PRS-Neoweb™

for Railway Track Reinforcement

PRS-EN-TD-LS-2002 Rev. 13.01

TECHNICAL OVERVIEW

www.prs-med.com

© 2013 Copyright and Proprietary of PRS. Certain products and/or applications described or illustrated are protected under international patents. Final suitability of any information or material for use and its manner of use is the sole responsibility of the authorized user.

PRS-EN-TD-LS-2002 2/17 Rev. 13.01

Contents

GENERAL DESCRIPTION .............................................................................................................................. 3

Railway Operations & Maintenance ...................................................................................................... 3

PRS-Neoweb™ Reduces Track Maintenance ........................................................................................... 3

NEOLOY® POLYMERIC ALLOY STRENGTH .................................................................................................... 4

PRS-NEOWEB RAILWAY SOLUTIONS .......................................................................................................... 5

PRS-Neoweb in Ballast Layer Prevents Ballast Attrition ........................................................................ 5

Increase Bearing Capacity of Subballast Layer ....................................................................................... 5

BENEFITS OF NEOLOY-BASED PRS-NEOWEB .............................................................................................. 6

RESEARCH ON NEOLOY-BASED PRS-NEOWEB ........................................................................................... 7

PRS Worldwide Collaborative R&D Program ......................................................................................... 7

Research Results - PRS-Neoweb vs. HDPE Geocells ............................................................................... 7

NEOLOY-BASED PRS-NEOWEB SPECIFICATIONS ........................................................................................ 9

Evolving Standards for Geocells ............................................................................................................. 9

DIMENSIONAL STABILITY – Cell Ability to Withstand Thermal (Temperature) Cycling............................ 10

SIM Accelerated Creep Test & Tensile Strength ...................................................................................... 11

FLEXIBLE STORAGE MODULUS – Performance at Elevated Temperatures .............................................. 11

OXIDATION RESISTANCE (OIT) – Long Term Reliability of Polymer .......................................................... 13

PHOTOCHEMICAL (UV) RESISTANCE (HPOIT) ........................................................................................... 13

APPENDIX – SUMMARY OF RESEARCH ..................................................................................................... 14

PRS-Neoweb Railway Embankments – Maintaining Ballast Geometry (Leshchinsky, B., Ling, H., et al,

Columbia U., USA) .............................................................................................................................. 14

Contribution to Pavement Reinforcement (Rajagopal, et al, Indian Institute of Technology, Madras,

India and Kief, PRS) ............................................................................................................................. 14

Geogrid Trial Road Base (Van Gurp, Westeral, KOAC-NPC Institute, Holland) .................................... 15

PRS-Neoweb Base Reinforcement Research and Full Scale Trafficking Testing - (Han J. et al,

University of Kansas, USA) ................................................................................................................. 15

Bearing Capacity Improvement in Road Constructions (Meyer, N., et al, Clausthal University,

Germany) ............................................................................................................................................ 16

Earth Retention – Seismic Research (Leshchinsky, D., et al, University of Delaware, USA) ................. 17

Field Demonstration of PRS-Neoweb in Amtrak Track Substructure for High Speed Passenger Rail

Operations .......................................................................................................................................... 17

PRS-EN-TD-LS-2002 3/17 Rev. 13.01

GENERAL DESCRIPTION

Railway Operations & Maintenance

Track maintenance is necessary for the integrity, functionality and safety of the track and right of way

and essential for safe and efficient operation of railways. Whereas track surface (geometry) degrades

under traffic, the rate of degradation is a function of annual traffic density, axle load, speed. These

factors are very sensitive to the track substructure and support conditions, and are critical for high

speed passenger operations (particularly when combined with heavy axle load freight service) and in

locations with poor subgrade and/or ballast conditions. Track geometry degrades rapidly resulting in

the need for frequent expensive surfacing, ballast cleaning, and related maintenance activities.

Three-dimensional PRS-Neoweb cellular confinement system technology (geocells) provides

reinforcement to the substructure and structural support in railroad track. PRS-Neoweb usually placed

at the ballast/subgrade interface area has been shown to decrease the rate of track surface geometry

degradation (both surface and cross-level) under a range of traffic loadings. The ability of PRS-Neoweb

to reduce the rate of degradation, particularly in these high degradation rate locations, is of great

value for both in the construction of new lines and in the maintenance of existing lines (Zarembski,

2011, internationally recognized railway authority).

PRS-Neoweb™ Reduces Track Maintenance

This increased performance, however, is dependent on the type of geocell utilized. Recent research

in cellular confinement systems demonstrates that not all geocells are equal. Only PRS-Neoweb based

on the Neoloy novel polymeric alloy has a high elastic modulus that significantly increases the

stiffness, bearing capacity, stress distribution and reduces deformation, as compared to HDPE geocells

(See section on Specifications). Leshchinsky, D. (2009) stated in a major research study “However,

without improvement, HDPE geocells are not suitable for long-term applications.”

