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8/13/2019 S 3-3 Pavement Design in UK & Future Developments A_Collop
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Pavement design in the UKand future developments
Andy CollopProfessor of Civil EngineeringDirector of NTEC
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Outline
Standard UK pavement design
Foundation Upper pavement
Long Term Pavement Performance Model(LTPPM)
Summary
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UK pavement design
HA method for Trunk Roads & Motorways
Includes long-life designs (> 80 msa)
40 year design life (can be 20 years) Semi-empirical (analytical alternatives
allowed) Divided into foundation design and upper
pavement design
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Foundation design
Where does the foundation start?
Upperpavement
Pavement
foundation
SurfacingUpper Base
Lower Base
Subbase
Capping
Subgrade
HD26
HD25
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Philosophy
Based around the concept of a Surface
Modulus (half-space)
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Foundation classes
Class 1 50MPa Capping Only (< 20 msa)
Class 2 100MPa Granular Subbase (< 80 msa)
Class 3 200MPa Weak Cemented Subbase
(including hydraulically bound)
Class 4 400MPa Strong Cemented Subbase
(including hydraulically bound)
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HD25
Standard DesignsStandard Designs for Classes 2 and 3 (+
Class 1 for non HA roads); restrictedchoice of materials; CONSERVATIVE
Performance DesignsPerformance Designs for Classes 1 to 4;very wide choice of materials; much more
testing specified; MORE REALISTIC
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0
100
200
300
400
500
600
700
0 50 100 150
Subgrade Stiffness Modulus (MPa)
Th
ickness(m
m)
Capping, MCHW1 Series 600
Total Foundat ion thickness, Subbase Types 1,
2, 3 and R
Total Foundat ion thickness, Subbase Types
CBGMA or CBGMB, C3/4 or C5/6
CBR (%)
2 3 5 8 10 12 15 20 25
Class 2
Standard Class 2
(100MPa)
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Performance designs
Basis of Designs:
Three criteria
Surface deflection(relates to Surface
Modulus)
Subgrade Strain(relates to rutting)
Practical minimumthicknesses
40kN
Subbase
Capping
Subgrade
Surface
deflection
Subgrade
strain
10000MPa layer assumed 1.5m below
surface of subgrade
Circularcontact area,
radius 151mm
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Performance Class 2
(100MPa)
0
100
200
300
400
500
0 50 100 150Subgrade Stiffness Modulus (MPa)
SubbaseThickness(mm)
E(subbase) = 150MPa
E(subbase) = 200MPa
E(subbase) = 250MPa
Class 2
CBR (%)
2 3 5 8 10 12 15 20 25
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Performance Class 3
(200MPa)
0
100
200
300
400
500
0 50 100 150Subgrade Stiffness Modulus (MPa)
SubbaseThickness(mm)
E(subbase) = 500MPa
E(subbase) = 750MPa
E(subbase) = 1000MPa
E(subbase) = 2000MPa
Class 3
CBR (%)
2 3 5 8 10 12 15 20 25
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Stiffness measurement
Table 3.1 Equilibrium Subgrade CBR Estimation
High Water Table Low Water Table
Poor
ConstructionConditions
Average
ConstructionConditions
Good
ConstructionConditions
Poor
ConstructionConditions
Average
ConstructionConditions
Good
ConstructionConditions
Soil PI
(%)
Thin Thick Thin Thick Thin Thick Thin Thick Thin Thick Thin Thick
Heavy Clay
Silty Clay
Sandy Clay
70
60
50
40
30
20
10
1.5
1.5
1.5
2
2.52.5
1.5
2
2
2
2.5
3.54
3.5
2
2
2
2.5
34
3
2
2
2.5
3
45
6
2
2
2
2.5
3.54.5
3.5
2
2.5
2.5
3
57
7
1.5
1.5
2
2.5
33
2.5
2
2
2
2.5
3.54
4
2
2
2
3
45
4.5
2
2
2.5
3
46
7
2
2
2
3
4
6
6
2.5
2.5
2.5
3.5
6
8
>8
Silt* - 1 1 1 1 2 2 1 1 2 2 2 2
Sand (poorly
graded)
Sand (well
graded)
Sandy Gravel
(well graded)
-
-
-
------------------------------------------------------------20------------------------------------------------------------
------------------------------------------------------------40------------------------------------------------------------
------------------------------------------------------------60------------------------------------------------------------
* estimated assuming some probability of material saturating
CBR
DCP
Springbox
Chart
FWD
Plate Loading
Triaxial
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Other layer combinations
