icao doc 9157 part 3

4 I C A O 9357 P A R T * 3 t* = 4843416 0039364 477 m

DOC 9157-ARf901 P a r t 3 Amendment Bo . 2 31/8/89

AMENDMENT NO. 2

TO TBE

AERODROME DESIGN MANUAL

PART 3

PAVEMENTS

SECOND EDITION - 1983

Amendmen No, 2 includes guidance material on grooving runway in t e r sec t ions and the cons t ruc t im of asphal t ic over lays . Also inc luded are updated data. an ACRs f o r a i r c r a f t .

Replace exis t ing pages Cvii), 3--219 t o 3-224, 3-237 t o 3-249 and 3-339 t o 3-346 by the a t tached new pages.

Remove exiatfng pages 3-347 and 3-348.

Recora the entry of t h i s amendment on page (ii).

1.

2.

3 .

5 .

Transmittal Note

DOC 9157-Ah/901 P a r t 3

Amendment No. 1 25/10/85

AMENDMENT No. 1

TO THE

AERODROME DESIGN MANUAL

PART 3

PAVEMENTS

Second Edi t ion - 1983

1. The purpose of t h i s amendment i s to update the computer programmes, f o r t h e determinat ion of ACNs and t o i n c o r p o r a t e d a t a i n r e s p e c t of s eve ra l new a i r c r a f t t y p e s .

2 . P lease rep lace the ex is t ing pages by the a t tached corresponding new pages.

3. Remove pages 3-291to 3-298 which have been de le t ed by t h i s amendment.

4 . Record en t ry o f Amendment No. 1, dated 25/10/85, on page ( i i ) .

ICAO 9357 P A R T S 3 ** W 4 8 4 3 4 3 6 0039366 2LJT

DOC 9157-AN/901

AERODROME DESIGN

MANUAL

PART 3

PAVEMENTS SECOND EDITION - 1983

Approved by the Secretav General and published under his authority

IkTERhATIOhAL CIVIL AVIATION ORGAhIZATlObi

ICAO 9157 P A R T * 3 t* = 4B4L4Lb 0039367 L B b

Published in separate English, French, Russian and Spanish editions by the lnternational Civil Aviation Organization. All correspondence, except orders and subscriptions, should be addressed to the Secretary General.

Orders for this publication should be sent to one of the following addresses, together with the appropriate remittance (by bank draft or post office money order) in U.S. dollars or the currency of the country in which the order is placed.

Document Sales Unit International Civil Aviation Organization 1000 Sherbrooke Street West, Suite 400 Montreal, Quebec Canada H3A 2R2

Argentina. El Ateneo, Pedro Garcia S.A.L.E. e I., Dpto. Compras - Irnportacibn, Egypt. ICAO Representative, Middle East and Eastern African Office,

France. Representant de IOACI, Bureau Europe, 36is, villa Emile-Bergerat,

India. Oxford Book and Stationery Co., Scindia House, New Delhi

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Mexico. Representante de la OACI, Oficina Norteamerica y Caribe,

Peru. Representante de la OACI, Oficina Sudamerica, Apartado 4127, Lima 100. Senegal. Representant de IOACI, Bureau Afrique, Boite postale 2356, Dakar. Spain. Libreria de Aeroniutica y Astroniutica Sumaas, Desengaiio, 12-3-3, Madrid 13. Thailand. ICAO Representative, Asia and Pacific Office, P.O. Box 614, Bangkok. United Kingdom. Civil Aviation Authority, Printing and Publications Services,

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ICAO 9357 P A R T * 3 ** 4 8 4 3 4 3 b 0039368 032

e

Aerodrome Design Manual

(DOC 9157-AN/901)

Part 3

Pavements

Second Edition - 1983

d in the monthly supplements to the Catabgue of IC40 I44blimtkms, which holden of this publication should consult. These amendments are available free upon request.

AMENDMENTS

The issue of amendments is announced in the ICAO Bulktin a n 1

(ii)

ICAO 9157 P A R T * 3 t* YB4343b 0039370 770

FOREWORD

This revised and updated vers ion of t h e Aerodrome Design ManuaZ, Par t 3, includes guidance on t he des ign of pavements inc luding the i r charac te r i s t ics and on evalua t ion and repor t ing of t he i r bea r ing s t r eng th . The material inc luded here in i s c lose ly a s soc ia t ed w i th t he spec i f i ca t ions con ta ined in Annex 14 - Aerodromes. The main purpose o f th i s Manual i s t o encourage the un i form appl ica t ion of those spec i f ica t ions and t o p r o v i d e i n f o r m t i o n a n d g u i d a n c e t o S t a t e s . The s i g n i f i c a n t a d d i t i o n s / r e v i s i o n s t o the Manual as a r e s u l t of t h i s r e v i s i o n are:

a) background information on t h e ACN-PCN method f o r r e p o r t i n g pavement bear ing s t rength (Chapter 1);

. *

b) material on regulating overload operations (Chapter 2);

c) updated material on evaluatfon of pavements (Chapter 3) and on runway sur face t ex ture and dra inage charac te r i s t ics (Chapter 5 ) ;

d) updated material on the design-and evaluat ion of pavements provided by Canada, France, the United Kingdom andsthe United States (Chapter 4);

e) guidance on protection of asphalt pavements (Chapter 6 ) ; and

f ) material o n s t r u c t u r a l d e s i g n c o n s i d e r a t i o n s f o r c u l v e r t s a n d b r i d g e s (Chapter 7).

Chapter 4 o f t h i s Manual is based on updated material on pavement design and evaluat ion submit ted by Sta tes and i s , therefore , be l ieved to be cur ren t . Should a S t a t e , a t any time, c o n s i d e r t h a t t h e material inc luded there in i s out of date , it should inform the Secretary General o f t h i s and, i f poss ib l e , p rov ide appropr i a t e r ev i sed material.

( i i i )

ICAO 9357 PARTa3 t* 4 8 4 3 4 3 6 0039373 607 =

a TABLE OF CONTENTS

Page

Glossary ......................................................................... (ix) Chapter 1.- Procedures for Reporting Aerodrome Pavement Strength ................ 3-1

1.1 Procedure for pavements meant for heavy aircraft (ACN/PCN method) ... 3-1 1.2 Procedure for pavements meant for light aircraft .................... 3-16

Chapter 2.- Guidance on Overload Operations ..................................... 3-17 2.1 Criteria suggested in Annex 14. Attachment B ........................ 3-17 2.2 State practices ..................................................... 3-17

2.2.1 Canadian practice .......................................... 3-17 2.2.2 French practice ............................................ 3-18 2.2.3 United Kingdom practice ...................................... 3-20

Chapter 3.- Evaluation of Pavements ............................................. 3-22 3.1 General ............................................................. 3-22 3.2 Elements of pavement evaluation ..................................... 3-22 3.3 Elements of the ACN/PCN method ...................................... 3-23 3.4 Assessing the magnitude and composition of traffic .................. 3-25 3.5 Techniques for "using aircraft" evaluation ........................... 3-27 3.6 Techniques and equipment for "technical" evaluation ................. 3-31

Chapter 4.- State Practices for Design and Evaluation of Pavements .............. 3-62 4.1 Canadian practice ................................................... 3-62

4.1.1 Scope ....................................................... 3-62 4.1.2 Pavement design practices ................................... 3-64 4.1.3 Pavement evaluation practices ............................... 3-69

4.2 French practice ..................................................... 3-78 4.2.1 General ..................................................... 3-78 4.2.2 Choice of the design load ................................... 3-80 4.2.3 Designing flexible pavements ................................ 3-83 4.2.4 Designing rigid pavements ................................... 3-86 4.2.5 General design .............................................. 3-93

ICAO 7157 PART*K3 ** 4B41456 0057372 543 W

(vi> Aerodrome Design Manual

Chapter 4 ( C m t . 4.2.6 Optimized design ........................................... 3-109 4.2.7 Frost ...................................................... 3-112 4.2.8 Allowable loads ............................................ 3-114 4.2.9 Evaluation of pavements .................................... 3-120 4.2.10 Reinforcement of pavements ................................. 3-12; 4.2.11 Light pavements ............................................ 3-127

4.3 United Kingdom practice ............................................ 3-129 4.3.1 Design and evaluation of pavements ......................... 3-129 4.3.2 Reporting pavement strength ................................ 3-129

4.4 United States of America practice .................................. 3-130 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7 4.4.8 4.4.9 4.4.10 4.4.11 4.4.12

4.4.13 4.4.14 4.4.15 4.4.16 4.4.17

4.4.19 4.4.20 4.4.21 4.4.22 4.4.23 4.4.24 4.4.25 4.4.26 4.4.27

4.4.18

Introduction ............................................... Basic investigations and considerations .................... Soil tests ................................................. Unified soil classification system ......................... Soil classification examples ............................... Frost and permafrost ....................................... Soil strength tests ........................................ Pavement design philosophy ................................. Background ................................................. Aircraft considerations .................................... Determination of design aircraft ........................... Determination of equivalent annual departures by the design aircraft ..........................................

Designing the flexible pavement ............................ Critical and non-critical areas ............................ Stabilized base and sub-base ............................... Stabilized sub-base and base equivalency factors ........... Design example ............................................. Designing the rigid pavement ............................... Sub-base requirements ...................................... Critical and non-critical areas ............................ Stabilized sub-base ........................................ Design example ............................................. Optional rigid pavement design curves ...................... High traffic volumes ....................................... Reinforced concrete pavement ............................... Airport pavement overlays .................................. Pavement: evaluation ........................................

3-130 3-130 3-131 3-133 3-137 3-140 3-141 3-143 3-145 3-146 3-147

3-147 3-149 3-160 3-160 3-160 3-161 3-163 3-164 3-174 3-174 3-175 3-175 3-183 3-18 3 3-185 3-199

Chapter 5.- Methods for Improving Runway Surface Texture ....................... 3-204 5.1 Purpose ............................................................ 3-204 5.2 Basic Considerations ............................................... 3-204 5.3 Surface treatment of runways ....................................... 3-212

I C A O 9157 P A R T 8 3 ** = 4 8 4 L 4 1 b 0019373 4 8 T P a r t 3.- Pavements (vii)

Page .

