1. Question: What are the component parts of the following
pavements? Show with the help of sketches.a) Flexible Pavementb)
Rigid pavementAnswer: a) FLEXIBLE PAVEMENTTYPICAL FLEXIBLE PAVEMENT
CROSS SECTIONDIFFERENT LAYERS OF BITUMINOUS (FLEXIBLE) PAVEMENT as
Per IRC37-202b) RIGI PAVEMNTTYPICAL RI!ID PAVEMENT SECTION!.
Question: Discss the fnction of each part! "a)Sbgradeb) Sb #asec)
#ase $orsed) Wearing $orseAnswer:A) "#BGRAE: %t is &nished '
compacted srface of earthwork on which a road pavement
rests.F#N$TI%N":1. (o bear ltimatel) the entire load of pavement
inclding the load of tra*c transmitted throgh the pavement.!. (o
provide an ade+ate ' niform spport to the road pavement.B)
"#B&BA"E: %t is a la)er of granlar material provided in between
the sbgrade ' base corse in road pavement. %t consists cheaper
material like brnt clinker ' natral gravel.F#N$TI%N":1. (o improve
the bearing capacit) of the sbgrade.!. (o improve drainage ' to
check capillar) rise of a sb soil water.'. (o eliminate frost heave
in frost a,ected area.(. (o prevent sbgrade material from working p
into the base corse.$) BA"E $%#R"E: %t is a la)er of bolders or
bricks in single or doble la)ersprovided over the sb base or
immediatel) over the sbgrade in the absence of sb base in a road
pavement.F#N$TI%N":1. (o withstand high shearing stresses imposed
pon it de to impact of tra*c on wearing corse.!. (o act as
fondation for road pavement ' to transfer the wheel loads coming
over the pavement to the sb base ' sbgrade l)ing nderneath.)
)EARING $%#R"E: %t is the top most la)er of road pavement directl)
exposed to tra*c.F#N$TI%N":1. (o distribte the tra*c load safel) to
the base corse.!. (o act as an impervios la)er so that the srface
water ma) &nd its access to base corse.'. (o prevent dst
nisance.(. (o withstand abrasion cased de to movement of tra*c.*.
(o provide a smooth riding srface'. Question: $ompare -exible '
rigid pavements ' also discss how the load distribtion takes place
in each case.Answer: ".N P%INT" %FFLEXIBLE PAVEMENT RIGI PAVEMENT%.
$%MPARI"%N1. Initia+ ,ost %nitial costis low %nitial costis high!.
Li-e s.an .ife span is small .ife span is long'. T/i,0ness
(hickness is more (hickness is less(. 1oints /oints are not re+ired
/oints are essentiall) re+ired.*. "0i++ 2 "u.er3ision0oderate skill
' less spervision is re+ired1igh degree of skill ' more spervision
is re+ired4. Re.air wor0(heir repair work is eas) (heir repair work
is di*clt.5. "ub6ra7e 2 reasonabl) good sbgrade is re+ired2 good
sbgrade is notre+ired8. Feasibi+it9 o- .ro3i7in6 un7er6roun7
wor0s%t is eas) to locate or repair ndergrond pipes below in these
pavements.%t is ver) di*clt to provide or repair ndergrond pipes
below the pavements :. %.enin6 To tra;, a-ter ,onstru,tion(he) can
be opened to tra*c shortl) after constrction(he) re+ire cing after
constrction ' ths case dela) in opening to tra*c1e,tStresses are
not indced de to temperatre variation.1eav) stresses are indced de
to temperatre variation.1!. Resi+ien,9 (he) are more resilientto
tra*c load(he) are less resilient to tra*c load1'. Be/a3iour wit/
sub6ra7e sett+e=ent(he) ad3st according to an) deformation of
sbgrade withot rptre(he) don4t ad3st according to an) deformation
of sbgrade withot rptre1(. Tra;, suitabi+it9(he) are sitable for
allt)pe of tra*c(he) become nois) nder iron wheel tra*c1*.
