Ted James components for IRE Pavements November 2012

7/29/2019 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

Documents

Ted James components for IRE Pavements November 2012