Upload
bkollarou9632
View
232
Download
0
Embed Size (px)
Citation preview
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 1/8
xtending
Flexible
Pavement
Life Using Geogrids
By
Jim
Penman
CGeol
FGS
and
Joe Cavanaugh
P E
PROFESSION L
DEVELOPMENT
SERIES
Se
pt
mb
r
2006
U T
H
T
n l
l T O
W
• • • • . e INTERNATIONAL
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 2/8
Professional Development Series
G
ogrids have been
in
common use for more than 25 years.
Whi
le they
have gained widespread acceptance as a so
luti
on to problems associated
with roads constructed on soft or problematic subgrades, their
use
on
competent subgrades has been less common.
Clear
well-established design methodology is
now available that allows the design engineer to quantify the benefits of using geogrids to
extend pavement design lif
e.
This approach can be applied for the design
of
major highways
or light-duty pavements associated with local housing or retail store developments.
Instructions
The Professiona
l
Development
Series s
a
unique
opportunity
to earn continuing
education
credit. If
you
read the following
sponsored
article
and
di
splay your undmtanding of
the stated
learning objectives, you can
fulfil l a portion
of
your continuing
education requ
i
rements
at no
cost
to you.
This
article also
is
available online at WINW.zweigwhite.com/media/pdh/index.asp.
First, review the leam ing objec tiws below, then read the
Professional Development Series article. Next, complete the quiz
on
page
8 and
submit your answers to the
Professional
Developmen
t
Series sponsor.
Submittal instructions are provided
on the
Reporting
Form
on
page
PDH
7,
wnich is
also
available
for download at WINW.zweigwhite.com/media/pdh/index.asp.
Your quiz
answers
w
il
l
be
graded by the Professional
Developmen t Series
sponsor
.
If you answer
at
least 80
percent of
the
ques
t
ions
correctly,
you will
receive
a certificate of comple
tion from the
Professional
Development
Series sfX>nsor
within
90
days
and wi ll be awarded
1.0 professional
development hour
equiva lent to 0.1 continuing education unit
in
most
states).
Note: It s
the
responsibility
of
the
licensee to determine
if
this
method of continuing
education
meets is
or
hergoveming board s)
of registration s requirements.
Learning Objectives
1) Understand the mechanisms by
which
geogrids rein
force pavement structures and
how
the benefits
of
using geogrids can
be
quantified.
2) Develop a general understanding of the design
methodology
currently prescribed
by
AASHTO for
including the benefits
of
geogrid reinforcement in flex
ible pavement structures.
3) Gain insight on
how
these techniques can provide cost
effective solutions, even on relatively low-volume pave
ments.
4) Develop a ba
sic
understanding
of
state-of-the -
art
mechanistic-empirical design techniques and how
these methods will enhance pavement design practices
in the future.
Professional Development Series Sponsors
CONTECH Earth Stabili
zation
So
lutions
Inc.
Tensar
International
Corporation
Geogrid technology has developed steadily since the
products were first introduced in the early 19805. The initial
geogrids rapidly gained popularity
within
the civil engineer
ing industry, principall y due to their ability to provide simple,
cost-effective solutions in various roadway and grade separa
tion applications.
A
geogrid is a regular grid structure
of
polymeric material
used
to
reinfOfCe
soil
or
other geotechnical engineering related
materials. Products generally are classified
as
either uniaxial
geogrids
or
biaxial geogrids, depending upon whether their
Figure 1: Uniaxial UX) and
biaxial BX) geogrid
strength
is
predominantly in one
or
two directions. Uniaxial
geogrids are principally used in
grade separation applications
such as retaining walls and steep
slopes; biaxial geogrids are used
mainly in roadway applications.
Examples of
both
geogrid types
are shown in Figure
1.