$orru6ations (he) develop corrgations(he) do not develop
corrgations14. Tra,ti3e resistan,e(he) o,er more tractive
resistance(he) o,er less tractiveresistance15. Ni6/t
3isibi+it9#lack top provides poornight visibilit) %t provides good
night visibilit)18. E>e,t o- +oa7in6(he) ad3st themselves to
normal loading b) ndergrond elastic deformation(he) tend to act as
beam or cantilever ' resist deformation1:. Maintenan,e ,ost
0aintenance cost is high0aintenance cost is low
L%A I"TRIB#TI%N IN FLEXIBLE PAVEMENT(he -exible pavement la)ers
transmits the vertical or compressive stresses to the lower la)ers
b) grain to grain transfer throgh the points of contact in the
granlar strctre. 2 well compacted granlar strctre consisting of
strong graded aggregate can transfer the compressive stresses
throgh wider area and ths forms a good -exible pavement la)er. (he
vertical compressive stresses are maximm on the pavement srface
directl) nder the wheel load ' is e+al to the contact pressre nder
the wheel load. De to the abilit) to distribte the stresses to a
large area in the shape of trncated cone5 the stresses get
decreased at lower la)ers. Loa7 istribution In Ri6i7 Pa3e=entRigid
pavement possess noteworth) -exral strength. (he stresses are not
transferred from grain to grain to the lower la)ers as in case of
-exible pavements. (he rigid pavement has the slab action and is
capable of transmitting the wheel load stresses throgh wider area
below.(he rigid pavement doesn4t get deformed to the shape of the
lower srfaces as it can bridge the minor variations of lower
la)er.(. Question: Describe $.#.R test on soil sbgrade. Discss its
limitations. Answer: $.B.R. Test ? $a+i-ornia Bearin6 Ratio Test:
(he strength of the sbgrade is an important factor in the
determination of the thickness re+ired fora -exible pavement. %t is
expressed in terms of its 6$alifornia #earing Ratio45 sall)
abbreviated as 6$.#.R.4. (he reslts obtained b) these tests are sed
in con3nction with empirical crves5 based on experience5 for the
design of -exiblepavements. (he test is arbitrar) and the reslts
give an empirical nmber5 expressed sall) in per cent5 which ma) not
be directl) related to fndamental properties governing the shear
strength of soils5 sch as cohesion and angle of internal friction.
1owever5 attempts have been made recentl) to correlate $#R vale
with the bearing capacit) and plasticit) index of the soil.T/e
$a+i-ornia bearin6 ratio @$BR) is de&ned as the rate of the
force per nit area re+ired to penetrate a soil mass with a standard
circlar plnger of 78 mm diameter at the rate of 9.:7 mm;min to that
re+ired for the corresponding penetration of a standard material.
(he standard material is crshed stone and the load which has been
obtained from a test on it is the standard load5 this material
being considered to have a $#R of 988,orts shall be pt in to
simlate in the laborator) the pressre and the moistre conditions to
which the sbgrade isexpected to be sb3ected in the
&eld.Pre.aration o- test s.e,i=en: (he test ma) be performed on
ndistrbed specimens or on remolded specimens which ma) be compacted
either staticall)or d)namicall).#n7isturbe7 s.e,i=ens shall be
obtained b) &tting to the mold5 the steel ctting edge of 978 mm
internal diameter and pshing the mold as gentl) as possible into
the grond. When the mold is s*cientl) fll of soil5 it shall be
removed b) nder digging. (he top and bottom ndersrfaces are then
trimmed to give the desired length to the specimen.%f the specimen
is loose in the mold5 the annlar cavit) shall be &lled with
para*n wax ths ensring that the soil receives proper spport from
the sides ofthe mold dring the penetration test. (he densit) of the
soil and the water content of the soil mst be determined b) one of
the available standard methods.Re=ou+7e7 s.e,i=ens mst be prepared
in sch a wa) that the dr) densit) and water content correspond to
those vales at which the $#R vale is desired. (he material shall
pass a :8"mm %S sieve. 2llowance for larger material shall be made
b) replacing it b) an e+al amont of material which passes a :8 mm
%S sieve bt is retained on ?.@7 mm %S Sieve."tati,a++9 ,o=.a,te7
s.e,i=ens ma) be obtained b) placing the calclated mass of soil in
the mold and pressing in the displacer disc5 a <er paper
being placed between the disc and the soil. (he pressing ma) be
stopped when the topof the displacer disc is -sh with the rim of
the mold.9na=i,a++9 ,o=.a,te7 s.e,i=ens ma) be obtained b) sing the
standard metal rammer in accordance with A%S! :@:8 BPart
C%%)D9EFGDDetermination of water contentDdr) densit) relation sing
light compactionH or A%S! :@:8 BPart C%%%)"9EFGDDetermination of
water contentD dr) densit) relation sing heav) compactionH. (he
mold with the extension collar attached shall be clamped to the
base plate. (he spacer disc shall be inserted over the base plate
and a disc of coarse <er paper placed on the top of the
spacer disc. 2fter compacting the soil into the mold5 the extension
collar shall be removed and the top of the sample strck o, level
