Road Note 29 (RN-29) •
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Road Note No. 29 was frst published in 1960 to provide a guide to the structural design o roads carrying medium and heavy trac.
!he 196" revision widened the scope to include lightly trac#ed roads$ such as those used in housing estates.
%r &. '. !hompson o the Road Research (aboratory$ %inistry
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3n 19+0$ !he !ransport and Road Research (aboratory *!RR(, in 4ritain published a design manual or new pavement construction called 5Road Note 29. 'esign is based on 74R value.
!he thic#ness o the subbase is relat related ed to the 74R 8 value o the subgrade and to the total number o standard ale loads.
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!he thic#nes thic#nesses ses o the other layers are relat related ed to the uality o the materials in the pavement itsel as well as to the trac loading by a series o curves.
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!he design charts and tables contained in Road Note 29 are derived rom the results o the !RR(:s many ull;scale road tests under 4ritish conditions o climate$ materials$ trac
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3n 19+0$ !he !ransport and Road Research (aboratory *!RR(, in 4ritain published a design manual or new pavement construction called 5Road Note 29. 'esign is based on 74R value.
!he thic#ness o the subbase is relat related ed to the 74R 8 value o the subgrade and to the total number o standard ale loads.
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!he thic#nes thic#nesses ses o the other layers are relat related ed to the uality o the materials in the pavement itsel as well as to the trac loading by a series o curves.
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!he design charts and tables contained in Road Note 29 are derived rom the results o the !RR(:s many ull;scale road tests under 4ritish conditions o climate$ materials$ trac
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Trafc Analysis •
-or the purpose o structural design$ the loads imposed by private cars do not contribute signifcantly to the structural damage caused to road pavements by trac.
!hereore$ only the number o commercial vehicles and their !hereore$ ale;loadings are considered.
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Normally$ the heavy commercial vehicles operate on the outermost lane *the slow lane,.
Trafc Analysis 7onversion actors to be used to obtain the euivalent number o standard ales rom the number o commercial vehicles. Table 1
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Thickness Design o Pavement tr!ct!re •
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Road Note 29 presented the charts or determining the minimum thic#ness o various layers o pavement structure. !he main actors used in the design are the cumulative number o standard ales$ subgrade 74R and type o materials employed.
?ter determining the trac and design period$ the subgrade$ the subbase$ the base and the surace are each considered in turn.
!"grade !he strength o the subgrade is a principal actor in determining the thic#ness o the pavement.
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!he strength o the subgrade is assessed on the 74R scale.
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Road Note 29 recommended that the water table should be prevented rom rising to within 600 mm o the fnished subgrade level.
!his may be done by sub;soil drainage or by raising the fnished subgrade level by means o an emban#ment.
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!he reuired thic#ness o subbase is determined rom the cumulative number o standard ales to be carried and the 74R o the subgrade using -ig 1.
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3n the case that 74R o the subgrade is less than 2 @ *the lowest value given in -ig 1,$ an additional 1"0 mm o subbase$ above the reuirement or 74R 2 @$ should be used. -or cumulative trac o less than 0." million standard ales$ the minimum 74R o the subbase should be 20 @. -or cumulative trac in ecess o 0." million standard ales$ the minimum 74R o the subbase should be =0 @.
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3 the 74R o the subgrade is in ecess o the minimum reuirement or the subbase$ no subbase is reuired.
Chere subbase is reuired the minimum thic#ness that should be laid are B0 mm where the cumulative trac is less than 0." million standard ales and 1"0 mm where the trac is in ecess o that value.
#ase $aterials as Recommended "y Road Note 29
#ase !he thic#nesses reuired or each o the base materials are determined by the use o -ig 2 or -ig = or -ig.> $ in terms o cumulative number o standard ales to be carried.
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!o use the charts$ it should be noticed the diDerence in )nglish and ?merican terminology.
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5Roadbase would be 54ase course 54asecourse would be 54inder course.
in
?merican
and
Fig. 2:
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!racing %o!rse •
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!he thic#ness o suracing in terms o the cumulative number o standard ales to be carried can be determined by -ig. 2$ -ig. = and -ig. > depending on the type o base material used. Road Note 29 recommended the suracing course material to be varied with the cumulative trac to be carried and the details are given in !able 2. !he suracing is intended to be laid in two courses$ ecept where the cumulative trac is less than 0." million standard ales. !he thic#nesses o suracing course are indicated in !able 2. -or cumulative trac o over 11 million standard ales the minimum thic#ness o surace course plus binder course is 100 mm. -or additional suracing thic#ness over 100 mm shown in -ig. 2$ -ig. = and -ig. >.
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Recommendation or #it!mino!s !racing in Road Note 29& (Trafc in %!m!lative tandard A'les& *)
Numerical Example A double lane highway is to be constructed for the present trac load of 2500 cvpd at the time of construction with an estimated trac growth rate of 7%. The highway is to be designed for a life time of 20 years and the !" value of subgrade is 5%. #esign the $eible pavement as per "oad &ote 2'. Adopt number of standard ales per commercial vehicle ( ).0*.
Solution: •
1, !rac on each lane E E 12"0 cvpd
2, 7umulative repetitions at the end o 20 years$ N E 12"0 =6" 1.0B E 2+2 msa
Alternative - I =, -or %#R , . and N , 2+2 msa$ a, Thickness o !"-"ase %o!rse , 2* mm with minimum !" ( +0% b) ,Thic-ness of #ense acadam "oad!ase
( / mm or
b2 , Thic-ness of "olled Asphalt "oad!ase
( 150 mm
c,Thic-ness of /urfacing 1earing ourse !ase ourse, ( 100 mm c) , inimum Thic-ness of 1earing ourse c2 , Thic-ness of !ase ourse
( 40 mm ( 60 mm
2* mm
2+2
/ mm
2+2
mm
2+2
mm
2+2
mmendation or #it!mino!s !racing in Road Note (Trafc in %!m!lative tandard A'les& *)
0n 1!r %ase n , 2+2 msa , 2+2 ' * sa msa
Alternative- II -or %#R , . and N , 2+2 msa$ a, Thickness o !"-"ase %o!rse , 2* mm with minimum !" ( +0% b, !hic#ness o (ean 7oncrete Roadbase E 21" mm c, !hic#ness o Guracing E 1>0 mm
2 mm
3 mm
Alternative - III -or %#R , . and N , 2+2 msa$ a, Thickness o !"-"ase %o!rse , 2* mm with minimum !" ( +0% b, !hic#ness o Cet %i or 'ry 4ound %acadam Roadbase E 2>0 mm c, !hic#ness o Guracing E 1"0 mm
23 mm
