ted james components for ire pavements november 2012
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DESIGN METHODDEFICIENCIES IN
INDONESIA
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AASHTO
STRENGTH: widely understood in Indonesia
WEAKNESSES:
4th power rule (overloading not fully corrected)
concrete pavement solutions too thin because 4th powerunderestimates concrete damage from overload
Simplistic layer coefficient + m value approach topavement materials behaviour
Multi layer analysis often forgotten (allowing inappropriatelayer thicknesses)
Poor on soft soil subgrade analysis
Judgement based rehabilitation layer coefficients
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AUSTROADS
STRENGTH:
A mechanistic design method
5th power rule
Easier to model special materials (modified bitumen)
Comprehensive modelling of temperature effects
Mechanistic granular materials behaviour
Based on PCA concrete design more responsive to overloading
WEAKNESSES:
Poor on soft soil subgrade analysis
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DGH 2012
Retains DGH 2002, 2003 and 2005 as design basis
Chart based
Incorporates Austroads features including
5th
and 7th
power Mechanistic design model
Overlay and recycling model
Foundation design section for Indonesian conditions
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DGH
Pavement Design Guideline 2012foundation design principles
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Indonesian designers and contractors have a bad habit of
assuming that typical Indonesian subgrades are CBR 6%
They are rarely that strong 2.5 to 4% is more typical
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Better foundation design is needed
Austroads presumptive CBRs can be too high for Indonesiaswet climate
A statistical approach to subgrade strength is needed
If the subgrade can not be dried to optimum it cannot becompacted . Therefore the laboratory CBR is irrelevant(Pantura)
If a saturated soft soil exists beneath a low embankment(Pantura), the subgrade must be modeled as a two layersystem
Dry soft soils may have low density to a considerable depthand therefore cannot be compacted by normal means thepresence of low strength layers must be considered
DGH 2012 tries to deal with these issues
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Characteristic CBR by soil type
The UK uses lower presumptive CBR values than Australia. WHY
I THINK BECAUSE THE UK WETTER CLIMATE MEANS THAT
SUBGRADE PREPARATION AND COMPACTION CAN NEVER BE
PERFECTS. THE USA AND AUSTRALIA WITH DRIER CLIMATESTHAN INDONESIA, AND GENERALLY BETTER GROUND
CONDITIONS, CAN ACHIEVE OPTIMUM MOISTURE AND FULL
COMPACTION IN SUBGRADES, INDONESIA AND THE UK DO
NOT.
DGH 2012 INCLUDES CHART 8.1 FOR PRESUMPTIVE CBRVALUES IN WET CLIMATES
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Capping layers on soft soil
DGH 2012 require up to 1200 mm
A successful flexible pavement on soft soil (Pantura:
Lohbener Jatibarang 2006, cap 1.2, total embankment
2.2 m
4 failed concrete pavements used total embankments of
1.5 m app and capping layers of 1.1 m
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The DGH 2012 guideline requires the characteristic CBR to
be determined:
Characteristic = mean 1.3xstandard deviation
Heavilly loaded roads (esa > 107) need test pit based
rehabilitation analysis deflection data is not enough
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Original ground and subgrade
characteristic strengths
If the soil can be compacted laboratory CBR results apply
If compaction is not possible ie saturated soft soils insitustrength data must be used Lab CBRs are irrelevant.
