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1、Engr.Imran HafeezContents Ancient Roads(5000 years ago)Modern Roads(17th&18th Centuries)Evolution Of Pavement Design Methodology Modern Trends in Design Mechanistic-Empirical Design methodsPavement performance prediction modelsSuper-pave&Perpetual pavements conceptsPavement Performance Tests/Equipme
2、nts Concept of Ancient Roads(5000 years ago)Definition:“Paths treaded by animals and human beings”Pavement Structure:Stone paved roads made of one or two rows of slabs 50 mm thick in central portion.,Roman RoadsTypes of Roman RoadsOrdinary roman roadsImportant Roman roads Built in straight line rega
3、rdless of gradient Excavated parallel trenches 40-ft apart for longitudinal drainage Foundation raised 3-ft above ground level Embankment covered with sand or mortarCROSS-SECTION(Ordinary Roman Roads)1)Foundation layer(10-24inch),composed of large stones2)Firm base 9-in thick made of broken stones,p
4、ebbles,cement and sand3)Nucleus layer about 12-in thick using concrete made from gravel and coarse sand4)Wearing surface of large stone slabs at least 6-in deep5)Total thickness varied from 3ft to 6ftOrdinary Roman roadsBottom coarse(25-40cm)made of large size broken stones in lime mortarBase coarse
5、(25-40cm)made with smaller broken stones in lime mortarWearing coarse(10-15cm)of dressed large stone blocks/slabs set in lime mortar Total thickness varied 0.75 to 1.20 mHeavily crowned central carriage way 15ft wide(total width 35ft)CROSS-SECTION(Important Roman Roads)Important Roman roads17th and
6、18th centuries.MODERN ROADS(17th&18th Centuries)TRESAGUET ROAD(1775)CROSS-SECTIONTRESAGUET ROAD(1775)The subgrade was prepared in level Layer of large foundation stone with large kerb stones at edges Base coarse about 8cm of compacted small broken stones Top wearing coarse 5cm at edges,thickness inc
7、reased towards center for providing surface drainage Sloping shoulders with side drain Total thickness about 30cm TELFORD ROAD(1803)MODERN ROADS(17th&18th Century)CROSS-SECTION TELFORD ROAD(1803)Level subgrade Large foundation stones of thickness 17-22cm Two layers of angular broken stones compacted
8、 thickness of 10-15cm Lime mortar concrete instead of kerb stones at pavement edges Top wearing coarse of 4cm thick gravel as binding layerMODERN ROADS(17th&18th Century)MACADAM ROAD(1827)CROSS-SECTION TELFORD ROAD(1803)The subgrade is compacted with cross slope Sub-base of broken stone 5cm size wer
9、e compacted to uniform thickness of 10 cm Base coarse of strong broken stone 3.75cm size compacted to 10cm uniform thickness Top layer of stone 2cm size compacted to thickness of about 5cm Total thickness approximately 25cm(20th Century)EVOLUTION OF PAVEMENT DESIGN METHODOLOGY Pavement design:1)Mix
10、design of material2)Thickness design of structural layers Pavement design philosophy:1)Empirical2)Mechanistic(Theoretical,Analytical,Structural)3)Mechanistic-Empirical Design ApproacheswRoad Note 29(TRRL,UK 1960,1970,Empirical)wRoad Note 31wThe Asphalt Institute Manual SerieswAASHTO Guide for Design
11、 of Pavement StructuresROAD NOTE 29 A guide to the structural design of Pavements for new roads TRRL,UK 1960,1970,Empirical Approach:study performance of experimental sections built into in-service road network Foundation soil CBR.Upto 7%Traffic.Upto 100 Million Eq.Standard Axles Specification of ma
12、terial given in table-4 Design life.20mm rutting or severe cracking Performance data interpreted in light of structural theory,mathematical modeling of pavement behavior,simulative testing of road materials and pavements The Structural Design of Bituminous Roads.TRRL Laboratory Report 1132 published
13、 in 1984 Structural design criteria:1)Critical stress and strain 2)Permissible strains induced by standard 40 KN wheel load at pavement temperature of 20o CROAD NOTE 29ROAD NOTE 31 A guide to the structural design of bitumen-surfaced roads in tropical and sub-tropical countries(Overseas Edition 1962
14、,1966,1977)For traffic upto 30 msa in one direction,for 30 msa use TRRL 1132 with calibration to local conditions subgrade strength by CBR method 6 Sub-grade strength classes(2,4,7,14,29,30+)8 Traffic classes(0.3.0.7,1.5,3.0,6.0,10,17,30)Design charts for 8 type of road base/surfacing materialTHE AS
15、PHALT INSTITUTE(MS-1)Thickness Design-Asphalt Pavements for Highways and streets(1964,1981,1991)Initially developed from data of AASHO Road testDesign charts in latest edition developed using DAMA elastic layered pavement analysis program that modeled two stress strain conditions (mechanistic based
16、design procedure uses empirical correlations)Roadbed soil strength characterized by Mr AC by Modulus of Elasticity and Poissons ratioThe design charts for 3 MAAT/computer program for full depth asphalt concrete or with emulsified base/untreated aggregate base are givenAASHTO GUIDE FOR THE DESIGN OF PAVEMENT STRUCTURESApproach:study performance of trial sections constructed to a wide range of overall thickness round a close loop trafficked by repetitions of known axle loadsDeveloped empirical mod