Chapter 6.- Protection of Asphalt Pavements ...................................... 3-225 6.1 The problem .............................................................. 3-225 6.2 Treatment of the problem ................................................. 3-226 6.3 Protective coatings ...................................................... 3-226 6.4 Materials for protective coatings ........................................ 3-227 6.5 Application .............................................................. 3-228 6.6 Protection gained .......................................................... 3-228 6.7 Maintenance consideration ................................................ 3-229 6.8 Some related concerns .................................................... 3-229

Chapter 7.- Structural Concerns for Culverts and Bridges ......................... 3-230 7.1 Problem description ...................................................... 3-230 7.2 Types of substructures ................................................... 3-230 7.3. Some guiding concepts .................................................... 3-231 7.4 Evaluation of subsurface structures ...................................... 3-231 7.5 Considerations in design of new facilities ............................... 3-234

Chapter 8.- Construction of Asphaltic Overlays ................................... 3-237 8.1 Introduction ............................................................ 3-237 8.2 Airport authority's role ................................................ 3-237 8.3 Design considerations ................................................... 3-238B

Appendix 1 . Aircraft Characteristics Affecting Pavement Bearing Strength ....... 3-239 Appendix 2 . Procedures for Determining the Aircraft Classification Number of

an Aircraft ........................................................ 3-251 Appendix 3 . Pavement Design and Evaluation Graphs Provided by France ........... 3-299 Appendix 4 . Background Information on the United States Practice for

the Design and-Evaluation of Pavements ............................. 3-311 Appendix 5 . ACNs for Several Aircraft Types .................................... 3-339

31/8/89 No . 2 :a *:

ICAO 9357 P A R T f 3 f t 4 8 4 3 4 3 6 0039374 3Lb

GLOSSARY

Terms which are d e f i n e d i n t h e ICAO Lexicon Volume I1 (Doc 9110) are used i n accordance with the meanings and usages given therein. A wide variety of terms is i n use th roughout the wor ld to descr ibe so i l s , cons t ruc t ion materials, and components of airport pavements. A s f a r as p o s s i b l e t h e terms used i n t h i s document are those which have the widest in ternat ional use . However, for the convenience of the reader a sho r t l ist of preferred terms and secondary terms which are cons idered to be the i r equiva len t , and t h e i r d e f i n i t i o n s , i s given below.

P re fe r r ed Term Secondary Term

Aggregate

Ai rc ra f t C la s s i f i ca - t ion Number (ACN)

Asphal t ic concrete Bitumen concrete

B a s e course Base

Bear ing s t rength

CBR

Compos it e pavement

Bearing capaci ty Pavement s t r e n g t h

Cal i fornia Bearing Ra t io

Def in i t i on

General term for the minera l f ragments o r p a r t i c l e s which, through the agency of a su i tab le b inder , can be combined i n t o a s o l i d mass, e . g . , t o form a pavement.

A number e x p r e s s i n g t h e r e l a t i v e e f f e c t of a n a i r c r a f t on a pavement f o r a - spec i f ied s tandard subgrade s t rength .

A graded mixture of aggregate, and f i l l e r w i t h a s p h a l t o r bitumen, placed ho t o r co ld , and ro l l ed .

The l a y e r o r l a y e r s of s p e c i f i e d o r s e l e c t e d material of designed thickness placed on a sub-base o r subgrade to support a surface course.

The measure of the abi l i ty of a pavement t o s u s t a i n t h e a p p l i e d l o a d .

The b e a r i n g r a t i o of s o i l determined by conpar ing the pene t ra t ion load of the s o i l t o t h a t of a s tandard material (see ASTM D1883). The method covers eva lua t ion o f t he r e l a t ive qua l i t y of subgrade so i l s bu t i s a p p l i c a b l e t o sub-base and some base course materials.

A pavement cons i s t ing of b o t h f l e x i b l e and r i g id l aye r s w i th o r w i thou t s epa ra t ing g ranu la r l aye r s .

ICAO 9357 PART*3 ** W 48l l5436 0059375 252 W

( 4 Aerodrome Design ~~ Manual

Preferred Term

Flex ib le pavement

Overlay

Pavement Classif ica- t i o n Number (PCN)

Pavement s t r u c t u r e

Portland cement concrete

Rigid pavement

Sub-baae course

Subgrade

Surf ace course

Secondary Term

Pavement

Concrete

Su b+e e

Formation foundation

Wearing course

Defini t ion

A pavement s t r u c t u r e t h a t m a i n t a i n s intimate con tac t w i th and d i s t r ibu te s loads to the subgrade and depends on a g g r e g a t e i n t e r l o c k , p a r t i c l e f r i c t i o n , and cohes ion fo r s t ab i l i t y .

An addi t iona l sur face course p laced on e x i s t i n g pavement e i the r w i th o r w i th - ou t in te rmedia te base or sub-baee courses l usua l ly to s t rengthen the pavement o r r e s t o r e t h e p r o f i l e o f t h e surface.

A number express ing the bear ing s t rength o f a pavement f o r u n r e s t r i c t e d operatione.

The combination of sub-baae, baee course, and surface c~llrse placed on a s u b g r a d e t o s u p p o r t t h e t r a f f i c l o a d a n d d i s t r i b u t e i t t o t h e subgrade.

A d x t u r e of graded aggregate with Portland cement and water.

A pavement s t r u c t u r e t h a t d i e t r i b u t e e loads to the subgrade having as i t s surface course a Portland cement conc re t e s l ab o f r e l a t lve ly h igh bending res is tance.

The l a y e r o r l aye r s o f spec i f i ed s e l e c t e d material of designed thickness placed on a subgrade to support a base courae.

The upper par t of t h e s o i l , n a t u r a l o r conetructed, which supports the loads t ransmft ted by t h e pavement.

The top course of a pavement s t r u c t u r e .

J

ICAO 9357 P A R T * 3 ** 4 8 4 3 4 3 b 0039376 199

CHAPTER 1.- PROCEDURES FOR REPORTING AERODROME PAVEMENT STRENGTH

1.1 Procedure for pavements meant f o r heavy a i r c r a f t (ACN-PCN method)

1.1.1 Introduction

1.1 .1 .1 Annex 14, 2.5.2 s p e c i f i e s t h a t t h e b e a r i n g s t r e n g t h of a pavement intended f o r a i r c r a f t of mass g rea t e r t han 5 700 kg s h a l l b e made ava i l ab le u s ing t he a i r c ra f t c l a s s i f i c a t i o n number - pavement c l a s s i f i c a t i o n number (ACN-PCN) method. To f a c i l i t a t e a proper understanding and usage of the ACN-PCN method the fol lowing material explains:

a) the concept of the method; and

b) how t h e ACNs of a n a i r c r a f t are determined.

1.1.2 Concept of the ACN-PCN method

1.1 . 2.1 Annex 14 defines ACN and PCN as follows : - Am. A number expres s ing t he r e l a t ive e f f ec t of a n a i r c r a f t on a pavement

f o r a specified standard subgrade strength.

- PCN. A number express ing the bear ing s t rength o f a pavement f o r unres t r ic ted opera t ions .

A t t h e o u t s e t , i t needs t o b e n o t e d t h a t t h e ACN-PCN method i s meant only for publ ica- t i o n of pavement s t r e n g t h d a t a in the Aeronautical Information Publications (AIPs). It is not intended for design or evaluat ion of pavements, nor does i t contemplate the use of a s p e c i f i c method by the a i rpo r t au tho r i ty e i the r fo r t he des ign o r eva lua t ion of pavements. In fact, t h e ACN-PCN method does permit States to use any design/evaluation method of the i r choice . To t h i s end, t h e method shifts the emphasis from evaluation of pavements t o e v a l u a t i o n of l o a d r a t i n g of a i r c r a f t (ACN) and includes a standard proced- u re fo r eva lua t ion of t h e l o a d r a t i n g o f a i r c r a f t . The strength of a pavement i s reported under the method i n terms of the load ra t ing o f the aircraft which t h e pavement can accept on an unrestricted basis. The a i rpo r t au tho r i ty can u se any method of h i s cho ice t o de t e rmine t he l oad r a t ing o f h i s pavement. If, in the absence of technica l evaluation, he chooses to go on t he bas i s o f t he u s ing a i r c ra f t expe r i ence , t hen he would compute t h e ACN of the most cr i t ical aircraf t us ing one of the procedures described below, c o n v e r t t h i s f i g u r e i n t o a n e q u i v a l e n t PCN and publish i t in t h e A I P as t h e l o a d r a t i n g o f h i s pavement. The PCN so reported would i n d i c a t e t h a t a n a i r c r a f t with an ACN e q u a l t o o r less than tha t f igure can opera te on t h e pavement s u b j e c t t o any l i m i t a t i o n on t h e t i re pressure.

1.1.2.2 The ACN-PCN method contemplates the reporting of pavement s t rengths on a continuous scale. The lower end of the scale is zero and there is no upper end. Addi- t i o n a l l y , t h e same scale is used t o measure the l oad r a t ings of both a i rc raf t and pavements.

3-1

3-2 Aerodrome Design Manual

1.1.2.3 To f a c i l i t a t e t h e u s e of the method, a i rcraf t manufacturers will publish, i n t h e m documents d e t a i l i n g t h e c h a r a c t e r i s t f c s of t h e i r aircraft, ACTS conputed a t ~ W O different masses: maximum apron mass, and a representative operating mass empty, both on r i g i d and f l e x i b l e pavements and for the four standard subgrade strength categories. Nevertheless, for the sake of convenience Annex 14, Attachment B and Appendix 5 hereto include a t a b l e showing the ACNs of a number of a i r c r a f t . It is to be no ted tha t the mass used i n t h e ACN calculat ion is a "static" mass and that no allowance is made for an increase i n loading through dynamic e f fec ts .

1.1.2.4 The ACN-PCN method also envisages the reporting of the following information i n respect: of each pavement:

a) pavement type;

b) subgrade category;

c ) -ximum t i re pressure allowable; and

d) pavement evaluation method used.

