03 LVSR Wshop Mali Jan'06 MatrPvmentDesign MPinard

8/12/2019 03 LVSR Wshop Mali Jan'06 MatrPvmentDesign MPinard

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Alternative Materials and Pavement Design TechnologiesAlternative Materials and Pavement Design Technologies

for Lowfor Low--Volume Sealed Roads + Case StudiesVolume Sealed Roads + Case Studies

Mike PinardWorld Bank Consultant

[email protected]

Internat ional Work shop , Bamako, MaliInternat ional Work shop , Bamako, Mal i

18th18th 19th J anuary 200619th January 2006


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Outline of Presentation

Introduction Materials Issues

Pavement design issues

Other issues


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Pavement design and materials

Pavement structure terms


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Examples

Challenge of Using Natural Gravels Materials typically make up 70% of total cost of LVSR

90% of problems occurring on LVSRs are materials related

Overwhelming need to be knowledgeable about use of local materials

Tend to be variable and moisture sensitive require use of appropriate designs,construction techniques and drainage measures

Standard methods of test (e.g. CBR) often do not provide true assessment of performance

Conventional specs apply to ideal materials and preclude use of many natural gravels(grading, plasticity, strength)

Local road building materials often non-standardcompared with temperateclimate materials. Disparagingly referred to as marginal, low cost, etc.

Regional research work has allowed revised specs to be derived for major groups ofnatural gravel materials found in region.


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Examples

Materials Options

Crushed limestone

CalcreteLaterite

As-dug, nodular laterite


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The chal lenge

Existing pavement design methods cater to relativelyhigh volumes of traffic with damaging effect quantified interms of esa. In contrast, main factors controllingdeterioration of LVRs are dominated by the local roadenvironm ent and detai ls of design (drainage),con struct ion and maintenance pract ice.

Conventional specs apply to ideal materials

Standard methods of test do not always give a trueassessment of performance of local materials


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Materials and specs

Traditional specifications for basegravels typically specify a soaked

CBR @ 98% MAASHO of 80%, PI of


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Using local mater ials

The art of the roads engineer consists for a good part

in utilising specifications that will make possible the useof materials he finds in the vicinity of the road works.

Unfortunately, force of habit, inadequate specifications

and lack of initiative have suppressed the use of localmatereials and innovative construction technologies

Consider materials fitness for purpose

Make specification fit materials rather than materialsfit specification (resource based specs)


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Outputof SADC research work

Extensive research h as been

und ertaken in the SADC

region o ver the past 20 30

years. This has enabled local,

non-standard mater ia ls to

be successfu l ly inc orporated

in approp r iate pavement

design s for LVSRs.

The minimum standard of 80 per cent soakedCBR for natural gravel bases is inappropriatelyhigh for many LVSRs. New l imits are

recommended depending on traf f ic , mater ials andcl imate.

The grading envelopes for natural gravel basesare too narrow. Alternative (wider) envelopes arerecommended for relat ively l ight ly traf f icked roads

Traffic below 300,000 to 500,000 esa was not asignificant factor on pavement deterioration. Manyroad sections performed well even whensubjected to a high degree of overloading and withPIs up to 18. New l imi ts for PI are recommended.

Drainage was a significant factor onperformance, even in dry areas. A min imum crownheight of 0.75 m is recommended


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CBR versus stiffness


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Compaction/density/permeability

No. of roller passes

Density/Stiffness

Plastic Elasto-plastic ElasticA B C

I I

D2 I

ID1

N1

N2

Compaction to refusal


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Stiffness versus density


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Benefits of Compaction to Refusal

M

axAnnualDeflection(mm)

Pavement Life (E80s)

Increase in life

Reduction in deflection

deflection/life relationship


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Pavement material characteristics Material strength derivedfrom combination of:

- cohesive effects- soil suction- physio-chemical (stab) forces- inter-particle friction

Material selection influencedby:

- traffic loading- environment- material properties (plasticmod)- pavement configuration


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Shear strength versus soil suction

1 2 3 4

pF

Soil suction

Soilstren

gth(CBR)

