from the facing
Internal stability
Look at forces applied to Wedge 2
3 December 2015Reinforced soil structures design workshop87
Surcharge, q Wedge stability
Method of calculation
2-part wedge method general procedureVisualising the mode of wedge failure
3 December 2015Reinforced soil structures design workshop88
Surcharge, q Wedge stability
Method of calculation
2-part wedge method general procedureVisualising the mode of wedge failure
3 December 2015Reinforced soil structures design workshop89
Surcharge, q Wedge stability
Method of calculation
2-part wedge method general procedureVisualising the mode of wedge failure
3 December 2015Reinforced soil structures design workshop90
Surcharge, q Wedge stability
Method of calculation
2-part wedge method general procedureVisualising the mode of wedge failure
Pull-out from facing
Failure through facing
Pull-out from backfill
Rupture of geogrid
3 December 2015Reinforced soil structures design workshop91
Surcharge, q Wedge stability
Method of calculation
2-part wedge method general procedureVisualising the mode of wedge failure
3 December 2015Reinforced soil structures design workshop92
Surcharge, q Wedge stability
Method of calculation
T3
T4
T5
T6
2-part wedge method general procedureAdding resistance from the geogrid
3 December 2015Reinforced soil structures design workshop93
T4
2-part wedge method general procedureAdding resistance from the geogrid - T4
Method of calculation
Look at Geogrid 4 in isolation
3 December 2015Reinforced soil structures design workshop94
T
x
End of geogrid
Slope given byT = 2xvF/FS
Design strength Tal /FS
Connection strength
Tcon /FS
Slope given byT = 2xvF/FS
Envelope of available resistance
2-part wedge method general procedureDeveloping the envelope of available resistance
Method of calculation
T4
F = ptan
x’
3 December 2015Reinforced soil structures design workshop95
T
x
End of geogrid
Slope given byT = 2xvF/FS
Design strength Tal /FS
Connection strength
Tcon /FS
Slope given byT = 2xvF/FS
Method of calculation
T3
2-part wedge method general procedureDeveloping the envelope of available resistance
F = ptan Envelope of available resistance
x’
3 December 2015Reinforced soil structures design workshop96
T
x
End of geogrid
Slope given byT = 2xvF/FS
Design strength Tal /FS
Connection strength
Tcon /FS
Slope given byT = 2xvF/FS
Method of calculation
T6
2-part wedge method general procedureDeveloping the envelope of available resistance
F = ptan Envelope of available resistance
x’
3 December 2015Reinforced soil structures design workshop97
Wedge 1
Wedge 2
Surcharge, q
Hi
i
Internal stability
hi
Which two-part wedge is critical?
How do we choose?
2-part wedge method general procedure
Method of calculation
L
3 December 2015Reinforced soil structures design workshop100
Surcharge, q
Hi
Internal stability
Check for various values of i
Wedges are checked at 3 intervals
2-part wedge method general procedure
Method of calculation
L
3 December 2015Reinforced soil structures design workshop101
Surcharge, q
Hi
Internal stability
Check for various values of Hi
Wedges are checked at every grid level
2-part wedge method general procedure
Method of calculation
L
3 December 2015Reinforced soil structures design workshop102
Surcharge, q
Hi
Internal stability
Sliding between geogrid layers
Sliding between grids is checked at every level
2-part wedge method general procedure
Method of calculation
L
3 December 2015Reinforced soil structures design workshop103
Surcharge, q
Hi
Internal stability
Sliding over geogrid layers
Sliding over grids is checked at every level
2-part wedge method general procedure
Method of calculation
L
3 December 2015Reinforced soil structures design workshop104
Surcharge, q Internal stability
Summary
H
Calculations
Check sliding over geogrid
Check sliding between geogrid
Check families of wedges
Aim is to find layout (grade and spacing) of geogrid
2-part wedge method general procedure
Method of calculation
L
3 December 2015Reinforced soil structures design workshop105
Internal stability results
Assumptions to be considered are:
seismic coefficients to calculate inertia and earth pressure
distribution of inertia and earth pressure
presence of temporary surcharge at the same time as EQ
factors of safety to be used
Pseudo-static design method requires the inclusion of additional static forces to model seismic condition
2-part wedge method general procedureAdding earthquake loads
Method of calculation
3 December 2015Reinforced soil structures design workshop108
Establishing PGALocal seismic codes
Method of calculation
Slovakia seismic hazard
PGA (peak ground acceleration) is the normal starting point for reinforced soil design
Modified as outlined in the following slides
3 December 2015Reinforced soil structures design workshop110
Within the structure Ah & Av
may be amplified or attenuated depending on the mechanism
kh(int)
kv(int)
Ah & AvAccelerations at the base of the structure Ah & Av (up & down)
kh(ext)
kv(ext)
2-part wedge method general procedureAdding earthquake loads
Method of calculation
3 December 2015Reinforced soil structures design workshop111
Sliding on inclined plane between grid
Sliding on grid
Sliding on base