The above d a t a are primarily intended t o enab le a i r c ra f t ope ra to r s t o de t e rndae t he permissible a i rcraf t types and operat ing masses, and the aircraft nranufacturers t o ensure compatibil i ty between a i r p o r t pavements and a i r c ra f t unde r development. There i s , hawever, no need t o r e p o r t t h e actual subgrade s t r eng th o r t he maxipaurn tire pressure allowable. Consequently, the subgrade strengths and t i r e preseures normally encountered have been grouped in to ca t egor i e s a8 i n d i c a t e d i n 1.1.3.2 belcw. It would be su f f i c i en t i f t he a i rpo r t au tho r i ty i den t i f i e s t he ca t egor i e s app ropr i a t e t o h i s pavement. (See a l s o t h e examples included under Annex 14, 2.5.6. )

1.1.3 How ACNE are determined

1.1.3.1 The flow chart, below, br ie f ly expla ins how t h e ACNs of a i r c r a f t are computed under the A W P C N method.

ACN COMPUTER * , PROGRAMME I

I I RIGID DERIVED RIGID

WHEEL CHART

RIGID PAVEMENT NOMOGRAPH$ SINGLE

m I, RIGID PAVEMENT +

Y A TABLE SHOWING ACNs OF AIRCRAFT I I I d

ACN COMPUTER * PROGRAMME 1

I 1 , I

CORPS OF ENGINEERS DERIVED FLEXIBLE k ~ i CHART

FLEXIBLE PAVEMENT PAVEMENT

- * FLEXIBLE v NOMOGRAPHS

*SINGLE WHEEL

I t i I - Y A TABLE SHOWING 3 ACNs ,OF AIRCRAFT

I C A O 9157 PARTs3 *Kt m 484141rb 0039379 9 T B m


1.1.3.2 Standard values used in t h e method and descr ip t ion of the var ious terms

a) Subgrade category. In the ACN-PCN method eight s tandard subgrade values (i .e., f o u r r i g i d p a v e m n t k va lues and fou r f l ex ib l e pavement CBR values) are used , ra ther than a continuous scale of subgrade s t rengths . The grouping of subgrades with a s tandard value a t t h e mid range of each group i s cons ide red t o be en t i r e ly adequa te fo r reporting. The subgrade s t rength categories are i d e n t i f i e d as high, medium, low a n d u l t r a low and ass igned the following numerical values:

Subgrade strength category

High s t rength; Character ized by k* = 150 MN/m3 and representing all k values above 120 ~ / I E ? f o r r i g i d pavements, and by CBB 15 and represent ing a l l CBR values above 13 f o r f l e x i b l e pavements.

Medium s t rength ; charac te r ized by k = 80 HH/m3 and representing a range i n k of 60 t o 120 MN/d f o r r i g i d pavements, and by CBB 10 and represent ing a range i n CBR of 8 t o 13 o r f l e x i b l e pavements.

Low s t rength; character ized by k = 40 MWm3 and representing a range i n k of 25 t o 60 HN/d f o r r i g i d pavements, and by CBB 6 and represent ing a range i n CBB of 4 t o 8 f o r f l e x i b l e pavements.

Ultra low s t rength ; charac te r ized by k 20 MN/rn3 and representing a l l k values below 25 MN/d f o r r i g i d pavemente, and by CBR = 3 and represent ing a l l CBB values b e l o w 4 or f l e x i b l e pavements.

b) Concrete working e t res8 for r igid pavements. For r i g i d pavements, a s t anda rd s t r e s s fo r r epor t ing pu rposes is s t i p u l a t e d (a = 2.75 MPa) only as a means of eneuring uniform reporting. The working stress t o be used for the design and/or evaluat ion of pavements has no r e l a t i o n s h i p t o t h e s t a n d a r d stress f o r r e p o r t i n g .

c) Tire pressure. The r e e v l t a of pavement research and re-evaluat ion of o l d test r e s u l t s r e a f f i r m t h a t e x c e p t f o r u n u s u a l pavement construc- t i o n (i.e., f l e x i b l e pavements with a t h i n a e p h a l t i c concre te cover o r weak upper layers) , t i re preesure effects are secondary t o load and wheel spacing, and may therefore be ca tegor ized i n four g roups for report ing purposes as: high, medium, low and very low and assigned the following numerical values:

High - No pressure lidt Medium - P r e s s u r e l i m i t e d t o 1.50 MPa Low - Pressu re l imi t ed t o 1.00 MPa Very low - Pressure l imLted to 0.50 MPa

* Values determined using a 75 cm diameter plate .

nf or tmt i on Hand1 i ng Servi ces, 2000

P a r t 3 . - Pavements 3-5

d) Mathematically derived single wheel load: The concept of a mathematically derived single wheel load has been employed i n t h e ACN-PCN method as a means to de f ine t he l and ing gea r /pavemen t i n t e r ac t ion wi thout spec i fy ing pavement thickness as an ACN parameter. This i s done by equat ing the th ickness g iven by the mathematical model f o r a n a i r c r a f t l a n d i n g g e a r t o t h e t h i c k n e s s f o r a s ingle wheel a t a s tandard t i re pressure o f 1.25 MPa. The s ingle wheel load so obtained i s then u sed w i thou t fu r the r r e f e rence t o t h i ckness ; t h i s i s so b e c a u s e t h e e s s e n t i a l s i g n i f i c a n c e i s a t t a c h e d t o t h e f a c t of having equal thicknesses, implying "same app l i ed stress t o t h e pavement", ra ther than the magni tude of the th ickness . The foregoing i s i n accord wi th the ob jec t ive o f the ACN-PCN method t o e v a l u a t e t h e r e l a t i v e l o a d i n g e f f e c t o f a n a i r c r a f t on a pavement.

e) A i r c r a f t c l a s s i f i c a t i o n number (ACN). "he ACN of a n a i r c r a f t i s numerically defined as two times the derived single wheel load, where the der ived s ing le wheel load i s expressed i n thousands of kilograms. A s noted prev ious ly , the s ing le wheel t ire p res su re i s s tandardized a t 1.25 MPa. Addi t iona l ly , the der ived s ing le wheel load i s a func t ion of the subgrade s t rength . The a i r c r a f t c l a s s i f i c a t i o n number (ACN) is def ined on ly fo r t he fou r subgrade ca t egor i e s (i.e., high, medium, low, a n d u l t r a low strength) . The "two" (2) f a c t o r i n t h e n u m e r i c a l d e f i n i t i o n o f t h e ACN is used' t o achieve. a s u i t a b l e ACN vs. gross mass scale so tha t whole number ACNs may be used with reasonable accuracy.

1.1.3.3

Because a n aircraft operates a t var ious mass and cen t re of g r a v i t y condi t ions the fol lowing convent ions have been used in ACN computa- t i o n s (see Figure 1-1).

1) t h e maximum ACN of a n a i r c r a f t i s ca l cu la t ed a t t h e mass and c.g. tha t p roduces the h ighes t main gear loading on the pavement, u s u a l l y t h e maximum ramp mass and corresponding af t c .g . The a i rcraf t tires are considered as i n f l a t e d t o t h e m a n u f a c t u r e r s recommendation f o r t h e c o n d i t i o n ;

2) relative aircraft ACN cha r t s and t ab l e s show t h e ACN as a func t ion of a i rcraf t g r o s s mass w i t h t h e a i r c r a f t c.g. a t a constant value co r re spond ing t o t he maximum ACN value (i.e., u sua l ly , t he a f t c .g . f o r max ramp mass) and a t t h e max ramp mass t ire pressure; and

3) s p e c i f i c c o n d i t i o n ACN values are those ACN va lues t ha t are a d j u s t e d f o r t h e e f f e c t s o f tire pressure and/or c .g . locat ion, a t a s p e c i f i e d g r o s s mass f o r t h e a i r c r a f t .

Abbreviations

a) Aircraf t parameters

MRGM - Maximum ramp g ross mass i n kilograms


b) Pavement and sstbgredr parePetere

Q - Standard working e t rem for reporting, 2.75 HPa t - Pavement thickneus i n centimetres

mickueso of s lab for ri@d pavemente, or

Total thickness of pav-at structural syeter burface t o subgrade) for f lcxible pave~ente (see Figure 1-21.

Figure 1-1. Landing gear loading on pavement Model DC-10 Series 30, 30CF, 40 and 40CF

Part 3.- Pavements

a 3-7

THEORETICAL ASPHALT PAVEMENT THEORETICAL CEMENT CONCRETE PAVEMENT

e

7 THICKNESS

1

Figure 1-2

k - Westergaards modulus of subgrade reaction in MN/m3 R - Westergaards radius of relative stiffness in centimetres.

This is computed using the following equation (see Figure 1-3).

E is modulus of elasticity

p is Poissons ratio (+ = 0.15) 12 (1 - p2)k

PHYSICAL MEANING OF WESTERGAARDS RADIUS OF RELATIVE STIFFNESS,L

SINGLE WHEEL LOADING ON A S L A B

, p A P P R O X l M A T E L Y \ IN SLAB

1 I 1 CONTRAFLEXURE + t L-----

I DEFLECTION . . - -. .-

- PLOT OF BENDING MOMENT

BOTTOM OF SLAB AS A (AND/OR TENSION STRESS ON

FUNCTION OF RADIAL DISTANCE FROM CENTER

L W OF LOAD)

Figure 1-3


CBR - California Bearing Ratio i n p e r c e n t

Tire Pressures

P, - Tire pressure for der ived s ing le wheel load - 1.25 MPa Pq - Tire p r e s s u r e f o r a i r c r a f t a t maximre ramp mass condition

1.1.3.4 Mathematical models. Two mathematical models are used i n t h e ACN-PCN method: the Westergaard solut ion for a loaded elastic p l a t e on a Uinkler foundation ( in t e r io r l oad case) for r i g i d pavements, and the Bouss inesq so lu t ion for s t resses and d isp lacements in a homogeneous i so t ropic e las t ic ha l f - space under sur face loading for f l e x i b l e pavements. The use of these two, widely used, models permits the maximum cor re l a t ion t o wor ldwide pavement design methodologies, with a minimra need f o r pavement paraueter values (i.e., only approximate subgrade k, o r CBR values are required) .