This article is principally
concerned
with
the use
of
biaxial
geogrids in base reinfOfCement
applications. In these situations, the existing subgrade is
of
a
firm
nature or has been rendered such through the use
of
a
subgrade
improvement
te<:hnique. One of the principal failure
Figure
2:
The inclusion of
8X
Geogrids provides lateral confine
ment of the
base,
which
results
in enhanced pavement
pe
rform
ance - either
an
increase in the pavement life, a decrease in the
required thickness of the pavement, or a combination of the two.
_ ~
.
.. <OnI\tI«I
~
tM
IJI.Goo.,uM<l
......
- -
POH Spedal Advertising Section - CONHCH Earth Stablization Solution$ In(./Ten$af International Corp.
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 3/8
Extending
Flexible
Pavement
Life
Table
l:Keygeogrid propertiesdescribed
by1he
us.
ArrrryCorpsciEngineEfS
Geogrld Prop rty
Rib
Shape
properties Thickness
Aperture
properties
Junction strength
Overall
Stiffness
Size
Shape
Stiffness
Torsional
strength
Stability
Judgment
Rectangular
Is
better
Thicker Is better
High stiffness
Is
better
Should
be
matched totill type used
Round or square
Is
better
High stiffness
Is
better
High compared to rib strength (>90%)
High
Is
better, minimum of
0.65 cm-kgr
recommended
High
Is
better
mechanisms of a pavement under
these
firm
subsoil
conditions
is
rutting resulting from progressive lateral movement of the
aggregate base course during traffic loading (Figure 2).
The amount of lateral movement can be reduced greatly
by including a biaxial geogrid within, or at the bottom of, the
base
course
layer,
Partial penetration of coarse aggregate
particles through the geogrid apertures and subsequent
compaction results
in
mechanic
al
interlock or confine
ment of the aggregate particles.
Table 2:Typicallayer coefficients for
pa
vement materials
Material
As
phalt surface cour
se
Aspha
lt
base
cour
se
Dense-graded aggregate
Granular sub-base
Geogrid technology
Typical layer
coefficie
nt
,
0 1
0.40 - 0.44
0.30
-
OAO
0.10 - 0.14
0.06 - 0.1 0
The principal benefit of using a geogrid within the
unbound aggregate component of a flexible pavement is
ess
rutting at the surface because of reduced late
ral
spreading of
the unbound aggregate. However,
an
additional feature of the
reinforcement is that the geogrid-confined aggregate r
esults
in a much stiffer
base
course layer and a lower dynamic deflec
tioo of the pavement structure during traffic loading.
Fat
igue
cracking of the asphalt
is
therefore reduced
because
of the
presence of the geogrid reinforcement.
In
ord er for geogrids
to wor
k successfully
in base
reinforce
ment applications, they must
have
the capacity
to
facilitate
efficient load transfer between the aggregate and the
geogrid. Webster (1992) reported on a large-scale
resea
r
ch
program undertaken by the
U.S.
Army Corps of Engineers
(Corps) to investigate and determine the key physical proper
ties
of a geogrid requir
ed to
create optimal interaction and
load transfer. A summary of the
key
material properties deter
mined in the study are presented
in
Table 1.
Ta
bl
e
3:
Typica l
drainag
e coe
ffi
c
ient
s for
unbound pavem
en t materials
Qu.lI.,. of
cl<ai
n.. .
E>c<.Uent
'
r
-
'1 poor
Pfopootlotl
oft "",
p_ ment I. opproachlng .
u, .
...
< I I _S S_2S
1.40-1.15
1.1
5 -
1.10 1
l(l-1.2O 1.20
1.35 - 1.25 L25 - 1.15 1.15 -
1.
00
'00
1.15-1.15 1.15
- I.oS
1.
00-0.00
.00
I.IS-1.05 1.0
5 -
O.ao
0.00-0.60
.00
1.
05 _ 0.95 0.95 _0,75 0,75 _ 0.40
000
Current design practice for
flexible pavements
The American Association of State
Highway and Tra nsportation Officials
(AASHTO) provides guidelines for the design of
flexible pavements in its current design guide
AASHTO,
1993), The design methods described in the guide are
based
on a purely empirical approach following a set of large-scale
tests
undertaken
in
Ottawa, 111.
in
the late 1950s.