Any combination of layers possible
The designer has to carry out a Multi-Layer Linear Elastic analysis to ensure
that the criteria are all satisfied Surface deflection
Subgrade strain Practical minimum thickness
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Outline
Standard UK pavement design
Foundation Upper pavement
Long Term Pavement Performance Model(LTPPM)
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Background
LTPPM developed with University of
Cambridge (Cebon)
Similar concept to MMOPP (Ullidtz)
Flexible (asphalt) pavements
Deterministic iterative procedure (profile &damage tracking)
Aggregate damage type of approach
V hi l
V hi l
V hi l
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LTPPM
Dynamicvehicle/axlegroup models
Primaryresponsecalculation
Damagecalculation
Feedbackmechanisms
Tyre forces
Time
Forc
e
Vehicle
simulation
Theoretical road damage
Distance along road
Damage
Road damage model
Lo g N
Log
Materialproperties
Time
Strain
Road strain at each point
Road model
Road response calculation
Distance
Strain
Influence
function
Environment
static
Surfaceruttingfedbackintovehiclemodel
Fatigue
damagefedbackinto
primaryresponsemo
del
Tyre forces
Time
Forc
e
Vehicle
simulation
Theoretical road damage
Distance along road
Damage
Road damage model
Lo g N
Log
Materialproperties
Time
Strain
Road strain at each point
Road model
Road response calculation
Distance
Strain
Influence
function
Environment
static
Surfaceruttingfedbackintovehiclemodel
Fatigue
damagefedbackinto
primaryresponsemo
del
Tyre forces
Time
Forc
e
Vehicle
simulation
Theoretical road damage
Distance along road
Damage
Road damage model
Lo g N
Log
Materialproperties
Time
Strain
Road strain at each point
Road model
Road response calculation
Distance
Strain
Influence
function
Environment
static
Surfaceruttingfedbackintovehiclemodel
Fatigue
damagefedbackinto
primaryresponsemo
del
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Example
Effect of road friendly suspensions
2 classes of pavement simulated
Major road (350mm asphalt)
Minor road (125mm asphalt)
Typical 3 layer flexible pavement structure
4oC to 18oC variation in MMAT
S rface profile e ol tion
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Surface profile evolution
(Major road)
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0 10 20 30 40 50 60 70 80 90 100
Distance / m
SurfacePro
fileElevation
/m
36 million load passes(10 years)
72 million load passes(20 years)
Initial profile
Rutting evolution
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Rutting evolution(Major road)
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60 70 80
Load Passes (Million)
AverageR
utDepth/mm
'Critical' rut depth
Steel fleetRoad friendly fleet
20 years
Fatigue evolution
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Fatigue evolution(Major road)
0
0.5
1
1.5
2
2.5
3
3.5x10-3
0 10 20 30 40 50 60 70 80
Load Passes (Million)
95th
PercentileFatigueDamage
Steel fleet
Road friendly fleet
20 years
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Fatigue evolution
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Fatigue evolution(Minor road)
Steel fleet
Road friendly fleet
20 years
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2
Load Passes (Million)
9
5thPercentile
FatigueDam
age
'Critical' fatigue damage
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Predictions
% increase in life changing from steel to
road friendly (air) suspensions
Major Minor
EC 24% 42%
LTPPM (3.5) 3% 39%
LTPPM (1) 0% 90%
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Outline
Standard UK pavement design
Foundation Upper pavement
Long Term Pavement Performance Model(LTPPM)
Summary
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Summary UK design
Foundation design + upper pavement
design
4 performance levels (surface modulus)
for foundations
More flexible designs (wider range of
materials)
Performance designs allowed
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Summary LTPPM (2)
Different modes of deterioration predicted
for different classes of pavement
Changing from steel to air increases life of
major road by
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Pavement design in the UKand future developments
Andy CollopProfessor of Civil EngineeringDirector of NTEC