1.1.3.5 Computer programmes. The two computer programmes developed using these mathematical models are reproduced i n Appendix 2. The p r o g r a m f o r e v a l u a t t n g a i r c r a f t on r i g i d pavements i s based on t he p rog ram deve loped by Mr. R.G. Packard* of Portland Cement Assoc ia t ion , I l l ino is , USA and t ha t fo r eva lua t ing a i r c ra f t on f l e x i b l e pavements i s based on t h e US Army Engineer Waterways Experiment S ta t io3 Ins t ruc t ion Repor t S-77-1, ent i t led "Procedures for Development of CBR Design Curves". It may, however, be noted t h a t t h e a i r c r a f t c l a s s i f i c a t i o n t a b l e s i n c l u d e d i n Annex 14, Attachment B and in Appendix 5 of t h i s Manual completely eliminate the need to use these programmes i n r e spec t of most o f t h e a i r c r a f t c u r r e n t l y in use.

1.1.3.6 Graphical procedures. Aircraft for which pavement thickness requirement char ts have been published by the manufacturers can a lso be evaluated using the graphical procedures descr ibed below.

1.1.3.7 Rigid pavements. This procedure uses the conversion chart shown i n Figure 1-4 and t h e pavement thickness requirement charts published by t h e a i r c r a f t manufacturers. The Portland Cement Association computer programme r e f e r r e d t o i n 1.1.3.5 was used i n developing Figure 1-4. This f i g u r e relates the der ived s ingle wheel load a t a constant t i re pressure of 1.25 MPa t o a reference pavement thickness. It takes into account the four standard subgrade k values de ta i led in 1.1.3.2 a) above, and a standard concrete stress of 2.75 HPa. The f igu re a l so i nc ludes an ACN scale which permits the ACN t o be r ead d i r ec t ly . The following steps are used to determine the ACN o f an a i r c ra f t :

a) using t h e pavement requirement chart published by the manufacturer ob ta in t he r e f e rence t h i ckness fo r t he g iven a i r c ra f t mass, k value of the subgrade, and the standard concrete stress fo r r epor t ing , i.e. 2.75 MPa;

b) using the above reference thickness and Figure 1-4, obtain a der ived s ingle wheel load for the selected subgrade; and

* Refer t o document e n t i t l e d "Design of Concrete Airport Pavement" by R.G. Packard, Portland Cement Association, Skokie, I l l inois, 60076, dated 1973.

D SW L (1 000 kg)

120 t

40

t 20'

t

0 I

70

6c)

5c

4c

3c

20

10

0

HIGH STRENGTH 150 MN/m /.I//

/

/ MEDIUM STRENGTH

LOW STRENGTH 80 MN/m3

//J - 40 MN/m?

ULTRA-LOW STRENGTH- --

20 MN/m3

TIRE PRESSURE 1.25 MPa STANDARD STRESS 2.75 MPa PCA COMPUTER PROGRAMME PDILB

S io 1 20 25 30 35 40 45 50 55

REFERENCE THICKNESS

Figure 1-4. ACN Rigid Pavement Conversion Chart


c) t h e a i r c r a f t c l a s s i f i c a t i o n number, a t the s e l ec t ed mass and subgrade k value, i s two tirnes the der ived s ingle wheel load i n 1 000 kg. Note t h a t the ACN can a l so be read d i r e c t l y from t h e char t . Note f u r t h e r t h a t t i re pressure cor rec t ions a re no t needed when t h e above procedure is used.

1.1.3.8 Flexib le pavements. This procedure uses the conversion chart shown i n Figure 1-5 and t h e pavement thickness requirement charts published by t h e a i r c r a f t manufacturers based on t h e ~ i t e d States Army Ehgineers CBR procedure. The former chart has been developed using the following expression:

Where t = reference thickness i n cm.

DSWL = a single wheel load with 1.25 HPa tire pressure

ps = 1.25 MPa

CBR = standard subgrade (Note t h a t t h e c h a r t u s e s f o u r s tandard values 3, 6, 10 and 15)

C 1 0.5695 C2 = 32.035

The r e a s o n f o r u s i n g t h e l a t t e r charts i s to obtain the equivalency between the "group of landing gear wheels effect" to a der ived s ingle wheel load by means of Boussinesq Deflection Factors. The fo l lowing s tep8 are used t o de t e rmine t he ACN of a n aircraft:

a ) u s i n g t h e pavement requirement chart published by the manufacturer d e t e r d n e t h e r e f e r e n c e t h i c k n e s s f o r t h e g i v e n a i r c r a f t mass, subgrade category, and 10 000 coverages;

b) enter Figure 1-5 with the re fe rence th ickness de te rmined in s tep a ) and t h e CBR corresponding t o the subgrade category and read the der ived s ing le wheel load; and

c ) t h e ACN a t t h e s e l e c t e d me8 and subgrade category i e two times t h e der ived s ingle wheel load i n 1 000 kg. Note t h a t t h e ACN can a l so be read d i rec t ly f rom the chart. Note f u r t h e r t h a t t ire pressure cor rec t ions are not needed when t h e above procedure Le used.

1.1.3-9 Tire pressure adjustment to ACN. Mrcraf t normal ly have the i r tires i n f l a t e d t o t h e p r e s s u r e c o r r e s p o n d i n g t o t h e m a x i u u m gross mass and maintain this pressure regardless of t h e v a r i a t i o n s i n t a k e - o f f masses. There are times, however, when operat ions a t reduced masses and reduced tire pressures are productive and reduced ACNE need t o be calculated. To d o t h i s f o r r i g i d pavements, a chart has been prepared by the u se of t he PCA computer programme PDLLB and is given i n Figure 1-6. The example included in t h e c h a r t i t s e l f e x p l a i n s how t h e c h a r t is used.

I C A O 9357 P A R T * 3 ** m 4 8 4 3 4 3 6 0019386 038 m


ACN 100 90 ul 70 60 50

40

30

20

10

REFERENCE THICKNESS CM

Figure 1-5. ACN Flexible Pavement Conversion Chart


1 . 1.3.10 For f l e x i b l e pavements, t h e CBR equation t = \ L F Z

w a s used to equate thickness and solve for the reduced pressure ACN i n terms of t h e maximm t i re pressure ACN a t the reduced mass giving the fol lowing expression:

1.1.3.11

ACN = ACN Reduced Maximm pressure pressure

(For values of C1 and C2 see 1.1.3.8.)

Worked examples

Solution: The ACN of t h e a i r c r a f t f r o m t h e t a b l e i n Appendix 5 of t h i s Manual i s 48.

It i s a l s o p o s s i b l e t o d e t e r m i n e t h e ACN of the a i r c ra f t u s ing F igu re 1-4 and the pavement requirement chart for t h e a i r c r a f t i n F i g u r e 1-7. This method involves the fol lowing operat ions:

a) from Figure 1-7 read the th ickness of concre te needed for the aircraft mass of 78 500 kg, the subgrade k value of 80 MN/m3, and the s tandard concrete stress of 2.75 MPa as 31.75 cm; and

b) enter F igure 1-4 with th i s th ickness and read the ACN of t h e a i r c r a f t f o r t h e medium strength subgrade as 2.

ICAO 9357 P A R T * 3 ** m h84L43b 0039388 900 m

P a r t 3.- Pavements 3-13

1.2

1.1

1 .o

CORRECTION FACTOR

ACN

ACNSTD

.9

.a

.7

.E

7 An aircraft with a tire pressure of 1.25 MPa has

would be its ACN if tire pressure is increased an ACN of 50 on a medium subgrade. What

to 1.50 MPa?

To obtain the correction factor proceed verti-

medium subgrade curve is intercepted. Then proceed horizontally and read 1.06.

ACN for TP 1.50 MPa = 1.06 x 50 = 53

Pavement thickness = 40 cm

- cally from a tire pressure of 1-50 MPa until

.5 .75 1 .o 1.25 1.5 1.75 2.0 2.35 2.50 TIRE PRESSURE MPa

Figure 1-6. ACN tire pressure ad jus tment - r igid pavements only

+. - _

I C A O 9L57 PART*K3 ** E 48YLYLb 0059389 847 H


Example 2: An A I P conta ins the fo l lowing in format ion related t o a runway pavement:

PCN of the pavement = 80 Pavement t y p e r i g i d

Subgrade category medium s t r e n g t h Tire p r e s s u r e l i m i t a t i o n = none

Determine whether the pavement c a n a c c e p t t h e f o l l o w i n g a i r c r a f t a t t h e indicated operat ing masses and t i re pressures:

MaSS Tire pressure - Airbus A 300 Model B2 a t 142 000 kg 1.23 MPa B747-100 a t 334 751 kg 1.55 MPa Concorde a t 185 066 kg 1.26 MPa DC- 10-40 a t 253 105 kg 1.17 HPa

Solution: ACNs o f t h e s e a i r c r a f t f r o m Appendix 5 of t h i s Manual are 44, 51, 71 and 53, respect ively. Since the pavement i n q u e s t f o n h a s a PCN of 80 i t can accept a l l of these aircraft.

Example 3: Find the ACN of DC-10-10 a t 157 400 kg on a f l e x i b l e pavement r e s t i n g on a medium strength subgrade (CBR 10). The t i re pressure of the main wheels is 1.28 MPa.