75

50

25

Soaked

Optimum moisture content

Equilibrium moisture content


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Pavement design methods Should be based on experience, theory structural and materialbehaviour

Should take account of local conditions of climate, traffic, availablelocal materials, other environmental factors

sub-grade classes: wide enough to take advantage of range odstrong subgrades

Design traffic class: wide enough to cater incrementally for trafficloadings up to 0.5 m esa

Material classes: wide enough to cater for full range and differing

properties of natural gravels Materials specs should be based on proven field performance inrelation to traffic, subgrade design class, geo-climatic zone, etc


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Pavement design system

Construction and

Maintenance Factors

Traffic

Environmental

Factors

Subgrade Soils

Pavement Materials

PavementConfiguration

5.4.3 - INPUT VARIABLES

Structural Design

Cost Comparisons Selected Design

5.4.4 - DESIGN PROCESS 5.4.5 - DESIGN OUTPUT

External Factors

(Chapter 3)

Implementation

Pavement design system


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Pavement design methods

Mechanistic-EmpiricalMethods

S-N Method (1993)

TRH4 (1996)

Empirical Methods

DCP Method SATCC Pavement Design

Guide (1997)

TRL/SADC Pavement Design

Guide (1999)

Country-specific: Zimbabwe Pavement Design Guide (1975)

Botswana Roads Design Manual(1982)

Tanzania Pavement and Materials Design Manual (1999)

South African Provincial Design Guides


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Traffic characteristics

Most design methods used in SADC region cater for relatively high volumes of traffic, typically inexcess of 0.5 million ESAsover a 1015 year design life with attention focused on load-associated

distress.

For large proportion of LVRs in the region, carrying < 0.30 million ESAsover their design life,priority attention should be focused on ameliorating effects of the environment, particularly rainfalland temperature, on their performance


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Moistu re effec ts

Control of moisture is single

most important factor controllingperformance of LVSRs

Appropriate pavementconfiguration is critical forcontrolling moisture

Factors to be consideredinclude:

shoulders permeability inversion internal, external drainage

Moisture movements

Moisture zones in a LVSR


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Pavement con f igu rat ion Pavement configurationinfluenced by materials propertiesand influence of water on their

properties Attention to detail in drainagedesign and construction isessential for optimumperformance

Essential to avoid permeabi l i tyinvers ion


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Examples

LVSR Pavements (ideal cross-section)

Crown height: Crown height is a critical

parameter that correlates well

with the actual service life of

pavements constructed from

natural gravels ( d 0.75 m)

Sealed shoulders reduce/

eliminate lateral moisture

penetration under carriageway

Avoiding permeabilityinversion facilittes good

internal drainage

d (m)

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Typical specifications

150 mm natural gravel G4 base

compacted to refusal (100% Mod. AASHTO)

150 mm natural gravel G5 subbase

compacted to refusal (100% Mod AASHTO?)

150 mm natural gravel G6 USSG

compacted to refusal (100% Mod AASHTO?)

150 mm natural gravel G7 LSSG

compacted to refusal (100% Mod AASHTO)

Fill, where necessary, at least G10

compacted to refusal (100% Mod AASHTO)

19 mm max. size Ott a seal surfacing

with sand/crusher dust cover seal

150 mm crushed stone base

compacted to 98% Mod AASHTO

150 mm natural gravel G5 subbase


150 mm natural gravel G6 USSG


150 mm natural gravel G7 LSSG

compacted t o 93% Mod AASHTO

Fill, where necessary, at least G10


19/9.5 mm max. size double

surface treatment

Traditional New

Life cycle cost ratio

1.0 1.3 to 1.5


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Benefits of Adopting Recommendations

Reduced surfacing costs whilst maintaining year round

access.

Using seals as a spot improvement measure.

Lower economic/financial costs for specific tasks. Increasing the use of labour and local resources where

appropriate.

Reduced haulage distances, reduced processing costs. Adopting appropriate surfacing technologies such as

sand seals and Ottaseals.

Increased density, reduced road deterioration andincreased maintenance intervals.