The designer is required to know the following input
parameters for a proposed pavement section:
Structural
Number SN)
- This is determined by
adding the structural cOfltributioflS from
each
of the pave
ment
layers, as
shown
in
Figure
3.
Structural Number
SH _ I
IOAl
_ OA2
ACC B I
a
0.01(1
SH _ Z.OAO_O.80
'1
liliIIIIiIII
'
, - ~ : : ~ ~ ~ a_ O
I4.m
_ l.O
~ C ' N C C O C • , C . ~ o ~• o 7 . ~ o . . . ~ : - . . .
SH_ . 0.
. 1 . 0
_ O
&S
• - IIY'I' coet'llclent (lypIc:al .a l
. . . . .
hown In r oblel)
m _ dralnage f .o, Ityplcal
.a
l
. . . . .hown In
Ta b 3)
Figure 3:
Ca
lculati
on
of
the
St
ructural Number for a
pavement
section.
Standard Nonnal Deviate
ZR
- This
parameter det
er-
mines the probab il ity that a road will maintain
an
acceptable
level of serv iceab ility during i
ts
design life. Typical values of reli-
ability recommended by MSHTO
are
presented
in Table 4, and
the relationship between reliability and the required input
parameter, ZIl is shown in
Table 5.
Standard Deviation -
Th is parameter d
escr
i
bes
the
reliability of the input parameters selected for the local condi
tions. Default values of 0.40
to
0.50 are recommended for
flexible pavements.
Change n Serviceability apSI)
-
Th is describes the
loss
in serviceability during the design life of the road and is
dictated by acceptable levels of c
ra
cking, rutting, etc.
An
initial serviceability, P of 4.2 is normally assumed, and
AASHTO recommends a terminal serviceability,
P
r
of
2.S or
higher for a major highway and 2.0 fo r highways with
less
traffic. Once P and P
r
are determined, apsi
'
P
-
Pro
Subgrade Resilient Modulus M
R
) -
Th
is
defines the
strength of the subgrade
or
foundat ion
1ayer
on which the
Tabl
e4:
Recommended
reliability
for
roads based on AASHTO (1
993
)
F u n c t i o n ~ c I ~ s s i f i c a t i o n
Interstate and other
f.eeways
Principal Arte.ials
Collectors
Local
Recommended
level of reliability
(' til
Urban
Rural
85-99.9 80-99.9
SO-99
75
-95
SO-95
75
-95
50 - 80 50 -
SO
Special Adverti$ing Section - CONTECH Earth Stablization Solution$ln(./Ten$ar International Corp.
PD"3
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 4/8
main pavement sits.
Once these input parameters
have been
determined, it is possible to calculate the
allowable traffic capacity, W
1
for a particular
pavement section using the following equation:
Jog ,, (w,. ) _ Z. S, +9.36Jog,, (SN + J) - 0.20 +
I
PSI
I
og 4 2 U
. ' 1094 +2.321og M.-8.07
0.40+ SN+ l
/
The allowable traffic capacity determined using this equa
tion
is
quoted in Equivalent Standard Axle
Loads (ESALs). To
put
this into perspective, a typical, fully laden 20-ton truck
would impose a load equivalent to approximately 5
ESALs.
Geogrids
in
flexible pavement designs
Geogrids were invented in the late 19705 and sold
commercially for the first time in the early 1980s. Clearly, they
were
not used
in the original road test
used
to develop the
current
AASHTO
design methodology for flexible pavement
design. However, guidance for incorporating geogrids for
base
reinforcement
in
flexible pavements is given in the
Interim Standard
PP46-01
published by
AASHTO in
2001.