Solution: The ACN of t h e a i r c r a f t f r o m Appendix 5 of t h i s Manual is

(196 406 - 157 400) (196 406 - 108 940) 57 - x (57-27) 39 006

87 466 I 5 7 -- x 30 = 57 - 13.4 = 43.6 o r 5 It i s a l so poss lb l e t o de t e rmtne t he ACN o f t h e a i r c r a f t u s i n g F i g u r e 1-5 and the pavement r e q u i r e n e n t c h a r t i n F i g u r e 1-8. This method involves the fol lowing operat ions:

a) from Figure 1-8 read the th ickness o f pavement needed for the a i rc raf t mass of 157 400 kg and the subgrade CBR of 10 as 57 cm; and

b) en ter F igure 1-5 with this th ickness and read the ACN of a i r c r a f t or the subgrade CBR of 10 as 44.

m

e

I C A O 7357 P A R T * 3 f * H 4B414Lb 0037390 569

Part 3.- Pavements

124.5 x 43.2 cm TIRES - TIRE PRESSURE CONSTANT AT 11.7 kglcm 127 x 53.3 cm TIRES (NEW DESIGN) - TIRE PRESSURE CONSTANT AT 11.7 kg/cm*

THE MAXIMUM LOAD REFERENCE LINE AND DESIGN OF CONCRETE AIRPORT ANY VALUE OF k ARE EXACT. FOR LOADS PAVEMENT AND COMPUTER PROGRAMME

NOTE: THE VALUES OBTAINED BY USING REFERENCES:

LESS THAN MAXIMUM. THE CURVES ARE u

I C A O 9357 PART*3 ** 444lr4bb 0019391 4T5


FLEXIBLE PAVEMENT THICKNESS

cm 0 ,

25

50

75

100

125

150

175

108 862 kg OPERATING MASS EMPTY

157 396 kg MAXIMUM LANDING MASS

195 579 kg MAXIMUM TAKE-OFF MASS

I / / I I I I I I I I I I I I I t

3 5 7 9 20 40 6080 2 4 6 8 1Q 30 50 70

SUBGRADE CBR (PERCENTAGE)

Figure 1-8. DClO-10 Flexible Pavement Requirements 10 000 Coverages aft c.g.

1.2 Procedure for pavements meant f o r l i gh t aircraft:

1.2.1 The ACN-PCN method described i n 1.1 is not intended for report ing s t rength o f pavements meant f o r l i g h t aircraft, i.e., those with mass less than 5 700 kg. Annex 14 s p e c i f i e s a simple procedure for euch pavements. This procedure envisages the repor t ing of only two elements: maxirmm a l l o w a b l e a i r c r a f t mass and maximot allowable t i r e pressure. It is important t o note t h a t t h e tire p res su re ca t egor i e s of the ACN-PCN method (1.1.3.2, c ) ) are n o t u s e d f o r r e p o r t i n g maxiaum allowable t i re pressure. Ins tead , ac tua l tire pressure limits are reported as ind ica t ed in the following example:

ExafQle: 4 000 kg/0.50 MPa

CHAPTER 2. - GUIDANCE ON OVERLOAD OPERATIONS

2.1 Criteria suggested i n Annex 14, Attachment B

2.1.1 Overloading of pavements can result ei ther from loads too large or from a subs t an t i a l ly i nc reased app l i ca t ion rate o r both. Loads la rger than the def ined (des ign o r e v a l u a t i o n ) l o a d s h o r t e n t h e d e s i g n l i f e w h i l s t smaller loads extend it. With t h e exception of massive overloading, pavements i n t h e i r s t r u c t u r a l b e h a v i o u r are n o t s u b j e c t t o a par t icu lar l imi t ing load above which they suddenly o r ca tas t rophica l ly fa i l . Behaviour i s s u c h t h a t a pavement c a n s u s t a i n a de f inab le l oad fo r an expec ted number of repe t i t ions dur ing i t s d e s i g n l i f e . As a resul t , occasional minor overloading is acceptable, when expedient , wi th only l imi t ed loss i n pavement l i f e expectancy and r e l a t i v e l y small acce lera t ion of pavement de te r iora t ion . For those opera t ions in which magnitude of overload and/or the frequency of u s e d o n o t j u s t i f y a d e t a i l e d a n a l y s i s t h e fol lowing criteria are suggested:

a) f o r f l e x i b l e pavements occasional movements by aircraft wi th ACN n o t exceeding 10 per cen t above the repor ted PCN should not adversely a f f e c t t h e pavement;

b ) for r ig id o r composi te pavemepts , in which a r i g i d pavement l a y e r provides a pr imary e lement of the s t ructure , occasional movements by a i r c r a f t w i t h ACN not exceeding 5 per cen t above the repor ted PCN shou ld no t adve r se ly a f f ec t t he pavement;

c) i f t h e pavement s t r u c t u r e is unknown t h e 5 pe r cen t l imi t a t ion shou ld apply; and

d ) t h e annual. number of overload movements should not exceed approximately 5 p e r c e n t o f t h e t o t a l a n n u a l a i r c r a f t movements.

2.1.2 Such overload movements should not normally be permitted on pavements exhib i t ing s igns o f d i s t ress o r fa i lure . Fur thermore , over loading should be avoided during any per iods of thaw fol lowing f rost penetrat ion or when t h e s t r e n g t h of t h e pavement o r i t s subgrade could be weakened by water. Where overload operat ions are conducted , the appropr ia te au thor i ty should rev iew the re levant pavement condi t ion regular ly and should a l so rev iew the criteria fo r ove r load ope ra t ions pe r iod ica l ly s ince excess ive repe t i t ion o f over loads can cause severe shor ten ing of pavement l i f e o r r equ i r e ma jo r r ehab i l i t a t ion o f pavement.

2.2 S t a t e practices

2.2.1 Canadian practice

2.2.1.1 The technical assessment of a proposed overload operation is based on the "overload ratio" concept. The o v e r l o a d r a t i o i s a measure of t he l oad imposed by t h e aircraft r e l a t ive t o t he nomina l des ign s t r eng th o f t he pavement. For f l e x i b l e pavements, t he ove r load r a t io i uposed by a n a i r c r a f t is determined by c a l c u l a t i n g t h e subgrade bear ing s t rength requi red for the ex is t lng th ickness o f pavement, u s ing t he des ign equa t ion g iven i n 4.1,2.2. This ca lcu la ted subgrade bear ing s t rength i s then divided by the ac tua l subgrade bear ing s t rength to form the over load ra t io . For r i g i d

3-17

SCAO 9157 PART*3 ** W 4BL1/4Lb 00119393 278 -


pavements, the overload ratio is defined as the flexural stress imposed in the slab by the aircraft divided by the design flexural stress of 2.75 HPa.

2.2.1.2 Cn the basis of these overload ratios, aircraft operations are classified as follows:

Overload Ratio Operational Classification

less than 1.25 unrestricted 1.25 to 1.50 limited 1.50 to 2.00 marginal greater than 2.00 emergency use only

2.2.1.3 The approval of operations classified as limited or marginal involves the risk of an accelerated rate of pavement deterioration and shortened service life. This risk increases with increasing value of overload ratio and frequency of operations. The decision to approve such operations therefore depends on the willingness of the airport authority to fund pavement rehabilitation measures earlier than may otherwise be necessary. Normal practice at airports operated by Transport Canada is to permit aircraft operations falling into the limited and marginal classifications, unless otherwise dictated by age and condition of the pavement, or funding constraints.

2.2.1.4 Similar considerations apply to permitting operations by aircraft with tire pressures higher than restrictions reported. Provided the overload ratio is less than 1.50, aircraft are normally permitted to operate with tire pressures one range higher than the tire pressure range for which the pavement was designed. These ranges are indicated in 4.1.2.6.

2.2.2 French practice l 2.2.2.1 The information publiehed on the basis of one or the other method described in 4.2.8 does not permit a complete reflection of the operating condition of the pavement. The following procedure should therefore be used to assess the euita- bility of the pavement for the intended aircraft. Reference is made to the flexible pavement or rigid pavement requirement graph for the subject aircraft in Appendix 3. These graphs and the pavement data enable the exact authorized load for the particular undercarriage to be determined. In the event that the aircraft is not shown in Appendix 3, characteristics that are closest to the subject aircraft will be selected. If the resulting load is higher than the expected aircraft load , the allowable stresses of the pavement will not be exceeded, and the aircraft can use the pavement without adverse effects. Should the load established by means of the graph be less than the expected aircraft load, there will be an effective overload and acceptance of the aircraft will require special permission.

2.2.2.2 Concessions. It should be noted that the risk to the aircraft itself when landing on a runway without adequate bearing strength is minimal, unless the load it imposes is considerably more than the bearing strength of the runway. Generally speaking, the acceptance of an exceseively heavy aircraft will undoubtedly cause damage to the pavement, without detriment to the aircraft itself. The user will in no case be held responsible for deteriorations of this type. however, in no case should an aircraft load exceed by more than 50 per cent the allowable load for the subject aircraft, in other words an actual overload co-efficient P/PO higher than 1.5 for all pavements, except aprons for which these values are limited to 20 per cent and 1.2,

ICAO 7157 P A R T * 3 ** = 4 8 4 1 4 1 b 0019374 104

Part 3. - Pavements 3-19 e respectively. (For runways, t h i s r u l e does not apply t o emergency landings.) The decision to grant or withhold the concession to operate on weak runways can be arr ived a t as follaws:

a ) the to ta l equiva len t t ra f f ic suppor ted by the pavement is calculated i n accordance with the same principle expressed in the opt imized design method described i n 4.2.6; however, t h i s is reduced t o a da i ly t r a f f i c e x p r e s s e d i n terms of movements per day; and

b) i f t h e t o t a l e q u i v a l e n t t r a f f i c exceeds t e n movements da i ly , re fusa l of the concession would normally be jus t i f ied , un less more rapid wear of the runway is acceptable. Such a decis ion might be acceptable on economic grounds wi th the in ten t ion of increasing a i r t r a f f i c w i thou t having t o r e i n f o r c e pavements, at least f o r t h e time being.

2.2.2.3 On the oQher hand, i t is recommended t o l i m i t t h e number of movements invo lv ing an a i r c ra f t fo r which a concession has been granted and to undertake follow-up ac t ion wi th regard to the pavement i n accordance with the information provided i n t h e t ab le beluw:

l P/Po values I movements . respect of pavement I I M a x i u u m number of Follaw-up action i n 1.1 2 per day Follow-up

recommended 1.1 - 1.2 1 every day 1.2 - 1.3 1 per week Regular and frequent

follaw-up mandatory

1.4 - 1.5 1 per month - Remark: Enstead of cons ider ing da i ly t ra f f ic , i t would-be more s t r ingent t o consider cumdative traffic to t ake i n to accoun t t he actual magnitude of pas t t r a f f i c . This could be done where it is j u s t i f i e d for the sake of precis ion of the study.

