S TRUCTURE WITH A C RUSHED S TONE O VERLAYING ON AN E XISTING T HICK A SPHALT L AYER JP Maree Stellenbosch University Student V3 Consulting Engineers Prof K Jenkins Stellenbosch University ID: 627158
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Slide1
A
NALYSING A
P
AVEMENT
S
TRUCTURE WITH A
C
RUSHED
S
TONE
O
VERLAYING ON AN
E
XISTING
T
HICK
A
SPHALT
L
AYER
JP Maree: Stellenbosch University: Student (V3 Consulting Engineers)
Prof. K Jenkins: Stellenbosch University:
SANRAL
Chair in Pavement Engineering
S Bredenhann:
SANRAL
Prof. A Molenaar: Delft University of Technology, the NetherlandsSlide2
CONCLUSIONS AND RECOMMENDATIONS
INTRODUCTION
INDEX
CASE STUDY
THEORETICAL ANALYSES OF PAVEMENT
PAVEMENT STRUCTURAL BEARING CAPACITYSlide3
Older granular subbase and selected layers
I
NTRODUCTION
Inverted pavement structure
Conventional
vs
Study
Surfacing
Unbound granular Base
Bound (stabilised) Subbase
Unbound gravel Selected layer
Unbound gravel Selected layer
Asphalt surfacing
Crushed stone base
Older thick asphalt layer Slide4
I
NTRODUCTION
Fundamental questions generated from an engineering perspective:
What will the advantages be?
Why is this rehabilitation option not more popular?
Will there be economical benefits?
What are the risks associated, such as:
Could water be trapped at the interface?
Could compaction be a problem?
Could slip occur at the interface, and what would this lead to?
To answer some of these questions, the inverted pavement structure was analysedSlide5
C
ASE
S
TUDY (NATIONAL ROUTE N1 SECTION 17)
Older granular subbase and selected layers
±50mm Asphalt surfacing
±130mm Crushed stone base
±200mm Older thick asphalt layer
Info from test pits
Ventersburg
KroonstadSlide6
C
ASE
S
TUDY (NATIONAL ROUTE N1 SECTION 17)
Pavement history:
Was constructed in 1989, carried approximately 18 MESA and is currently under reconstruction.
Pavement analysis:
The
FWD
measurements indicated the road is still in a
sound
condition
Back-calculation provided unrealistic results and were discarded
IRI
measurements were within the
warning
category
The majority of measured ruts were less than 10mm, however...Slide7
C
ASE
S
TUDY (NATIONAL ROUTE N1 SECTION 17)
Shoving was witnessed in the outer wheel path: Slide8
T
HEORETICAL ANALYSES OF PAVEMENT
The methods used:
Stress-dependency method
Linear Elastic Analysis (LEA)
Finite Element Analysis (
FEA
) Slide9
T
HEORETICAL ANALYSES OF PAVEMENT
Stress-dependency analysis of the slip:
FWD
back-calculation
→
unrealistic
→
discarded
Stress-dependency method
Bulk-stress log-log model
Calculated in
mePADS
Three pavement structures (from the case study) were used in the calculations:
(base) Slide10
T
HEORETICAL ANALYSES OF PAVEMENT
Stress-dependency analysis of the slip:
The aim was to determine the modulus of the base
The modulus of the asphalt was unknown
→
chose a lower and upper limit (1500 MPa – 5000 MPa)
All models showed a significant reduction in base moduli when slip were introduced
The reduction in modulus is a function of the old asphalt modulus and combined thickness of the base and the old asphaltSlide11
T
HEORETICAL ANALYSES OF PAVEMENT
Stress-dependency analysis of the slip:Slide12
T
HEORETICAL ANALYSES OF PAVEMENT
The influence of slip on the surface deflection (LEA)
Three case study models were evaluated in
mePADS
The maximum deflections were measured:
Increased by 45%
Increased by 45%
Increased by 38%Slide13
T
HEORETICAL ANALYSES OF PAVEMENT
Finite Element Analysis (
FEA
) with slip
Slide14
T
HEORETICAL ANALYSES OF PAVEMENT
Finite Element Analysis (
FEA
) with slip
Drawbacks:
Homogenous-isotropic-linear-elastic
Static loading
Y
X
ZSlide15
T
HEORETICAL ANALYSES OF PAVEMENT
Finite Element Analysis (
FEA
) with slip
Full slip between Base layers and Older Asphalt layer
Slip Surface
No slip between Base layers and Older Asphalt layer
Slip Surface
Horizontal displacement Slide16
T
HEORETICAL ANALYSES OF PAVEMENT
Finite Element Analysis (
FEA
) with slip
Maximum slip distance
All models showed tensile stresses in the base of more than 50 kPa, this was deemed unrealistic and was adjusted
Model
Maximum slip horizontal distance
Distance of maximum slip from centre
N1-17_11.8
41 µm
200 mm
N1-17_25.6
44 µm
200 mm
N1-17_36.4
51 µm
200 mmSlide17
T
HEORETICAL ANALYSES OF PAVEMENT
Finite Element Analysis (
FEA
) with slip Slide18
T
HEORETICAL ANALYSES OF PAVEMENT
Finite Element Analysis (
FEA
) with slip Slide19
P
AVEMENT STRUCTURAL BEARING CAPACITY
Three methods were:
Pavement Number (
PN
) method
Linear elastic analysis (LEA) with
mePADS
Finite element analysis (
FEA
) in
Abaqus
& SA transfer functions
Results from analyses:
All models with no slip were able to carry the historical traffic loading
Full slip
→
up to 90% reduction in bearing capacity
→
base is critical layer
The bearing capacity of the pavement is very sensitive to slip
Possible that a partial or full bond was created between the base and older asphalt, as the road carried traffic successfully for 24 years Slide20
C
ONCLUSIONS AND RECOMMENDATIONS
Conclusions:
Case study:
Mechanical measurements showed that the pavement is in a good condition and severe shoving in outer wheel track was witnessed.
Linear elastic analysis:
Showed significant reduction in base modulus when slip was introduced and the surface deflection increased exponentially when slip increased
Finite element analysis:
When slip was introduced the stresses and strains increased in the base and decreased in the older asphalt layer
Bearing capacity analysis:
Pavement could carry traffic loading without slip, but could not carry the traffic loading with slip (90% reduction), therefore it is very sensitive to slip
A bond was possibly created between the base and the older asphalt layer
A high level economic analysis found that this pavement is the cheapest, even with 10% repairs to the old asphalt layer
Based on the results of this study, the inverted pavement structure may be considered a viable construction method for rehabilitation of an existing road structure
Slide21
C
ONCLUSIONS AND RECOMMENDATIONS
Recommendations:
FEA
modelling:
Apply a dynamic load
Limit the tensile stresses in the granular materials to 50kPa
Add stress-dependency properties to the material
Carry out a construction energy analysis and emission analysis to determine if this pavement structure is a more sustainable solution
Determine the risk of the inverted pavement structure in terms of maintenance and performance due to ingress of surface water
Analyse more studies of such inverted pavement structures to confirm their feasibility as an alternative pavement rehabilitation/strengthening option Slide22
END
QUESTIONS?