with the rim of the mold b) means of a straight edge. (he
perforated base plate and spacer disc shall be removed for
recording the mass of the mold and the compacted soil. 2 disc of
coarse <er paper shall be placed on the perforated base
plate5 the mold and the compacted soil shall be inverted5 and the
perforated base plate clamped to the mold with the compacted soil
in contact with the <er paper.%n both cases of compaction5 if
soaking of the sample is re+ired5 representative samples of the
material shall be taken both before compaction and after compaction
for determination of water content. %f the sample is not to be
soaked5representative sample of the material after the penetration
shall be taken for thedetermination of the water content.Test
.ro,e7ure: (he mold containing the specimen5 with the base plate in
position5 shall be placed on the lower plate of the loading
machine. Srcharge weights5 s*cient to prodce a pressre e+al to the
weight of the base materialand the pavement5 shall be placed on the
specimen. %f the specimen has been soaked previosl)5 the srcharge
shall be e+al to that sed dring the soaking period. (he annlar
weight above which the slotted weights are placed prevents the
pheaval of the soil into the slots of the weights. (he plnger shall
be seated nder a load of GE.: I B? kg) so that5 fll contact is
established between srface of the specimen and plnger. (he dial
gages of the proving ring and those for penetration are set to
Jero. (he seating load for the plnger is ignored for the prpose of
showing the load penetration relation. .oad shall be applied sch
thatthe rate of penetration is approximatel) 9.:7 mm;min. .oad
readings shall be recorded at penetrations of 85 8.75 9.85 9.75
:.85 :.75 ?.85 7.85 @.75 98.8 and 9:.7 mm. (he maximm load and
penetration shall be recorded if it occrs for a penetration of less
than 9:.7 mm. (he plnger shall be raised and detached fromthe
loading machine. 2bot 8.7 I B78 g) of soil shall be collected from
the top G8 mm la)er of the specimen and the water content
determined as per %S! :@:8 BPart"%%)"9E@G. (he presence of an)
oversiJe particles shall be veri&ed which ma) a,ect the reslts
if the) happen to be located directl) below the penetration
plnger.(he penetration test ma) be repeated for the reverse end of
the sample as a check. CALIFORNIA BEARIN! RATIO TEST
SETUPLoa7&.enetration ,ur3e.oad vs penetration crve is plotted.
(his crve will be mainl) convex pwards althogh the initial portion
of the crve ma) be concave pwards de to srface irreglarities. 2
correction shall then be applied b) drawing a tangent to the pper
crve at the point of contra -exre. (he corrected crve shall be
taken to be this tangent pls the convex portion of the original
crve with the origin of penetrations shifted to the point where the
tangent cts the horiJontal penetration axis as illstrated belowL%A
3s PENETRATI%N $#RVE" F%R $BR TE"T$BR 3a+ue: $orresponding to the
penetration vale at which the $#R is desired5 corrected load shall
be taken from the load penetration crve and the $#R calclated as
follows!CBR=PTPS 100PT K $orrected nit Bor total) test load
corresponding to the chosen penetration from the load"penetration
crve5 andP" K standard nit Bor total) load for the same depth of
penetration as for P( taken (he $#R vales are sall) calclated for
penetrations of :.7 mm and 7 mm. Lenerall)5 the $#R vale at :.7 mm
penetration will be greater than that at 7 mm penetration and in
sch a case the former shall be taken as the $#R vale for design
prposes. %f the $#R vale corresponding to a penetration of 7 mm
exceeds that for :.7 mm the test shall be repeated. %f identical
reslts follow5 the $#R corresponding to 7 mm penetration shall be
taken for design.(he $#R vale shall be reported correct to the
&rst decimal place."TANAR L%A TABLE F%R $.B.R. TE"T#se o- $BR:
Design crves have been developed b) di,erent athorities for
determining the appropriate thickness of constrction above sbgrade
materials of known $#R for di,erent wheel loads and tra*c
conditions. (his approach is one of the poplar ones for the design
of -exible pavements. ()pical design charts developed b) the Road
Research .aborator)5 .ondon5 which are also sed in %ndia5DESI!N
C"ARTS FOR FLEXIBLE PAVEMENTS - CBR MET"OD$#RVEN#MBER %F VEAI$LE"
BAC @D't)2 8"97# 97"?7$ ?7"978D 978"?78> ?78"9788F 9788"?788L
=ver ?788USE OF CBR IN DESI!N OF FLEXBLE PAVEMENT.%0%(2(%=IS! (he
main .imitation of the $#R test is that it does not correctl)
simlate the shearing forces imposed on sb"base and sbgrade
materials as the) spport highwa) pavements. For example5 it is
possible to obtain a relativel) high $#R vale for a soil containing
rogh or anglar coarse material and some amont of troblesome cla) if
the coarse material resists penetration of the piston b) keeping
together in the mold. When sch a material is sed in highwa)
constrction5 however5 the performance of the soil ma) be poor5 de
to the lbrication of the soil mass b) the cla)5 which redces the
shearing strength of the soil mass.