E ~ s m p l e . A f l e x i b l e runway has the fol lowing character is t ics :

Total equivalent thickness e = 70 cm

CBR of the subgrade CBR = 8

PCN 57/P/C/W/T

It rece ives four da i ly movements of Airbus A-300 B2 with a load of 142 t (ACN = 55) and four moveaents dai ly of B-727 with a load of 78 t (ACN = 4 9 ) . Under what conditions can it be used by t h e B-747-200 with a load of 365 t ?

_.

ICAO 9157 P A R T * 3 t t 48414kb 0019395 040 W


Solut ion

Step 1. Calculation of t h e ACH of t h e B-747-200

(365 000 - 168 872) (373 306 - 168 872) ACN = 23 + (71 - 23) x = 69

The ACN exceeds the published PGN: a concession is t he re fo re r equ i r ed fo r t h e a i r c r a f t .

Step 2. Calculation of e q u i v a l e n t t r a f f i c :

Actual Allowable Actual load load movements Equivalent P Po P/Po C (mvt/d) movements

A-300 B2 142 t 142 t 1 1 4 4

B-7 2 7 78 t 84 t 0.93 0.44 4 1.8

B-747 365 t 329 t 1.11 3.52 X 3.5x

TOTAL (5.8 + 3.5 x) m t / d

For x = 1 mvt/d, t he equ iva len t t r a f f i c i s 9.3 mvt/d and lese than 10 mvt/d: t he B-747-200 may r equ i r e a concession.

For x grea ter than 1 m t / d , t h e e q u i v a l e n t t r a f f i c would exceed 10 nv t /d and the B-747-200 could not be accepted.

2.2.3 United Kingdom p r a c t i c e

2.2.3.1 Individual aerodrome authori t ies in the United mugdola are f r e e t o d e c i d e on t h e i r own criteria for permi t t ing over load opera t ions as long as pavements remain s a f e for use by a i r c r a f t . However, the following guidance i e provided:

a) a 10 per cen t d i f fe rence i n ACN over PCN involves an Increase i n pavement working stresses which are generally considered acceptable provided the following conditions are s a t i e f i e d :

1) t h e pavement i s mre than twelve months o ld ;

2) t h e pavement i e not already showing signs of l oad ing d i s t r e s s ; and

3) overload operations do not exceed 5 p e r cent of the annual departures and are spread throughout the year.

i I

P a r t 3.- Pavements 3-21

b) overload operations representing a d i f f e r e n c e i n ACN over PCN of from 10 p e r ' c e n t to 25 pe r cen t j u s t i fy r egu la r i n spec t ions of t h e pavement by a competent person in a d d i t i o n t o s a t i s f y i n g t h e a b o v e criteria. There should be an immediate curtailment of such overload operations as soon as d i s t r e s s becomes evident and the higher loading should not be reimposed u n t i l a p p r o p r i a t e pavement s t rengthening work has been completed;

C ) ovei load operat ions represent ing a d i f f e r e n c e i n ACN over PCN of from 25 p e r c e n t t o 50 per cent may be undertaken under special circum- s tances . They call f o r s c r u t i n y o f a v a i l a b l e pavement construct ion records as test d a t a by a q u a l i f i e d pavement engineer and a thorough inspec t ion by a pavement engineer before and on completion of t h e movement t o assess any signs of pavement d i s t r e s s ; and

d) over load ope ra t ions i n excess of a n ACN over PCN of 50 per cent should only be undertaken i n an emergency.

CHAPTER 3 . - EVALUATION OF PAVEMENTS

3.1 General

3.1*1 The purpose of t h i s c h a p t e r i s t o p re sen t gu idance on the evaluation of pavements t o t hose r e spons ib l e fo r eva lua t ing and r epor t ing pavement bear ing s t rength . Recognizing that responsible individuals may range from experienced pavement engineers t o a i r f i e l d managers not e n j o y i n g t h e d i r e c t s t a f f s u p p o r t of pavement behaviour experts, information will be included which attempts t o se rve t he va r ious l eve l s of need.

3.2 Elements of pavement evaluat ion

3.2.1 The behaviour of any pavement depends upon t h e n a t i v e materials of the si te, which a f te r 1eve lLing and prepara t ion i s cal led the aubgrade, i t s s t r u c t u r e including a l l layers up through the surfacing, and the BL~SS and frequency of using aircraft. Each of these th ree e lements must be considered when evaluat ing a pavement.

3.2.2 The subgrade. The subgrade is t h e l a y e r of material immediately below the pavement s t ruc ture which is prepared during construct ion to support the loads t ransmit ted by t h e pavement. It is prepared by s t r ipp ing vege ta t ion , l eve l l i ng o r br inging to p lanned grade by cut and f i l l operations, and compacting t o t h e needed density. Strength of the subgrade is a s ignif icant e lement and thiLs mst be charac te r ized for eva lua t ion or des ign of a pavement f a c i l i t y o r f o r e a c h s e c t i o n o f a f a c i l i t y e v a l u a t e d or designe'd separately. Soil st rength and therefore subgrade s t r e n g t h i e very dependent on soil moisture and m a t be eva lua ted for the condition i t i s e x p e c t e d t o a t t a i n in sieu beneath the pavement s t ruc tu re . Except i n cases wi th high water tables, unusual drainage, or extremely porous o r cracked pavement c o n d i t i o n s s o i l moisture w i l l t e n d t o s t a b i l i z e u n d e r w i d e pavements t o something above 90 p e r cent of fu l l s a tu ra t ion . Seasona l va r i a t ion ( excep t ing f ro s t pene t r a t ion o f suscep t ib l e materials) is normally small t o none and higher so i l moisture conditions are poss ib l e even i n q u i t e a r i d areas. Because materials can vary widely in t ype t he subgrade s t r e n g t h e s t a b l i s h e d f o r a p a r t i c u l a r pavement may f a l l anywhere wi th in the range ind ica t ed by the four subgrade strength c a t e g o r i e s u s e d i n the ACN-PCN method. See Chapter 1 of t h i s Manual and Annex 14, Chapter 2.

3.2.3 The pavement s t m c t u r e . The terms "rigid" and "flexible" have come i n t o u s e f o r i d e n t i f i c a t i o n o f t h e two pr incipal types of pavements. The terms attempt t o charac te r ize the response of each type to loading. The primary elereeat of a r i g i d pavement i s a l a y e r or s l a b of Portland cement concrete (PCC), p l a i n or re inforced i n any of several ways. It i s of ten under la in by a g r a n u l a r l a y e r which con t r ibu te s t o the s t ruc tu re bo th d i r ec t ly and by f a c i l i t a t i n g t h e d r a i n a g e o f water. A r i g i d pavement r e sponds " s t i f f ly" t o su r f ace l oads and d i s t r ibu te s t he l oads by bending or beam a c t i o n t o wide areas of the subgrade. The s t r e n g t h of t h e pavement depends on the th ickness and s t rength of t h e FCC and any underlying layers above the subgrade. The pavemnt rmst be adequate t o d i s t r i b u t e s u r f a c e l o a d s so that: t h e pressure on the subgrade does not exceed i ts evaluated s t rength. A f l e x i b l e pavement c o n s i s t s of a series of l a y e r s i n c r e a s i n g i n s t r e n g t h f r o m t h e s u b g r a d e t o the sur face l ayer . A a e r i e s s u c h as select: material, lower sub-base, sub-base, base and wearing couree is commonly used. However, t h e lower l a y e r s m y n o t b e p r e s e n t i n a p a r t i c u l a r pavement. The pavements meant f o r heavy aircraft usual ly have a bituminoue bound wearing course. A f l e x i b l e pavement

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y i e l d s more under surface loading merely acconglishing a widening of the loaded area and

subgrade, the layers must h a v e s t r e n g t h s u f f i c i e n t t o t o l e r a t e t h e p r e s s u r e s a t t h e i r l eve l . The pavement thus depends on i ts th ickness over the subgrade for reduct ion of t h e s u r f a c e p r e s s u r e t o a value which the subgrade can accept. A f l e x i b l e pavement must a lso have th ickness of s t r u c t u r e a b o v e e a c h l a y e r t o r e d u c e t h e p r e s s u r e t o a l e v e l acceptable by the l aye r . In addi t ion , the wear ing course must be s u f f i c i e n t i n s t r e n g t h t o a c c e p t w i t h o u t d i s t r e s s t ire p res su res o f u s ing a i r c ra f t .

@ consequent reduct ion of pressure layer by layer . A t e a c h l e v e l f r o m t h e s u r f a c e t o

3.2.4 Aircraf t loading . The a i r c r a f t mass is t r a n s m i t t e d t o t h e pavement th rough t he unde rca r r i age o f t he a i r c ra f t . The number of wheels , their spacing, tire p res su re and s i ze de t e rmine t he d i s t r ibu t ion of a i r c r a f t l o a d t o t h e pavement. In gene ra l , t he pavement must be s t rong enough to suppor t the loads appl ied by t h e individual wheels , not only a t the sur face and the subgrade bu t a l so a t intermediate levels. For the closely spaced wheels of dual and dual-tandem legs and even f o r ad jacen t l egs o f a i r c ra f t w i th complex unde rca r r i ages t he e f f ec t s of d i s t r i b u t e d l o a d s from adjacent wheels overlap a t the subgrade (and intermediate) level. In such cases, the e f f ec t ive p re s su res are those combined from two o r more wheels and nust be a t t e n u a t e d s u f f i c i e n t l y by t h e pavement s t ruc tu re . S ince t he d i s t r ibu t ion o f l oad by a pavement s t r u c t u r e i s over a much narrower area on a h igh s t rength subgrade than on a low strength subgrade, the combining effects of adjacent wheels i s much less f o r pavements on h i g h s t r e n g t h t h a n on low strength subgrades. This i s the reason why t h e r e l a t i v e e f f e c t s of two a i r c r a f t t y p e s are not . the same f o r pavements of equivalent des ign s t r eng th , and t h i s i s t h e b a s i s f o r r e p o r t i n g p a v e k n t b e a r i n g s t r e n g t h by subgrade s t rength category. Within a s u b g r a d e s t r e n g t h c a t e g o r y t h e r e l a t i v e e f f e c t s of two a i r c r a f t t y p e s on pavements can be uniquely stated with good accuracy.

