Use of Geogrids in Railroad Applications

8/14/2019 Use of Geogrids in Railroad Applications

1/12

The Use of Geogrids

in Railroad ApplicationsBy Jim Penman, CGeol, FGS, and Daniel J. Priest, P.E.

OCTOBER 2009


2/12

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The inclusion of geogrids

within the unbound aggre-

gate layers of unpaved and

paved road structures has

become increasingly common since the

products were first introduced more

than 25 years ago. However, there is

less awareness within the engineering

community that the same technol-

ogy is equally applicable to roadbed

structures in rail applications. The use

of geogrid reinforcement in the sub-

ballast and ballast layers of roadbed

sections has gained widespread accep-

tance in many parts of the world. For

example, national rail authorities in

some European countries have gone

so far as to provide formal guidance on

the use of these materials in their own

design codes. More recently here in

the United States, formal guidance on

the use of geogrids in rail applications

has been provided by the American

Railway Engineering and Maintenance-

of-way Association (AREMA).

This article is intended to provide

the background information neces-

sary to design roadbed structures that

include geogrids within the sub-ballast

and/or ballast layer. Reference will be

made to the extensive research that

has been undertaken during the last

20 years to quantify the performance

benefits associated with the use of

geogrids in this application. An addi-

tional section will describe the means

by which geogrids can provide simi-

lar benefits in the heavily loaded road

structures surrounding the rail tracks at

intermodal facilities.

Geogrid reinforcementmechanisms

A geogrid is defined as a

geosynthetic material consisting

of connected parallel sets of tensile

ribs with apertures of sufficient size

to allow strike-through of surround-

ing soil, stone, or other geotechni-

cal material (Koerner, 1998). When

unbound aggregate is placed on top

of the geogrid, the coarser particles

partially penetrate through the aper-

tures and lock into position (Figure

1). This effect, commonly referred to

as mechanical interlock, leads to lateral

The Use of Geogridsin Railroad ApplicationsBy Jim Penman, CGeol, FGS, and Daniel J. Priest, P.E.

Figure 1: Mechanical interlock of aggre-gate with a geogrid

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Learning ObjectivesAfter reading this article you should understand:

How including geogrids within ballast and/or sub-

ballast layers can enhance the performance of road-bed structures

The value provided by including geogrid reinforce-

ment in rail applications

The design methods available for geogrid reinforced

roadbed structures

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4/124 PDH Professional Development Advertising Section CONTECH Construction Products Inc.

The Use of Geogrids in Railroad Applications

confinement of the

unbound aggregate

and a general stiffening

of the layer.

The confining effect of a geogrid

is especially important in a roadbed

reinforcement application, as lateralmovement of granular particles is a

major cause of sub-ballast and ballast

settlement. However, the stiffening

effect is also important, particularly

when construction takes place on a

less competent subgrade (stiff clay or

worse). Under these circumstances, the

stiffer aggregate distributes load more

efficiently onto the underlying soil,

thereby reducing both the dynamic

movement (vertical track deflection

during a single load cycle) and the

longer term settlement of the roadbed

due to subgrade consolidation.

Previous research andfield studies

The earliest research undertaken to

quantify the benefits of using geogrids

as reinforcement within a roadbed

structure was carried out at Queens

University in Kingston, Ontario, by

Bathurst and Raymond (1987). An arti-

ficial subgrade (consisting of a series of

rubber-bonded cork mats) was placedat the bottom of a rigid test box. The

remainder of the box was filled with

ballast. Cyclic loads generated by a

hydraulic actuator were applied to a

cross-tie placed on the surface of the

ballast (Figure 2).

The results of the testing (Figure 3)

show how for a maximum limit of 25

mm (1 inch) of permanent settlement,

the presence of a geogrid within the

roadbed extended its service life. An

almost five-fold increase is indicatedfor cases where both a reasonably

competent subgrade is used (CBR of

39) and where a soft subgrade condi-

tion exists (CBR of 1).

In a further study reported by

Matharu (1994), a set of full-scale tests

were undertaken at the British Rail

(now called Network Rail) test facil-

ity located in Derby, England (Figure

4). The main results from the study

(Figure 5) effectively show that when

Figure 2: Cyclic loads are applied to across-tie placed on the ballast surface atQueens University.

Figure 4: Network Rail test facility in Derby,England

Figure 3: Results of cyclic load tests at Queens University.