This document recognizes that geogrids used
in
flexible
pavements provide one or both of the following benefits:
• extension of pavement design life; and
• reduction of pavement layer thickness.
t is
further stated
in AASHTO s
PP46-01
that
to
quantify
these performance benefits for a particular geogrid, it is
n e e s ~ r y
to undertake large-scale performance testing under
carefully controlled (OnditiOflS. A good summary of the test
ing undertaken during the first 20 years since geogrids were
introduced s provided by
Perkins
and Ismeik (1999).
Irrespective of the type of test undertaken, the objective
s
the ~ m - quantify the improved performance
of
geogrid
reinforced pavement sections compared with unreinforced
test sections.
133 kN 133 kN
Un re inforced Reinforced
Figure 4: Performance benefits for extended design life
Table 5: Relationship bet
wee
n Reliability and
Standard Normal Deviate,4,
Reliability Z, Reliability Z,
99 99
-3.750
92
-1
.405
99 9
-
3.090
91 -1
.340
99
-2.3
27
90
-1
.282
98
-2 .054
85
-
1.03
7
97
-
1.
881
80
-0.84
1
96
-
1.7
51
75
-0
.674
95
-1.645
70 -0
.524
9
-1.55S
60
-0.253
93
-1
.476
50 0
Quantifying extended design life for geogrid-
reinforced pavements
Consider the two pavement sections shown in Figure
4.
The sections
are
identical apart from the fact that the rein
forced pavement contains a geogrid at the subgrade-base
course interface.
The parameter generally used to quantify the extension
of
pavement design life using geogrids
is
the Traffic Benefit Ratio
TBR). This
is
defined
as
follows:
T R = No. of
cycles
for
given
deformation in
reinforced
section
No.
of
cycles for giveo defOfmation
in unreinfOfCed
sectioo
The results shown in Figure 4 are from the Corps testing
undertaken by Webster (1992). In this simple example, the
TBR would
be
calculated
as
follows:
TBR
= 500/106 =
4.72
In other words, the
use
of a geogrid in this pavement
section extended the pavement design life (for a 1 inch
surface rut) by a factor
of
4.72.
The
AASHTO
design guide methodology described above
can
be used to
calculate the allowable traffic for
an
unrein
forced pavement. To determine the extended pavement life
when using a geogrid
in
the
same
pavement
sectiOfl,
this value
is
simply multiplied by the appropriate
T R
value for the
Pow onttypo
PDH Spedal Advertising Section CONHCH Earth Stablizatlon Solutlon
In(./Ten ar
International Corp.
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 5/8
Extending Flexible Pavement
Life
M In. .ocr -.. . . . . eo.....
; J:O ... Asphlltl l '
6.0
In
. -'P
....
' ..
C·
~ n k > l < e d . , . , a
d
U
i
ng <, ,,, oction
"l.NYt", orr l
'
1.5
I.
of ..,"-il
. f td , _I t s h
80%
reduct loll
III
, ... ' . . . - 11 <IIP'<lty
ofu..,
Pl'Y""'ent.
Figure
5: Premature p.1vement failure.
geogrid concerned.
Keep
in mind, however, that in accordance
with the directions given
in
PP46-01, any T R values used for a
particular geogrid must
have been
determined using testing
methods correlated to observed field perfOfTllance .
Geogrid use in local subdivision developments
The previous sections described the general methods by
which geogrids
can be used
to extend pavement design life.
This section focuses on how this technology can be applied
to
solve
a specific problem associated with relatively light
duty pavements.
As
the population of our towns and cities continues to
expand rapidly, new or recently constructed housing, in the
form of subdivision developments, is becoming increasingly
commonplace. One of the more frequent problems
associ
ated with the roads
in
these developments
is
a direct result of
their method of construction.
Phased
construction (Figure 6) has become an extremely
common practice, particularly
so in
residential developments.
To build a roadway to gain site
access,
contractors initially
place the aggregate component of the pavement and, usually,
a thin asphalt layer on top. This technique
is
surface layers
at considerable expense.
If ruts
have
developed, it will
also
be necessary
to
replace the granular foundatiOfl
layer s).