3.2.5 Load repet i t ions and composi t ion of t r a f f i c . It i s n o t s u f f i c i e n t t o a consider the magnitude of loading alone. There i s a fatigue o r r e p e t i t i o n s of load V f a c t o r which should also be considered. Thus magnitude and repeti t ions must be t r e a t e d together, and a pavement which i s designed to support one magnitude of load a t a defined number of repe t i t ions can suppor t a l a rge r l oad a t f ewer r epe t i t i ons and a smaller load f o r a g r e a t e r number of repe t i t ions . It i s t h u s p o s s i b l e t o e s t a b l i s h t h e e f f e c t of one a i r c r a f t mass i n terms of equ iva len t r epe t i t i ons o f ano the r a i r c ra f t mass (and type ) . Applicat ion of this concept permits the determinat ion o f a single (selected) magni tude of l oad and r epe t i t i ons l eve l t o r ep resen t t he e f f ec t o f t he mix tu re of a i r c r a f t u s i n g a pavement.

3.2 .6 Pavement condition survey. A par t icu lar ly impor tan t ad junc t to o r p a r t of eva lua t ion i s a carefu l condi t ion survey . The pavement should be c losely examined f o r evidences of d e t e r i o r a t i o n , movement, or change of any kind. Any observable pavement change provides information on effects of t raff ic or the environment on t h e pavement. Observable e f fec ts o f t ra f f ic a long wi th an assessment of the magnitude and composition o f t h a t t r a f f i c c a n p r o v i d e a n e x c e l l e n t b a s i s f o r d e f i n i n g t h e b e a r i n g c a p a c i t y o f a pavement.

3.3 Elements of t h e ACN-PCN method

3 . 3 . 1 Pavement c l a s s i f i c a t i o n number. The pavement c l a s s i f i c a t i o n number (PCN) i s an index ra t ing (1 /500th) of t h e mass which an evaluat ion shows can be borne by t h e pavement when app l i ed by a s tandard (1.25 MPa t i r e p r e s s u r e ) s i n g l e w h e e l . The PCN r a t i n g e s t a b l i s h e d f o r a pavement i n d i c a t e s t h a t t h e pavement i s capable of support ing a i r c r a f t h a v i n g a n ACN ( a i r c r a f t c l a s s i f i c a t i o n number) of equal or lower magnitude. The ACN f o r c o q a r i s o n t o t h e PCN mst b e t h e a i r c r a f t ACN e s t a b l i s h e d f o r t h e

3-24 ~ ~ ~~~ ~~ ~ ~~ Aerodrome Design Manual

p a r t i c u l a r pavement type and subgrade category of the rated pavement as wel l . as f o r t h e p a r t i c u l a r a i r c r a f t mass and cha rac t e r i s t i c s .

3.3.2 Pavement type. For purposes of reporting pavement strength, pavements must be classixied as e i t h e r r i g i d o r f l e x i b l e . A r i g i d pavement is tha t enploying a Portland cement concrete ( K C ) s l ab whe the r p l a in , r e in fo rced , Qr prestressed and with or wi thout in te rmedia te l ayers be tween the s lab and subgrade. A f l e x i b l e pavement i s t h a t c o n s i s t i n g of a series of l a y e r s i n c r e a s i n g i n s t r e n g t h f r o m the subgrade t o t he wearing surface. Conposite pavements result ing from a PCC overlay on a f l e x i b l e pavement o r an a spha l t i c conc re t e ove r l ay on a r i g i d pavement o r t h o s e i n c o r p o r a t i n g chemica l ly ( cemen t ) s t ab i l i zed l aye r s o f pa r t i cu la r ly good i n t e g r i t y r e q u i r e care i n c l a s s i f i c a t i o n . I f t h e " r i g i d " e l e m n t r e m a i n s t h e p r e d o m i n a n t s t r u c t u r a l e l e m e n t o f t h e pavement and i s no t s eve re ly d i s t r e s sed by closely spaced cracking the pavement shou ld be c l a s s i f i ed as r ig id . O the rwise t he f l ex ib l e c l a s s i f i ca t ion shou ld app ly - Where c lass i f ica t ion remains doubt fu l , des igna t ion as f l e x i b l e pavement w i l l gene ra l ly be conservative. Unpaved su r faces (compacted e a r t h , g r a v e l , lateri te, c o r a l , etc.) should be c lass i f ied as f l ex ib l e fo r r epor t ing . S imi l a r ly , pavemen t s bu i l t w i th b r i cks , o r b locks should be c lass i f ied as f lexible . Large pre-cast s labs which require crane handl ing for p lacement can be c lass i f ied as r i g i d when used i n pavements. Pavements covered with landing mat and membrane surfaced pavements should be classified as f l e x i b l e .

3 .3 .3 Subgrade category. Since the effectiveness of aircraft undercar r iages u s i n g m l t i p l e - w h e e l s i s g r e a t e r on pavements founded on st rong subgrades cornpared t o those on weak subgrades, the problem of report ing bear ing s t rength is complicated. TO s impl i fy the repor t ing and permi t the use o f index va lues for pavernent and a i r c r a f t c l a s s i f i c a t i o n numbers (PCN and ACN) t h e ACN-PCN method uses fou r subgrade s t r eng th categories. These are termed: high, medium, low and u l t r a low with prescr ibed ranges f o r t h e c a t e g o r i e s . It f o l l o w s t h a t f o r a r epor td eva lua t ion ( E N ) t o be u s e f u l t h e subgrade category to which the subgrade of the reported pavement belongs mst be establ ished and reported. Normally subgrade s t rength w i l l have been eva lua ted in connexion with or iginal design of a pavement o r later r ehab i l i t a t ion o r s t r eng then ing . Where th i s i n fo rma t ion i s no t ava i l ab le t he subgrade s t r eng th shou ld be determined as pa r t o f pavement evaluat ion. Subgrade s t rength evaluat ion should be based on t e s t i n g wherever possible. Where evaluat ion based on t e s t i n g is n o t f e a s i b l e a r ep resen ta t ive subgrade s t rength category must be selected based on s o i l c h a r a c t e r i s t i c s , s o i l c lass i f ica t ion , loca l exper ience , o r judgement . Commonly one subgrade category may be a p p r o p r i a t e f o r a n aerodrome. However, where pavement f a c i l i t i e s are s c a t t e r e d o v e r a l a r g e area and s o i l c o n d i t i o n s d i f f e r f r o m l o c a t i o n t o l o c a t i o n s e v e r a l c a t e g o r i e s may apply and should be assessed and s o reported. The subgrade s t rength eva lua ted rmst be t h a t -i.n : Z . h beneath the pavement. The subgrade beneath an aerodrome pavement w i l l normally reach and re ta in a f a i r ly cons t an t mo i s tu re and s t r eng th desp i t e s easona l va r i a t ions . However, Ln t h e case of severely cracked surfacing, porous paving, high ground water, o r poor l oca l d ra inage , t he subgrade s t r eng th can reduce s u b s t a n t i a l l y dur ing w e t periods. Gravel and compact s o i l s u r f a c e s w i l l b e e s p e c i a l l y s u b j e c t t o moisture change. And i n areas o f s easona l f ro s t , a lower reduced subgrade s t rength can be expected during the thaw per iod where f rost suscept ible materials are involved.

3.3.4 Tire pressure category. Direct ly a t t h e s u r f a c e t h e t i r e con tac t p re s su re i s t h e most c r i t i ca l element of loading with l i t t l e r e l a t i o n t o o t h e r aspects of pavement s t rength. This is the reason-for repor t ing permiss ib le t i re p res su re i n terms of tire pressure categories . Except or rare cases of spal l - lng joints and unusual s u r f a c e d e f i c i e n c i e s , r i g i d pavements do n o t r e q u i r e t i re p r e s s u r e r e s t r i c t i o n s . However, pavements categorized as r igid which have overlays of f lexible or bi tumtnous

ICAO 9357 P A R T t 3 t t 48434Lb 0019400 238


construct ion must be t r ea t ed as f l e x i b l e pavements fo r r epor t ing pe rmis s ib l e t i re pressure. Flexible pavements which are c l a s s i f i e d i n t h e h i g h e s t t i r e pressure category must be of very good q u a l i t y a n d i n t e g r i t y , w h i l e t h o s e c l a s s i f i e d i n t h e l o w e s t category need only be capable of accept ing casua l highway t r a f f i c . While tests of bi tuminous mixes and extracted cores for qual i ty of the bi tuminous surfacing w i l l be most h e l p f u l i n s e l e c t i n g t h e t i re pressure category, no spec i f i c r e l a t ions have been developed between tes t behaviour and acceptable t i r e pressure. It w i l l usual ly be adequate, except where l imitations are obvious , to es tab l i sh ca tegory limits only when experience with high t i re pressures ind ica tes pavement d i s t r e s s .