Figure 5: Full-scale tests show that the rate of settlement for a roadbed constructed ona soft subgrade but reinforced with a geogrid is similar to that of the same roadbedconstructed on bedrock.



a roadbed reinforced with a geogrid is

constructed on top of a soft subgrade,

its rate of settlement is similar to that of

the same roadbed section constructed

on bedrock. In addition, the dynamic

vertical movement occurring in the

track as the wheel of the train passes isreduced by approximately 40 percent

when a geogrid is used to reinforce

the roadbed (Figure 6).

A rail corridor constructed between

Hochstadt and Probstzella in Germany

(Figure 7), presented an opportu-

nity to observe the benefits of using

geogrids in a full-scale field situation.

Plate bearing tests undertaken by the

German rail authority (Deutsche Bahn)

demonstrated that the stiffness of a

400-mm-thick (16-inch-thick) sub-

ballast was approximately the same as

a 600-mm-thick (24-inch-thick) unre-

inforced section. Also, the stiffness of

both 400-mm (16-inch) and 600-mm

(24-inch) sections doubled when a

geogrid was included (Figure 8).

On a similar project constructednear Cologne, Germany, inclusion of a

geogrid within a roadbed constructed

over a soft formation allowed the sub-

ballast to be reduced from 1,050 mm

(42 inches) to 700 mm (28 inches).

Despite the thickness reduction, the

target modulus of 120 MPa (17,400

psi) was maintained.

On a mainline project in Nagykanizsa,

Hungary, the decision was made to

include a geogrid within the ballast

layer during a rehabilitation operation.

Prior to replacement of

the existing roadbed,

the rail line required

monthly re-surfacing

maintenance. The dynamic deflection

of the rail track was measured using

a rail car, both prior to and follow-

ing the inclusion of the geogrid within

the roadbed section (Figure 9). As can

be seen, the inclusion of the geogrid

resulted in a dramatic reduction in the

dynamic deflection taking place during

trafficking. Service disruptions due to

the requirement for frequent mainte-

nance have since been eliminated.

Previous experienceThere are more than 100 projects

where geogrids have been used to rein-

force the sub-ballast or ballast layers

within a roadbed structure. All of the

U.S. Class 1 rail companies have used

geogrids within their roadbed struc-

tures at one time or another and several

light/passenger rail companies also have

experience in the use of these products.

Following are summaries about a select

number of these projects.

Utah Transit Authority (UTA)

Light Rail Project, Salt Lake

City (2005-2008) The UTAs

FrontRunner commuter rail line runs44 miles from the city of Ogden in

Weber County south to Salt Lake City.

The line is located in an existing right-

of-way that runs parallel with the

Wasatch Mountains. The area is part

of a natural drainage basin, character-

ized by poor quality soils and shallow

groundwater. The subgrade beneath

the roadbed typically consisted of low-

Figure 6: Geogrid reinforcement in the roadbed reduces dynamic vertical movement in thetrack by about 40 percent as the wheel of a train passes.

Figure 7: A rail corridor between Hochstadtand Probstzella, Germany, enabled obser-vation of the benefits of using geogrids ina full-scale field situation.

Figure 8: In German tests, the stiffness of a 400-mm-thick (16-inch-thick) sub-ballast wasapproximately the same as a 600-mm-thick (24-inch-thick) unreinforced section.




to medium-strength

cohesive soils and

loose to dense sand.

A conventional roadbed

design, consisting of a thicker sub-

ballast layer, proved cost prohibitive

because of the extremely high costassociated with the sourcing of local

aggregate. Calculations determined

that the required sub-ballast thick-

ness could be conservatively reduced

from 12 inches to 8 inches by includ-

ing a layer of geogrid at the inter-

face between the sub-ballast and the

underlying subgrade. Reducing the

sub-ballast depth provided signifi-

cant cost savings and expedited the

construction process less aggregate

could be placed in less time. In addi-

tion, this approach eliminated contact

with the shallow groundwater and the

need to relocate the existing buried

utilities for 900 feet of track.

Dallas Area Rapid Transit

Authority (DART), NW1A Rail

Section, Dallas (2003-2008)

DART has regularly used geogrids

within its roadbed sections since

2003. Traditionally, prior to construct-

ing its standard roadbed section, the

underlying cohesive soils would first

be mixed with lime to a depth of 6inches. Although this provided good

short-term support for the roadbed,

this approach resulted in some logisti-

cal problems.