Consider the three pavement sec tions
shown
in
Figure
5.
The trafficking capacity
in each
case
has been calculated using the AASHTO guidelines
described above.
Strange
as
it may sound,
in
this typical example, leaving off
the 1.S inches of asphalt surfacing during a phased-construc
tioo procedure (Section B) reduces trafficking capacity
of
the
pavement by more than 80 percent.
For
subdivisioo
roads,
however, the majority of the total trafficking
is
experienced
during construction
of
the road itself and the surrounding
housing. Therefore,
it
is
not
surprising that when the surface
layer is installed at the end of construction, the rest
of
the
pavement structure is approaching the end
of
its design life.
Placement of
an
additional thin surface layer results in some
additional trafficking capacity, but a year or
two
later the road
starts to show the
sort of
surface
distress
indicative of problems
associated with the structural integrity of the lower layers.
The simple solution to this problem s a layer of geogrid
installed at the bottom or within the
base
course during initial
construction. The allowable trafficking determined for
SectiOfl
C in Figure 5
was
calculated by applying a T R value of 6 (typi
cal
for a high quality geogrid with the required supporting
performance data) to the trafficking capacity for Section
B.
The
outcome is that the trafficking capacity of the thinner road used
during the construction
phase exceeds
that for which the
completed road (Section A)
was
originally designed.
From the road owner's perspective, for relatively little addi
tional expense at the start of construction, the lifetime
of
their
road is extended enormously, and expensive and disruptive
rehabilitation or reconstruction activities are avoided.
Geogrid use in retail store developments
Another
use of
geogrid technology
can be
found in the
particularly useful when local trenches
are
required for installation
of
utility pipes and
cables.
Once the overall
site
development
is
completed, the remaining asphalt is plaCed,
ensuring that the road is in pristine condition
on Day 1 of its formal
use.
Or
is
it?
Figure
6: A typical subdivision
road
during construction
surface aspha
lt
layer has
not yet
been
installed.
on
which
the
th in
Pavement distress
in
the form of asphalt
cracking at the surface
is
common on roads
within subdivisions (Figure
7). In
many
cases,
these cracks start to appear shortly after
constructiOfl - perhaps
as
soon
as
one or
two
years.
Once the cracking
starts to
develop, the
deterioration accelerates very quickly. Pavement
distress
depicted by alligator cracking s the
most common in
such
developments and
points to
an
overall integrity problem
as
the
pavement approaches the end of its design life.
Under these circumstances, the current owner
of the road will need to replace the road's
Special Advertising Sec:tlon -
CONTECH
Earth Stabllzation Solutions In(./Tensar Interna tional Corp.
PD S
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 6/8
development
of
pavements around retail
stores. Typically, thicker, heavy-duty pave
ments
are
adopted
in
the loading
areas
around such stores, while thinner, lighter-duty
pavements
are
used
for the
car
parking
areas,
One of the main problems associated with this approach s
the potential for a bath tub effect - the subgrade is at a
lower
level
in the
areas
of the heavy-duty pavements,
These
areas are
prone
to
water ingress and build up, resulting
in
a
reduction in the long-term strength of the pavement.
In
colder regions, these
areas
are
also
more susceptible
to
the
effects of freeze-thaw activity. Both of these situations reduce
the design life of the pavement, but there are additional prac
tical problems for the contractor associated with this more
complicated method
of
construction.
Consider the
two
sets of pavement sections shown in
Figure
8, In each case,
the trafficking capacity
of
the geogrid
reinforced sections s at least
as
great
as
the unreinforced pave
ment sections.
Clearly,
the reinforced sections offer cost
benefits because they
are
thinner and require less material.
However, the major advantage of this scenario is gained from
the fact that the light- and heavy-duty sections
are
of the
same
thickness, which creates a uniform subgrade elevation, In
addition to offering protection against the bathtub problems
described above, the reinforced se<:tions offer significant mate
rial cost savings. Additional benefits result from increased
speed of construction - fewer stake-out procedures,
less
undercut/disposal of fill, and simpler construction.