If a new alignment or widening is located on deep normally
consolidated soft soil the insitu bearing capacity, soft layerdepth and consolidation parameters must be determined
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PANTURA
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PANTURA foundations
The existing road embankment overlays a normally
consolidated saturated silty clay soft soil platform
Often the embankment is only 1 to 1.5 meters
New flexible pavement on 2 metre embankments has
bee successful (JatibarangLohbener HLRIP II, PM Ir
Juliansyah (2006)
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Concrete on 1.5 m embankments on soft soil has a history
of severe cracking in Java
These pavements commonly have a soft soil platform CBR
2 2.5% at about 1.5 meters below the surface (IndII
activity 201 finding)
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Some causes of concrete cracking
on soft soil
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Concrete cracking on soft soil
four factors :
Differential settlement
Effective subgrade strength
Deflection of the soft soil zone under dynamic
loading
Poor construction quality
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Differential settlement limits for jointed plain
concrete from an unpublished report
20mm lifetime differential
settlement in 30m
deflection bowl will causecracking. Differential
settlement = approx 0.5 x
total settlement (general
case) or
= total settlement at
structure abutment
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safe settlement for PANTURA soft after
construction including secondary (mm)(preload new alignments)
Near structures other
Plain doweledconcrete
Not applicableuse reinforced or
flexible
40
Reinforced
doweled concrete
30 100
Flexible pavement 30 (riding quality) 100
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Limiting differential settlement in soft soil
areas by preload (= capping layer possibly plussurcharge)
Preload times for plain doweled concrete might be 4 to
18 months
Can be reduced by wick draining or vacuum
Therefore usually only new alignments can
be pre consolidated
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When to reinforce concrete base
Differential movement exceeds table values
Adjacent to structures
Odd shaped slabs
Minimum capping layer thickness cannot be
provided (existing Pantura)
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Effective subgrade CBR for rigid
pavement on soft soil
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Consider a Pantura rigid pavement
foundation analysed mechanistically
Original ground saturated silty clay
CBR 2.5%
Embankment or cappingCBR 5%
Granular CBR 15% effective
LMC
Concrete base
1
520mm
Compare stress
level between
illustrated subgrade
and an infinitely
uniform subgrade
Calculateequivalent infinite
subgrade CBR at
top of
embankment
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horizontal
stress in
concrete
base
Depth of capping layer (mm)
over a BR 2.5 soft soil zone
equivalent CBR at top of
capping layer (%) (an infinite
subgrade with uniform CBR
0.35
0.37
0.39
0.41
0.43
0.45
0.47
750 950 1150 1350 1550
Series1
0.35
0.37
0.39
0.41
0.43
0.45
0.47
2 2.5 3 3.5 4 4.5 5 5.5 6 6.5
Mechanistic analysis of capped soft soil
subgrade CBR for case with CBR 2 platform
1500 mm below surface
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Conclusion:
standard methods for subgrade analysis generally look at
the top meter of the subgrade. They can over estimate the
effective CBR if there is a low strength platform at depth.
The plate bearing test also over estimates slightly
The effective CBR is only 3.5 to 4% on top of a typicalcapping layer
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Deformation under dynamic loading
(Pumping) of soft soils
both flexible and rigid pavements pump on low
embankments on Pantura soft soil
A total embankment of over 2 m seems to be necessary to
stop pumping.
Standard subgrade design does not address this failure
mode
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Finnish research shows that deformation under dynamic
loading is strongly correlated with the ratio of live load toconsolidation pressure
This ratio is very small for normal pavements oncompacted soils but high for low embankments on softsoil
Current design rules do not recognise this distinction
In geotechnical terms the soft soil cycles under dynamicwheel loads on the reconsolidation line. When it cyclesover a wide range the foundation is said to pump
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I think this live load movement effect is a main cause ofexisting Pantura alignments reconstructed pavementcracking since the embankments loading pressure does
not change much with reconstruction
Pumping would not be an issue on 1.5 meter embankmentsif vehicles were legally loaded.
Overloaded vehicles I think need a 2 m embankment heightto stop pumping whereas at least for rigid pavementlower embankments address standard structural issuessufficiently
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CONCLUSIONS: Heavily trafficked
flexible pavements on soft soil
a minimum embankment / pavement layer structure of
about 2 meters may be necessary to limit subgrade
deflection under Indonesian axle loads for both flexible
and rigid pavement
The effective top of capping layer, subgrade CBR under a
rigid pavement is about 3.5% for a capping layer CBR of
5%
If differential settlement limits can not be achieved,
reinforced concrete bases or flexible pavement must be
used.
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CONCLUSIONS: Heavily trafficked
flexible pavements on soft soil (continued)
Since preloading or grade raising options for existing
Pantura pavements is limited, rehabilitation solutions must
use reinforced concrete. Worst cases may also requiremicro piling, cakur ayam or other
New alignments on soft soil require preloading, wick
draining or vacuum treatment
Research is needed
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