Installation of the lime stabilization

was not well suited for the project

because of the generation of extensive

dust clouds in the urban project loca-

tion. Additionally, the lime stabilization

installation process requires dry, mild

weather conditions. Finally, protrud-

ing utility pipes were present at thetime the roadbed was constructed

(Figure 10). Since large vehicles are

required to install the lime, this would

have made things very difficult for the

contractor and slowed the construc-

tion process down significantly.

To provide an alternate solution

to the lime stabilization, a structural

analysis was undertaken to demon-

strate that the 6 inches of lime treat-

ment could be avoided by including a

layer of geogrid at the bottom of the

standard roadbed section. Installation

adopting this mechanical stabiliza-

tion technique was both simple and

fast, requiring only minor slitting of

the geogrid in the areas where the

protruding utilities were located.

Kansas City Southern Rail

(KCSR) Company, Victoria to

Rosenberg Line, Texas (2008)

During 2008 and early 2009, KCSR

undertook reconstruction of a 91-mile

section of former track in south Texas.

Where weaker subgrades were encoun-

tered or the original sub-ballast had

been removed or washed out, normal

construction methods required place-

ment of as much as 12 inches of new

sub-ballast. Instead, a geogrid was

placed at the bottom of the new sub-

ballast to reduce the required thick-

ness to only 6 inches (Figure 11).

With no local suppliers, sub-ballast

aggregate was transported from

quarries in Hatton, Ark., and Mexico,

resulting in a particularly high cost

for the installed material . On this

project, reducing the required sub-

ballast thickness resulted in significant

construction cost savings. In total,

approximately 237,000 square yards

of geogrid was installed.

Figure 9: Dynamic deflection of rail track measured using a rail car, both prior to andfollowing the inclusion of geogrid within the roadbed section.

Figure 10: Utility pipes protruding from a Dallas Area Rapid Transit Authority roadbed areaccommodated by minor slitting of the geogrid.



Geogridreinforcedroadbed structures

The U.K. Approach

to design In the United Kingdom,

the national rail authority, Network

Rail, has been using geogridsbeneath its main line tracks since

the early 1990s. In addition, it has

undertaken several in-house test-

ing programs, both in the laboratory

and along in-service tracks, to quantify

the performance benefits associated

with the use of geogrids in roadbed

structures.

Design protocols for roadbed

structures are prescribed in Network

Rail (2005). The general approach

adopted is to attain a target stiffness

for the roadbed beneath the track. As

shown in Table 1, this value varies and

depends on whether or not a geogrid

is included within the roadbed struc-

ture a minimum dynamic sleeper

support stiffness (K) of 60 kN/mm is

required for an unreinforced roadbed,

whereas only 30 kN/mm is required

for the same acceptable level of perfor-

mance when a geogrid is included

within the roadbed section.

For a given set of subgrade condi-

tions and the same type of aggregate,the stiffness of a roadbed section is

essentially a function of the thickness

of the ballast and sub-ballast layers. As

indicated in the design chart shown in

Figure 12, the use of a geogrid results

in a thickness reduction for the roadbed

of around 8 inches (200 mm) relative

to a conventional unreinforced section.

It should be appreciated that

although the Network Rail design proto-

cols refer to geogrids generically no

specific manufacturers products areruled in or out any geogrid product

proposed for use on its system requires

a current PADS Certificate. This docu-

ment is obtained from Network Rail and

is only issued for products where the

performance benefits prescribed above

have been demonstrated in full-scale

laboratory and field tests. It is not suffi-

cient simply to offer an equivalent prod-

uct based on material properties, even

if these properties exceed those for a

Figure 11: Geogrid placed at the bottom of a roadbed in Texas reduced the required thick-ness of sub-ballast by 50 percent.

TABLE 1: Target roadbed stiffness

Minimum Dynamic Sleeper Support

Track Condition Stiffness, K (kN/mm/sleeper end)

Absolute Value 30

Existing Main Lines

With Geogrid

Reinforcement 30

Without Geogrid

Reinforcement 60

New Track Up to 100 mph 60

Above 100 mph 100

Figure 12: Network Rail design chart for determining the required roadbed thickness.




product with an exist-

ing PADS Certificate. To

date, only stiff geogrids

with integral junctions have

obtained PADS certification.

The U.S. approach to design

In the United States, most of the freightand passenger rail companies have

standard roadbed sections for their rail

systems. When particularly unfavorable

soil conditions are encountered, extra

subgrade improvement measures may

be taken including over-excavation

and replacement, chemical treatment,

placement of an asphaltic layer at the

bottom of the roadbed section, etc.