A glimpse
into the future
As
previously stated, the current design approach prescribed
by
AASHTO
is
based
purely on empirical
results
from the large
scale
field tests undertaken in Ottawa,
III.,
in the late 19505.
New pavement design approaches,
based
on
me<:hanistic
empirical (M-E) principles,
are
now being developed and
refined by
AASHTO
and other entities.
DesIgn
Scenario - Proposed
a ~ e n t
Section
Stlnda
rd
Duty
Heavy
Duty
Standa r
Duty
lU,OOO Es-.I:s
121.000 ESAI. .
Deslan Scenlrlo 8 . K I 1 I a i l y ReInforced P a ~ , e n t Sect10n
Standa r Duty
Heavy
Duty Stlndard
Du
ty
8lu1 Geoptd
- - -
65 000 ESAI. . 330,000
Es-. .'s
165,000
ESAI. .
F
gure 8: Biaxial
geogrids
create
uniform
subgrade elevations.
Essentially,
M-E pavement design involves the
use of
numerical modeling
te<:hniques
to
predict accurately the
stresses and strains developed in a particular pavement
section
as
a result of traffic loading. The mechanistic (or theo
retically-based) predicted performance
s
then calibrated with
field tests (empirical data) to validate the methodology.
Figure 7: Condition of a sutxlivision
road
only two to three years after
fina
l paving.
Official publication of the new
AASHTO
design guide may
still
be several years away, but
the availability
of
M-E-based design methods incorporating the
use
of geogrids within the pavement structure
is
imminent.
Researchers
at the University
of
Illinois at Urbana-Champaign are about to
publish the results of a four-year project investi
gating the
use
of geogrids in
base
reinforce
ment applications. Although this type of work
has been undertaken previously by several
authors, the
scale
of the testing undertaken at
the University of Illinois
to
develop accurate
transfer functions s unprecedented. Similarly,
the discrete element modeling approach
used
to define the interaction between the geogrid
and surrounding
soil is
revolutionary.
PDH
This eagerly anticipated advancement
in
pavement design will be published by the
University of Illinois at the 86th Annual Meeting
of the Transportation Research Board (TRB)
in
Washington, D.C., Jan. 22-26, 2007.
Spedal Advertising Section - CONHCH Earth Stablizatlon Solutlon$ In( ,/Tensar International Corp.
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 7/8
Summary
Extending
Flexible
Pavement
Life
Evalu
ation of Geosynthetic Reinforced Base
Course Layers
in
Flexible Pavements: Part I
Experimental Work, Geosynthetics Inter
national, Vol. 4 No.6, pages 549-604.
•
Webster
S.L. 1992, Geogrid Reinforced Base
Geogrids can be used successfully to extend the design life
of flexible pavements in a variety of
base
reinforcement appli
catioos.
The techniques
are
equally applicable
to
major high
ways and small subdivisioo
roads.
Significant life cycle cost
savings can
be achieved with relatively little additional up
front expenditure.
Current
AASHTO
design methods exist to determine
appropriate pavement sectioos incorporating geogrids into
pavement structures. However, new and extremely innova
tive, state-of-the-art techniques using M-E principles are just
around the comer •
Courses
for Light Aircraft: Test Section Construction, Behavior
Under Traffic, Laboratory Tests and Design Criteria
Geotechnical Laboratory, Department
of
the Army,
Waterways Experiment Station, Corps of Engineers,
Mississippi.
References
• AASHTO 1993, AASHTO Guide For Design
of
Pavement
Structures, American Association of State Highway and
Transportation Officials.
• AASHTO, 2001, Provisional Standard PP46-01:
Recommended Practice For Geosynthetic Reinforcement of
the Aggregate Base
Course
of Flexible
Pavements
April 2001
Interim Edition.