Bearing capacity
Mechanisms which do not cut reinforcement
Use reduced acceleration
2-part wedge method general procedureAdding earthquake loads
Method of calculation
3 December 2015Reinforced soil structures design workshop112
Sliding within reinforced soil block
Two-part wedge
Mechanisms which do cut reinforcement
2-part wedge method general procedureAdding earthquake loads
Method of calculation
3 December 2015Reinforced soil structures design workshop113
For mechanisms which do cut reinforcement displacement would not be acceptable as it would result in rupture or massive distortion of the grid
For these mechanisms some amplification of Ah and Av is allowed for as follows
kh(int) = (1.45 - Ah)Ah for Ah < 0.45
kh(int) = Ah for Ah > 0.45
kv(int) = (1.45 - Av)Av for Av < 0.45
kv(int) = Av for Av > 0.45
2-part wedge method general procedureAdding earthquake loads
Method of calculation
3 December 2015Reinforced soil structures design workshop114
Surcharge, q
L
Method of calculation
Hi
G
l
R
Z
Internal stability
Look at forces applied to Wedge 2
2-part wedge method general procedureAdding earthquake forces
Eah
Eav
3 December 2015Reinforced soil structures design workshop116
Method of calculation
0.5H
H
Distribution of seismic forces
2-part wedge method general procedureAdding earthquake forces
khG*
kvG*
Inertia forces are applied to front 0.5H of reinforced soil block
Only 50% of additional seismic earth pressure forces act
PdynhPdynv
Take 0 or 50% live load
3 December 2015Reinforced soil structures design workshop117
Surcharge, q
L
Method of calculation
Hi
Eah
Eav
G
l
R
Z*
khG*
kvG*
PdynhPdynv
Calculations
Eah
Eav
G
ql
Z*
R*
( - i)
Pdynh
Pdynv
khG*
kvG*
Z* = Eah + khG* + Pdynh – (G + ql+ Eav + Pdynv + kvG*)tan( - i)
2-part wedge method general procedureAdding earthquake forces
Internal stability
Additional forces applied to Wedge 2
3 December 2015Reinforced soil structures design workshop118
Surcharge, q
L
Method of calculation
Hi
G
l
R
Z
Calculations
2-part wedge method general procedureAdding earthquake forces
Internal stability
Comparison with static case
Eah
Eav
G
ql
Z
R
( - i)
Z*
Eah
Eav
3 December 2015Reinforced soil structures design workshop119
Surcharge, q
L
Method of calculation
Hi
Z*
Calculations
2-part wedge method general procedureAdding earthquake forces
Internal stability
Additional forces applied to Wedge 2
T3* + T4* + T5* + T6*
Resistance to Z is provided by four layers of geogrid
Plus any resistance from the facing
So for satisfactory design
Ti* = R* > Z*
*For seismic design geogrid strength is based on short term tensile strength
T3*
T4*
T5*
T6*
3 December 2015Reinforced soil structures design workshop120
View results for different cases
View results for different cases
Surcharge, q For modular block facings
Also gabions
Improving modelling of contribution to stability from the reinforcement depending on facing type
Includes shear resistance
through facing
Resistance from 3 geogrids
Method of calculation
3 December 2015Reinforced soil structures design workshop123
Aim is an economical design but
with adequate margin against
failure and must be serviceable
Factors
Bautechnik design methodOther factors which define the method
Wall friction on back of reinforced soil block (RSB)
= for internal mechanisms
= 2/3 for external mechanisms
Soil strength definition is constant volume for fills (ccv = 0 normally, and cv)
In foundation stability calculation, the inclination factor is included in calculating bearing capacity
Two different load cases (or “load combinations”) are used which affect the distribution of live load (temporary surcharge)
LC A
LC B
3 December 2015Reinforced soil structures design workshop126
Surcharge, q External stability
Similar definitions for internal stability are used
LC A
Factors
Bautechnik design methodLoad combinations which determine the use of LL
Eqh
Eqv
Eh
EvG
Q2
Likely to be critical for
Bearing capacity
Steeper wedges
3 December 2015Reinforced soil structures design workshop129
Surcharge, q External stability
Similar definitions for internal stability are used
LC A maximum overturning
Factors
Bautechnik design methodLoad combinations which determine the use of LL
Eqh
Eqv
Eh
EvG
Q2
Likely to be critical for
Bearing capacity (only used for external stability)
3 December 2015Reinforced soil structures design workshop130
Surcharge, q External stability
Similar definitions for internal stability are used
LC B
Factors
Bautechnik design methodLoad combinations which determine the use of LL
Eqh
Eqv
Eh
EvG
Likely to be critical for
External sliding
Sliding on geogrid
Sliding between geogrid
Less steep wedges
3 December 2015Reinforced soil structures design workshop131
External stability
Similar definitions for internal stability are used
LC C
Factors
Bautechnik design methodLoad combinations which determine the use of LL
Eqh
Eqv
Eh
EvG
Used for serviceability
Post-construction strain check
3 December 2015Reinforced soil structures design workshop133
19m high wall supporting 63m high slope
Designed using two-part wedge method
Thank you!!
Two-part wedge - thinking outside the box
3 December 2015Reinforced soil structures design workshop134
Any questions?