Geogrids are also commonly used in

these circumstances, though in many

cases, a detailed analysis and design is

not necessarily undertaken.

When a more rigorous roadbed

design is conducted, the approach

originally developed by Professor

Arthur Newell Talbot at the University

of Illinois is still the method of choice

for many rail engineers. Although it is

based on research undertaken toward

the early part of the last century, the

Talbot method is still listed in the

current AREMA (2009) design manual.

The basic Talbot equation is defined

in Equation1:

where,

h = required thickness of ballast plus

sub-ballast below the ties (inches);

pc= allowable stress at depth hunder

cross-tie centerline (pounds per square

inch (psi)); and

pa= imposed pressure at face of cross-

tie (psi).

The parameter pa is determined

using Equation 2.

where,

IF = impact factor (function of wheel

diameter and maximum train

speed);

DF= distribution factor; and

A= surface area of cross-tie face

(square inches).

Given that this methodology was

developed almost half a century

before the first geogrids were

invented, it is not surprising that thereis no prescribed means to include the

benefits provided by these materi-

als. However, as mentioned previ-

ously, it is widely accepted that one

of the principle functions of a geogrid

is to stiffen an aggregate layer and

thereby provide a more efficient

means by which to transfer load onto

the underlying subgrade. If then,

based on full-scale testing, it can be

determined what these load-spread

benefits are for a particular geogrid

product, the allowable stress param-

eter (pc) in Equation 1 can be adjusted

accordingly. A decrease in the pres-

sure imposed at the subgrade level

would clearly lead to a reduction in

the required roadbed thickness.

Although, up to this point, no formal

guidance has been provided by AREMA

on the use of geogrids in roadbed

structures, a new section describing the

benefits associated with the use of these

products has recently been approved for

publication and will appear in the 2010edition of the AREMA design manual.

This new section will also include

details on how to specify geogrids in

this particular application.

Ballast life extensionIn the United States, geogrids are

most commonly used within the sub-

ballast layer to reduce the required

thickness of the roadbed. In some

cases, a detailed design is under-

taken in accordance with the proce-dures outlined above. In other cases, a

geogrid is simply added at the bottom

of a standard roadbed section to effec-

tively beef it up. Either way, the

issue being addressed by the use of a

geogrid is one associated with poten-

tial instability or excessive settlement

of the subgrade.

In mainland Europe, inclusion of a

geogrid at the bottom of the ballast

layer is a more common practice. Under

these circumstances, the principle

benefit provided by the geogrid is one

of service life extension. Although this

approach results in an increase in the

initial cost of the roadbed section or the

rehabilitation costs for an existing road-

bed structure, the ballast life extensioncan easily outweigh this initial invest-

ment. Based on the laboratory and field

testing undertaken to date, it is likely

that a three- to five-fold increase in the

life of the ballast will be attained when a

geogrid is included within this layer.

Heavy-duty pavementstructures

The loading and unloading area

around the rail tracks at intermodal

facilities and in industrial yards can

provide significant challenges to pave-

ment designers. The applied loads

from container stacking equipment are

extremely high. Even when relatively

firm subsoil conditions exist, these

loads can lead to excessive movement

of the base course and cracking of

asphaltic layers. Geogrids can be used

in these structures to help reduce or

eliminate these problems.

When soft soil conditions are

encountered, an initial layer of aggre-

gate is frequently placed prior toconstruction of the main pavement

structure. When a geogrid is used

within this layer, the required thick-

ness can generally be reduced by 50

percent to 60 percent. Full details

of this application and the design

methodology associated with it are

provided by Archer (2008).

When good quality subsoil condi-

tions exist, a geogrid can also be

included to enhance the performance

of the main pavement structure.Up-front construction cost savings can

be attained by reducing the required

thickness of the unbound aggregate

and/or asphaltic layers in flexible pave-

ments. Recent research has shown

that some of the newer geogrids can

achieve a thickness reduction of as

much as 50 percent in the aggregate

layer or 30 percent in the asphalt layer.

The long-term stiffening of the aggre-

gate layer can also be used to provide

(Equation 2)

(Equation 1)



component reductions in rigid pave-

ment structures.

Alternatively, when life cycle cost

savings are considered more impor-

tant, geogrids can be used to extend

the life of a pavement structure.