Jim Penm an . CGeol . FG
S, d i
r('rlor
01 Ili.l\ial l'r()(lllrl,
'\l'l 'lirati"n'i I('f f,'n';.; f h l1
nnational
( ""fporation, i, a ;. ('okdmicri
,'n) i hw with n ll'[(' than
13
:l": f'
"xpni"n l'
" in tilt' ) ('o , :'ntlh't i
r,
li..ld . it- L ITI I", ,',HltMt", at ,il'(' ] nan(lI't
" I,afroq
',u) II I, Jo e
( "am
na u
g h , P.E. lite pre \ ident "I Ihhnol,,;. ; I, ' r len,ar
inte fllation<l i Corporat ion , i\ a re;. i-t(Tt'd t' l;. i lt'(T in
wHTal
,ta((',
and ha, ,.\ ;','<1" I'
"'I'er
it' lre in
;.
eowntl]('tit, and
) ,
'ornl lT1 ita i de\ i) lIitoll \
rruttion
. I it' t all lw t() ta
tlt'
d at
jra, <
;HJg
h(Ii',t('n\;
iT
' 1
1'
.('( lTI I.
• Perkins S.W. and Ismeik M., 1999, A
Synthesis
and
Professional Development Series
Sponsors:
' ~ A U l=f:t:l 9025 Centre Pointe Of.,
Suile
400.
West
Chester, OH 45069
~ ;; 'V ' t±i j (513) 645
-
7877
•
Fax: (513) 645-7993
•
Email:
info@lcontech<pi.com
EART H SUI l l lZATt ON
I 0 L U , I 0 • I I C
ensa[ Web: lWM'.conlech<pi.com
INlERNATIONAL
E
News's Professional Invelopment
Series
Reporting Fonn
Article Title: Exlending Flexible Pavement
life
Using Geogrids
SponSOr5: CONTECH Earth Sl3biliZ<ltion Solutions
I
nc., and
Tensar
Intemational Corporation
Publication Date:
Septembef
2006
V ~ l i d fOf credit
until:
Septembef
2007
Instructions
:
Select one a n s ~ r
for
each quiz question and
clearly
circle
the
appropriate letter.
Provide
all
of
the
requested
contact
information
,
Fax
this Reporting Form
to
(513) 64$.7993.
(You do not
need
to send the
Quiz; o n ~ this Reporting Form
s
necessary
to
be
submitted.)
I abc
d 6)
abc
d
2)
abc
d
7)
abc
d
3) a
b d 8)
a
b ( d
4)
a
b d 9)
a
b ( d
5) abc
d
10) abc
d
Required contact
information
Last
Name: First Name: Middle Initial:
Title:
Firm Name:
AddreS5:
City: State:
Zip:
Telephone:
Fax: E-mail:
Certification of ethical completion: Icertify that
t
read
the
article,
under5tood the
learning objectives,
and completed the quiz questions to
the
best
of
my ability.
A d d i t i o n a l ~
the contact information provided above
is
true
and accurate.
Signature:
Date:
Special Advertl$lng Section - CONnCH Earth Stabllllllion Solutlon$lnc./Ten$
ar
International Corp.
PO" 7
7/23/2019 Extending Flexible Pavement Life
http://slidepdf.com/reader/full/extending-flexible-pavement-life 8/8
Professional Development Series Quiz
Professional Development Series Sponsors:
~ ~ E C = = =
9025 Centre Pointe Dr., Suite 400, West Chester, OH 45069
t:t±:i (513)
645
-7877 • Fax: (513) 645-7993 • Email [email protected]
Web: W N W . c o n l e c h - q ) ~ . c o m
l i TH SU IH l l A r I O
Tensar.
•
I c
INTERNATIONAL
Quiz Instructions
On the
Professional
Development Series Reporting Form p<lge PDH 7 ,
circle
the correct answer for each
of
the fo llowing questions.