Compacting pavement layers to refusal, where feasible,rather than to arbitrary prescribed levels.

Reduced haulage distances and materials costs. Utilising an existing gravel wearing course e.g. as base

or sub-base .

Reduced pavement costs due to lesser haulage

distances and reduced materials processing costs.

Use of more appropriate pavement designs and natural

gravel rather than crushed stone.

Reduced earth works and environmental damage. Replacing a conventional geometric design process by a

design by eye approach, where appropriate

Potential BenefitsOption


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Life cycle cost analysis

RM RM RM RM

ST ST

RV

PC

OV

Analysis Period

Structural Deign PeriodKey:

PC = Initial Pavement Construction

RM = Routine Maintenance

ST = Surface Treatment

RV = Residual Value

OV = Overlay

Time (Years)

Co

stsduringlifecycle

Initial Average Daily Traffic (vpd)

NPVofUpg

radingInvestment($

)

0

Revised approaches

75+

vpd

Traditional approaches

250+

vpd

Components of a Life Cycle Costing

Break-even trafficTraditional vs revised approaches


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Pavement Design Philosophy

0

20

40

60

80

100

1997 2002 2007 2012 2017

Year

Road

Conditi Good

Fair

Poor

Very Poor

Maintenance Actions

No Maintenance

Moisture Ingress

(Typically Designed for Traffic Expected over 15 - 20 Years)


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Cost of Maintenence Delay

3-5 Years

5-8 Years

Repair Cost = R 0,1mill / km

0

20

40

60

80

100

2005 2010 2015 2020 2025

Year

Road

Co

nditi

Good

Fair

Poor

Very Poor

3-5 Years


5-8 Years


(Ratio 1:6)

Ratio 1:18


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Cost of Maintenence Delay


0

20

40

60

80

100

2005 2010 2015 2020 2025

Year

Road

Conditi Good

Fair

Poor

Very Poor

3-5 Years


5-8 Years


(Ratio 1:6)

Ratio 1:18


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Examples

Overloading

Axles of evil


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Examples

Impact of Overloading on Pavements


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Examples

Impact on Pavements

Pavement performanceunder legal load limits

Pavement performance

under overloading


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Examples

Cost of Overloading

Botswana 2004: US $2.6 million

South Africa 2002: US $100 million

Sub-Saharan Africa 2004:US $500 million

E l


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Examples

Developments in Overload Control

Mandatory off-loading of over-loaded vehicles

Decriminalisation of offenses for overloading by handling themadministratively and imposing a requirement on the overloader topay an overloading fee

Linking level of imposed fees for overloading with actual cost ofroad damage, i.e. by imposing economic fees

Outsourcing weighbridge operations to the private sector on aconcession basis, i.e. embarking on a commercialised

public/private sector approach to overload control

E amples


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Examples

Modern Weighbridge Equipment


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Examples

Environmental issues borrow pits

Children exposed to risk of drowning and poor quality water

Ponding increases level of mosquito-borne disease

Typical, un-renovated borrow-pit in the SADC region

Introduction ofTechnical Audits at

Feasibility Stage


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Examples

Environmental issues borrow pit restorationBefore

After


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The Final Result A Meeting of Minds


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The Final Result

The successful engineering of a low volum e sealed road requires ingenui ty , imaginat ion and in novat ion. I t entai ls

wor k ing w i th nature and using loc al ly available, non -standard materia ls and other resources in an opt im al and

envi ronm ental ly sustainable manner.

It wi l l rely on planning , design, construct ion and m aintenance techniques that m aximize the involvement of lo cal

comm uni t ies and con t rac tors .

When prop erly engineered to an approp riate standard, a LVSR wi l l reduce transport cos ts and faci li tate socio-

econom ic growth and d evelopm ent and reduce poverty in the SADC region.


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FinallyFinally

Our VisionOur Vision

It is not wealth which makes good roads possible

but, rather, good roads which make wealth possible

Adam Smith


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Thank you

Documents

03 LVSR Wshop Mali Jan'06 MatrPvmentDesign MPinard