Numerous full-scale tests have beenundertaken to quantify the extension

of life provided by geogrids in flexible

pavement structures. Typically, a three-

to six-fold increase can be expected

for the better quality geogrid products

currently available. A detailed descrip-

tion of the topic of pavement life exten-

sion in geogrid reinforced pavement

structures is provided by Penman and

Cavanaugh (2006), and further details

on how to quantify the benefits of

using geogrids in pavement structuresare provided in AASHTO (2001).

Installation considerationsFor sub-ballast reinforcement appli-

cations, or where a geogrid is to be

included within a

pavement structure,

the method of installa-

tion is straightforward. If

possible, the existing surface is graded

and crowned to promote positive

drainage away from the main areaof trafficking. Any protruding objects

such as tree stumps are removed prior

to rolling out the geogrid. Overlaps of

1 foot to 3 feet are generally sufficient

to ensure that full geogrid coverage is

maintained during the design life of the

structure. Only when extremely soft

conditions are encountered is it neces-

sary to peg or tie geogrids together.

Once the geogrid has been rolled

out, the overlying aggregate can

be placed and compacted immedi-

ately. Conventional dump trucks and

compaction equipment can be used

provided the underlying subgrade

has sufficient strength to carry the

imposed loads.

For ballast reinforcement applica-

tions, special provision needs to be

made because of the clean, coarse

nature of the aggregate generally used

for this layer. Under normal circum-

stances, trafficking with heavy-axle

trucks on a limited thickness of aggre-

gate underlain by a geogrid is not aproblem. However, in the case of a

ballast stone, the lack of a finer frac-

tion can result in shoving and exces-

sive rutting at the surface even after a

fairly limited number of vehicle passes.

For a relatively thin ballast layer, the

geogrid can be exposed and pulled

up during the installation process.

Therefore, truck trafficking must be

limited when a geogrid is included

within the ballast layer.

Limiting the amount of truck traf-ficking can be achieved in the follow-

ing ways: Use an access road along the side of

the rail line so the trucks can drive

on and off the track area only where

they are dumping aggregate. If an existing track is located adja-

cent to the track being constructed,

side dump aggregate from trains. Once the geogrid is placed directly

on the sub-ballast, the track can be

Figure 13: Geogrid is rolled out by a track-mounted undercutting machine prior to newballast being dropped in place.

REFERENCES

AASHTO, 2001, Recommended Pract ice for Geosynthetic Reinforcement of the

Aggregate Base Course of Flexible Pavements, American Association of State Highwayand Transportation Officials Provisional Standard PP46-01.

Archer, S., 2008, Subgrade Improvement for Paved and Unpaved Surfaces UsingGeogrids, CE NewsProfessional Development Series, October 2008.

AREMA, 2009, Manual for Railway Engineering, American Railroad Engineering andMaintenance-of-way Association.

Bathurst, R.J and Raymond, G.P., 1987, Geogrid Reinforcement of Ballasted Track,Transportation Research Board 66th Annual Meeting

Koerner, R.M., 1998, Designing with Geosynthetics, fourth edition, Prentice Hall,

Upper Saddle River, NJ.

Matharu, M., 1994, Geogrids Cut Ballast Settlement Rate on Soft Substructures,Railway Gazette International, March 1994.

Network Rail, 2005, Formation Treatments, Business Process Document NR/SP/

TRK/9039.

Penman, J. and Cavanaugh, J., 2006, Extending Flexible Pavement Life UsingGeogrids, CE NewsProfessional Development Series, September 2006.


10/12


constructed directly

on top. Ballast cars can

then be used to place

aggregate before lifting the

track and compacting with conven-

tional vibrating tines.

When ballast is being placedmechanically (for example, using

a track-mounted undercutting

machine) the geogrid can easily be

installed as part of this process. A

simple modification is undertaken

to the underside of the machine

(Figure 13) and the geogrid is rolled

out immediately prior to the new

ballast being dropped into place.

SummaryThe use of geogrids to enhance

the performance of roadbed sections

has become much more widespread,

particularly during the last 10 years.

Initial cost savings on the order of

$30,000 per linear mile of track can

generally be achieved by installing a

geogrid within the sub-ballast layer and

reducing the overall roadbed thickness.

Alternatively, by including a geogridwithin the ballast layer, the period

between maintenance events can be

extended by a factor of three to five.