, . In base reinforcement applicatio ns (firm subgrade conditions),
what
is
the
main function of a geogrid in improving pave
ment
performance?
a) Enhance loild distribution
resu
lt ing in less vertical deflection o
the subgrade.
b) Reduce
la
tera l movemeot of aggregate particles within
the
base
co
urse
layer.
c) Prevent pumping
of
the subgrade.
d Reduce dynamic deflection of the asphalt.
2. Which of
the
following sets of index properties for a geogrid
would likely give
the
best indication of how
the
product
will
perform
in
roadway applications?
a) Ultimilte temile strength; aperture
size.
b) Tensile strength at 2% strain; percentage open area.
c) Aperture stability modulus (torsional rigidity); junction strength.
d) True
ini
t
ia
l modulus
in
use; creep limited strength.
3. Which of th e following are
~
s
ta t
e ments?
a) Geogrids can never provide effective separation between two
layers because
of
the passage of
fin
e mil through their apertures.
b) Geogrids and geotextiles essentia l
ly
use the 5ilme mechanisms
to provide reinforcement
c) The strength of the geogrid used
will
be the predominant factor
that determines the extension of design life for a reinforced pave
ment
d) None, all these statements are
fa
lse.
4.
Vl/hich
of the following is a ~ statement regarding the curre
nt
AASHTO (1993) pavement design approach?
a) l arge-scale trafficking studies conducted in the 1950s form the
basis for the design method.
b) The design approach is based primarily on theoretical predictions
of pavement performance.
c) Benefits of geog rids for base reinforcement are included in the
method.
d) NOlle, all of the above are false.
S. Based on
the
current AASHTO (1993) design approach, with all
other conditions remaining unchanged , what
wo
uld be the
effect of increasing
the subgrade
strength?
a)
An
increase in the overall Structural Number (SN) of the pave-
ment.
b) A li
kely
increase
in
the drainage properties of the pavement
c)
An
increase in the allowable traffic for the pavement.
d)
Al
l of the above.
6. Which of
the
following soil properties would
be
of
great
es t
value
to
an engineer when
de
signing a reinforced pavement on
a relative ly competent formation?
a) Shear strength of the subgrilde.
b
Shear strength
of
the base cou
rse.
c
Consolidation properties of the subgrade.
d) AJI equally valuable.
7. What difference(s) would you observe in
the
visual dist ress
between
s
ubgrade
rutting and base course rutting?
a) The
al
ligator cracks
will
be larger on the section
wi
th base
COUf5
e
rutting.
b The rut profile wil l be wider on the section wi th subgrade
rutting.
c
There is no difference, the rut profiles
will
be the same.
d) None of the above, as rutting always develops
in
both layef5
equally, and therefore you cannot determine the origin of the
rutting.
8. A subdivi sion road is characterized
by
alligator cracking
but
no
surface rutting. What is th e
most lik
ely
mode
of failure for
the
pavement?
a) Reflection of previous cracks caused by thermal expansion
contraction.
b Fatigue fai lure of the road as it reaches the elld of its design life.
c
Presence of a weak binder with in the asphalt.
d) All of the above are equally likely.
9. If
the
silty gravel subbase (overlying
the
subgrade,
and
supporting a dense-graded gravel base layer) is
the
critical
layer in a five-layer pavement section, where would you best
position
the
geogrid?
a) At the subbase-subgrade interface.
b In the middle of the subbase layer.
c At
the subbase-base interface.
d)
Any of the above, because the geog rid
wi
ll provide the same
contributio n at al l three locations.
10. Which of
the
following advantages apply
to
Mechanistic
Empirical design methods compared with the purely empirical
approach currently
adopted
by AASHTO?
a) Designs can account for
va
riations in material properties with
time.
b
The approach can more easily be adapted
to
take account
of
local mil and climatic conditions.
c
Design methods adopted now
will
more easily adapt to changes
in
ve hicl
e ioads
in
the future
as
trucks develop.
d) All of the above.
OPOH
Spedal
Advertising Section - CONTECH Earth Slablizallon Solutlon$ Inc./Ten5M Inlemallonal Corp.