3.3.5 Evaluation method. Wherever poss ib le repor ted pavement s t rength should be based on a " technical evaluat ion". Commonly, eva lua t ion is an inversion of a design method. Design beg ins w i th t he a i r c ra f t l oad ing t o be sus t a ined and t he subgrade s t rength resu l t ing f rom prepara t ion of t he l oca l so i l , t hen p rov ides t he necessa ry thicknesses and qual i ty of materials f o r t h e needed pavement s t ruc ture . Evalua t ion inve r t s t h i s p rocess . It begins wi th the ex is t ing subgrade s t rength , f inds th ickness and qual i ty of each component of t h e pavement s t r u c t u r e , and uses a design procedure pa t te rn to de te rmine the a i rc raf t loading which the pavement can support. Where ava i l ab le t he des ign , t e s t ing , and cons t ruc t ion r eco rd da t a fo r t he subgrade and components of t h e pavement s t ruc tu re can o f t en be u sed t o make the evaluat ion. O r , test p i t s can be opened to de te rmine the th icknesses of layers , the i r s t rengths , and subgrade s t rength for the purpose o f eva lua t ion . A t echnica l eva lua t ion a l so can be made based on measurement of the response of pavement t o l o a d . I k f l e x i o n of a pavement under s t a t i c p l a t e o r t i r e load can be u sed t o p red ic t i t s behatiour. Also t h e r e are var ious devices for apply ing dynamic l o a d s t o a pavement, observing i t s response , and us ing th i s t o p r e d i c t i t s behaviour. When f o r economic o r o the r r ea sons a t echn ica l eva lua t ion i s not feas ib le , eva lua t ion can be based on exper ience wi th "us ing a i rc raf t " . A pavement s a t i s f a c t o r i l y s u p p o r t i n g a i r c r a f t u s i n g i t c a n a c c e p t o t h e r a i r c r a f t i f t h e y are no

@ more demanding than the us ing a i rc raf t . This can be t h e b a s i s f o r a n e v a l u a t i o n . 3.3.6 Pavements f o r l i g h t a i r c r a f t . L i g h t a i r c r a f t are those having a mass of 5 700 kg or less. These a i r c ra f t have pavement requirements less t h a n t h a t of many highway trucks. Technical evaluations of those pavements can, of course, be made, but an eva lua t ion based on u s i n g a i r c r a f t i s s a t i s f a c t o r y . It is wor th no t ing tha t a t some a i rpo r t s s e rv i ce veh ic l e s such as f i r e t r u c k s , f u e l t r u c k s , o r snow ploughs may be more cr i t ical than a i r c ra f t . S ince nea r ly a l l l i g h t a i r c r a f t have single-wheel undercarriage l e g s t h e r e i s no need for repor t ing subgrade ca tegor ies . However, s i n c e some h e l i - cop te r s and mi l i t a ry t r a ine r ae rop lanes w i th in t h i s mass range have qui te high t i re pressures l imited qual i ty pavements may need t o have t i r e pressure limits es t ab l i shed .

3.4 Assessing the magnitude and composition of t r a f f i c

3 . 4 . 1 General. Pavement bear ing s t rength evaluat ions should address not merely an allowable load but a r e p e t i t i o n s u s e l e v e l f o r t h a t l o a d . A pavement which can s u s t a i n many r e p e t i t i o n s of one load can sustain a la rger load bu t for fewer r epe t i t i ons . Obse rvab le e f f ec t s o f t r a f f i c , even t hose i nvo lv ing ca re fu l measurements in Situ o r on samples i n c o n t r o l l e d l a b o r a t o r y tests, unfortunately do not (unless physical damage is apparent%) permit a determination of t he po r t ion of pavement's

* In t h e case of ev ident phys ica l damage a pavement w i l l a l r e a d y b e i n t h e l a s t s t a g e s of i ts u s e f u l l i f e .

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r e p e t i t i o n s l i f e that has been used or , conversely, i s remaining. Thus an evaluat ion leading to bearing capaci ty determinat ion i s an assessment of pavement's total expected r e p e t i t i o n s ( t r a f f i d l o a d ) l i f e . Any project ion of remaining useful l i f e of t h e pavement w i l l depend on a determination of all. t r a f f i c s u s t a i n e d s i n c e c o n s t r u c t i o n o r reconstruction.

3 . 4 . 2 Mixed loadings. Normally, it w i l l . be necessary to cons ider a mixture of loadings a t t h e i r r e s p e c t i v e r e p e t i t i o n s u s e levels. There i s a s t rong tendency to rate pavement b e a r i n g s t r e n g t h i n term of some se lec ted loading for the a l lowable repe t i - t i o n s u s e l e v e l , a n d t o rate each loading appl ied to a pavement i n term of i t s equiva- l e n t number of t h i s bas i c l oad ing . To d o t h i s , a r e l a t i o n is f i r s t e s t a b l i s h e d between loading and repe t i t ions to p roduce fa i lure . Such r e l a t i o n s are var ious ly es tab l t shed using combinations of theory or design methods and experience behaviour pat terns or l abora to ry f a t igue cu rves fo r t he p r inc ipa l s t ruc tu ra l e l emen t o f t he pavement. Obviously, not a l l r e l a t i o n s are t h e same,* but the repe t i t ions parameter is n o t s u b t l y e f f ec t ive . It needs only t o be e s t a b l i s h e d i n g e n e r a l magnitude and not Ln s p e c i f i c value. Thus f a i r l y l a r g e v a r i a t i o n s c a n ex is t in t h e l o a d i n g - r e p e t i t i o n s r e l a t i o n wi thou t s e r ious d i f f e rences i n eva lua t ion r e su l t i ng .

3 . 4 . 3 Using the cu rve fo r l oad ing ve r sus r epe t i t i ons t o f a i l u r e , t h e f a i l u r e repe t i t ions for each loading can be de te rmined and compared eo t h a t f o r t h e b a s i c selected loading. From these comparisons, the equivalent number of t h e b a s i c selected loading for s ing le appl ica t ions o f any loading are determined, i .e . , factors greater than 1 for l a rger loadings and less than 1 f o r smaller loadings. An explanatory example of t h i s p r o c e s s f ollaws:

a) relate l o a d i n g t o f a i l u r e r e p e t i t i o n s , a6 i l l u s t r a t e d in Figure 3-1;

Log load

Figure 3-1

See Chapter 4, Figure 4-29 (French practice) and 4.4.12.1 (United States practice).

ICAO 7357 P A R T * 3 ** = 4 8 4 3 4 3 6 0019402 000


b ) f o r s e l e c t e d l o a d s L, r e a d r e p e t i t i o n s r from curve

L1 - r1 L2 - '2

L3 - r3 L4 - r4

c) choose L3 as the bas ic load; and

d) compute e q u i v a l e n t r e p e t i t i o n s f a c t o r f fo r each l oad

Load - Equivalent Repetit ions Factor f l = - (a value less than 1)

'3

I 1

r3

r 2' f , = - (a value less than 1)

'3 f 3 = - = 1

r3

r3

r 4 f 4 = - (a va lue g rea te r than 1)

By use of t hese f ac to r s , t he accumula t ed e f f ec t of any combination of loads expe r i enced o r con templa t ed can be cowared t o t he bea r ing s t r eng th eva lua t ion i n terms of a se l ec t ed l oad ing a t i t s eva lua ted a l lowable repe t i t ions use l eve l ,

3.5 Techniques f o r " u s i n g a i r c r a f t " e v a l u a t i o n

3.5.1 While technica l eva lua t ion should be accomplished wherever possible, i t i s recognized tha t f inanc ia l and c i rcumstant ia l cons t ra in ts w i l l occasional ly prevent it. Since i t is most important to have completely reported bear ing s t rength information and s i n c e t h e u s i n g a i r c r a f t e v a l u a t i o n i s reasonably direct and readi ly comprehensible i t is being presented First.

3.5.2 Heavies t us ing a i rc raf t . A pavement s a t i s f a c t o r i l y s u s t a i n i n g i ts us ing t ra f f ic can be cons idered capable of s u p p o r t i n g t h e h e a v i e s t a i r c r a f t r e g u l a r l y u s i n g i t , and any ocher a i rcraf t which has no greater pavement strength requirements. Thus t o begin an eva lua t ion based on us ing a i rc raf t , the types and masses of a i r c r a f t a n d number of times each operates i n a given per iod must be examined. Emphasis here should be on t h e h e a v i e s t a i r c r a f t r e g u l a r l y u s i n g t h e pavement. Support of a p a r t i c u l a r l y heavy load , bu t on ly ra re ly , does no t necessar i ly es tab l i sh a capab i l i t y t o suppor t equ iva len t loads on a r e g u l a r r e p e t i t i v e b a s i s (see 3 . 4 ) .

I C A O 9157 PART*3 ** 4S4545b 0059403 T47


3 .5 .3 Pavement condi t ion and behaviour . There wst next be a careful examina- t i o n o f what e f f e c t t h e t r a f f i c o f u s i n g a i r c r a f t is having on t h e pavement. The condi t ion of the pavement in r e l a t i o n t o a n y c r a c k i n g , d i s t o r t i o n o r wear, and the experience with needed maintenance are of First importance. Age nust be considered s i n c e o v e r l o a d e f f e c t s o n a new pavement may nut ye t be ev ident whi le SORE accumulated i n d i c a t i o n s of d i s t r e s s may normally be evident i n a very old pavement. In g e n e r a l , however, a pavement i n good condi t ion can be cons idered t o be s a t i s f a c t o r i l y c a r r y i n g t h e u s i n g t r a f f i c , w h i l e i n d i c a t i o n s of a d v a n c i n g d i s t r e s s show t h e pavement is being overloaded. The condi t ion examinat ion should take note of r e l a t i v e pavement behaviour i n areas of in tense versus low usage such as i n and out of wheel paths or most and least used t ax iways , zones sub jec t t o maxirmm braking, e.g., taxiway turn-off , etc. Note should a l so be t aken of behaviour of any known o r o b s e r v a b l e weak o r c r l t i c a l areas s u c h as low p o i n t s of pavement g rade , o ld s t ream c ross ings , p ipe c ross ings where in i t ia l compaction was p o o r , s t r u c t u r a l l y weak s e c t i o n s , etc. These w i l l h e l p t o p r e d i c t t h e rate o f d e t e r i o r a t i o n u n d e r e x t a n t t r a f f i c a n d t h e r e b y i n d i c a t e t h e d e g r e e o f over loading or o f under loading . The cond i t ion examina t ions shou ld a l so focus on any damage r e s u l t i n g f r o m t i r e p res su res o f u s ing a i r c ra f t and t he need fo r t i r e p r e s s u r e l i m i t a t i o n s .

3.5.4 Refe rence a i r c ra f t . S tudy o f t he t ypes and masses of a i r c r a f t w i l l i n d i c a t e t h o s e w h i c h mst be of concern i n e s t a b l i s h i n g a r e f e r e n c e a i r c r a f t a n d t h e cond i t ion su rvey f i nd ings w i l l i n d i c a t e w h e t h e r t h e l o a d o f t h e r e f e r e n c e a i r c r a f t should be less t h a n t h a t b e i n g a p p l i e d or might be somewhat g rea t e r . S ince l oad d i s t r i b u t i o n t o t h e s u b g r a d e d e p e n d s somewhat on pavement type and subgrade s t rength, t h e p a r t i c u l a r r e f e r e n c e a i r c r a f t a n d i t s mass c a n n o t b e s e l e c t e

icao doc 9157 part 3

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