For heavy-duty pavement structures

at intermodal facilities and in indus-

trial yards, geogrids can be used on

soft soils to reduce by 50 percent to

60 percent the amount of aggregate

required to provide a stable platform on

which to construct the main pavement

structure. In addition, geogrids can be

used within the pavement structure

to reduce the thickness of the aggre-

gate layer by as much as 50 percent

and the thickness of the asphalt by as

much as 30 percent without a reduc-

tion in structural capacity.

Jim Penman, CGeol, FGS, direc-

tor of business development for TensarInternational Corp., is a geotechnical

engineer with more than 15 years experi-

ence in geosynthetics. He currently serves

on AREMA Committee 1 (Roadway

and Ballast) and can be contacted at

[email protected].

Daniel J. Priest, P.E., product

manager Road Solutions for CONTECH

Construction Products Inc., holds a

MSCE from Northwestern University

and has more than 10 years of experi-

ence in the geosynthetics industry and

geotechnical engineering. He can becontacted at [email protected].

10 PDH Professional Development Advertising Section CONTECH Construction Products Inc.

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1. The primary reinforcing mechanism for geogrids in

the reinforcement of roadbed structures is:

a) Tensioned Membrane Effect

b) Improved Bearing Capacity

c) Lateral Restraint through Mechanical Interlock

d) Tensile Resistance at low strain

e) All of the above

2. The confining effect of a geogrid:

a) Reduces lateral movement of the granular particles

b) Stiffens the aggregate

c) Helps distribute the applied load more efficiently

d) Helps reduce the long-term settlement of the

roadbed structure

e) All of the above

3. Research conducted by Network Rail determined that

a geogrid reinforced roadbed has:

a) A 40-percent reduction in the dynamic vertical

movement

b) More settlement than an unreinforced section

c) An increase in the subgrade modulus

d) Less stiffness than a comparable unreinforced section

e) All of the above

4. A full-scale field simulation by Deutsche Bahn

concluded that:

a) The stiffness of a 16-inch reinforced section was

approximately equivalent to that of a 24-inch

unreinforced section

b) The stiffness of a 16-inch reinforced section was

double that of a 16-inch unreinforced sectionc) Geogrid inclusion had no effect on the stiffness of a

24-inch thickness of ballast stone

d) a and b

e) All of the above

5. Which of the following statements are true with

respect to the design method developed by Network

Rail?

a) The maximum thickness reduction provided by a

geogrid is 4 inches

b) A reduction in the required thickness of the roadbed

is based on the additional roadbed stiffness resultingfrom confinement of the aggregate by a geogrid

c) All geogrids essentially perform the same and

therefore any geogrid can be used with the Network

Rail design method

d) Geogrids can only be used to reduce the required

roadbed thickness when the subgrade is soft

e) All of the above

6. The Talbot equation in the AREMA Manual for Railway

Engineering:

a) Is based purely on mechanistic principles

b) Was developed based on research

undertaken at the University of Iowa

c) Helps determine the required thickness

of the roadbed

d) Predicts the vertical settlement occurring beneath the

track structure for a given amount of trafficking

e) None of the above

7. How can geogrids be accounted for in a design

incorporating the AREMA (Talbot equation) design

method?

a) The imposed pressure at the face of a cross-tie is

reduced by a factor of 4

b) The distribution factor component of the equation

used to determine the parameter pais doubled

c) The allowable stress component (pc) in the equation

is adjusted to account for the presence of the geogrid

d) The unreinforced roadbed thickness is simply reduced

by 20 percent

e) They cant be accounted for since geogrids were not

invented when the Talbot equation was developed.

8. Geogrid inclusion beneath the ballast stone can:

a) Mitigate potential instability

b) Prevent excessive settlement

c) Provide a three- to five-times increase in ballast

service life

d) a and c

e) a, b, and c

9. Inclusion of a geogrid within a heavy pavement

structure will:a) Provide no benefit to the structural capacity of the

pavement

b) Provide a maximum of double the service life of the

pavement

c) Allow for the reduction of asphalt thickness by as

much as 30 percent without a reduction in service life

d) Allow for the reduction of aggregate thickness by

a maximum of 30 percent without a reduction in

service life


10. During installation of the sub-ballast and ballastwhen a geogrid is to be included:

a) Conventional equipment and compaction methods

can be utilized

b) Special equipment should be utilized to ensure the

geogrid is not damaged

c) Truck trafficking should be kept off of the section at

all times

d) Mechanical ties are always required to prevent two

adjacent lengths of geogrid pulling apart


Professional Development Series Quiz

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Use of Geogrids in Railroad Applications

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