The use of PRS-Neoweb high-strength geocells as a structural support element at the ballast/subgrade interface can reduce surface geometry degradation. Laboratory and full scale field testing under a range of conditions confirmed that the Neoloy-based PRS-Neoweb decreased the rate of track surface geometry degradation (both surface and cross- level) by a factor of 2-2.75 and higher. This range is validated by PRS-Neoweb research in the base reinforcement of roads (see Summary in Appendix).

PRS-Neoweb reinforced track substructure

significantly increases the intervals between

track geometry maintenance cycles (intervention

and tamping cycles) and associated cost savings.

This is due to the increased surfacing cycle

(reduced number of tamping operations required

over the time) and avoided train delay costs. PRS-Neoweb with Neoloy maintains its engineering

characteristics and geometry under millions of dynamic loading cycles unlike HDPE geocells, thereby

reducing railway operational and maintenance cost requirements. In fact, the cost of maintaining

such infrastructure over time (Total Cost of Ownership) determines the economic worthiness and

success of the track engineering solution and not the initial construction cost.

PRS-EN-TD-LS-2002 4/17 Rev. 13.01

NEOLOY® POLYMERIC ALLOY STRENGTH

The materials used in manufacturing geocells are extremely important in order to enhance the confinement effects and to ensure that they last for the duration of the project. PRS-Neoweb from Neoloy, a novel polymeric alloy, is the only high-modulus geocell that was specifically designed for very heavy ground reinforcement.

Neoloy is an innovative high-strength polymeric alloy developed by PRS for the PRS-Neoweb cellular confinement system. Based on nano-fibers in a polyolefin matrix, Neoloy combines the ductility of HDPE with the dimensional stability and creep resistance of polyester. Neoloy-based PRS-Neoweb is manufactured in a patented process in multi-layer strips: a high strength inner core layer is sandwiched between two high durability outer layers to provide optimal performance – strength, rigidity, and chemical stability.

This unique material provides PRS-Neoweb geocells with unrivaled long-term resistance to: creep,

fatigue, stress-cracking, temperature extremes, oxidation and UV light. In addition Neoloy is a non-

corrosive, inert engineering thermoplastic resistant to external environmentally harsh conditions,

wind and dust and water. Special additives and manufacturing processes make PRS-Neoweb highly

resistant to UV radiation. The performance parameters of Neoloy-based PRS-Neoweb are described in

the section on specifications.

PRS-Neoweb with Neoloy maintains its engineering characteristics and geometry for the project

lifespan. PRS-Neoweb has been successfully deployed in all type of environments from desert sands

(Kazakhstan, Afghanistan), to peat bogs (Ireland, Canada) to the arctic tundra (Russia, Siberia).

PRS-EN-TD-LS-2002 5/17 Rev. 13.01

PRS-NEOWEB RAILWAY SOLUTIONS

PRS-Neoweb offers cost-effective ground reinforcement solution for subballast and ballast layers, rail

embankments, turnouts and yards. The PRS-Neoweb confinement mechanism makes the

geocell/ballast composite very stiff, strong and durable. This minimizes lateral and vertical

deformation in the track substructure. Studies have shown that PRS-Neoweb can triple the carried

load without excessive vertical deformation (Leshchinsky, B., et al, 2010).

PRS-Neoweb in Ballast Layer Prevents Ballast Attrition

A main reason for maintenance of track is ballast settlement. Unconfined ballast spreads laterally,

allowing for settlement. In addition the relative movement of ballast particles under high cyclical

loading from rolling stock is the major cause of ballast degradation. This attrition is due to abrasion as

well as breakage of the aggregate particles. The result is weak, poorly draining ballast.

PRS-Neoweb confinement of the ballast layer increases its stiffness and restrains its lateral movement.

This prevents shearing of aggregate under loading. Rigidity of the infill and cell walls is increased by

the developed cell wall hoop stresses as well as by passive resistance from surrounding cells.

The stiff confinement provided by Neoloy based PRS-Neoweb minimizes the relative movement of

particles, reduces aggregate abrasion and attrition, thereby preventing degradation in track geometry.

Increase Bearing Capacity of Subballast Layer

PRS-Neoweb strengthens the track substructure layer underneath the ballast and prevents

degradation of the rail embankments by creating a stiff mattress (semi-rigid platform). The PRS-

Neoweb system behaves more like a three-dimensional semi-rigid slab or beam. The high shear

strength and greater load distribution of PRS-Neoweb reduce the vertical stresses to the subgrade.

The increased bearing capacity of the subgrade strengthens the subballast layer and reduces

settlement and accumulated degradation, thereby preventing deformation of the rail embankments.

Lower quality infill can be utilized in place of expensive well-graded subballast aggregate, while the

thickness of the subballast layer can be reduced by up to 50% with no reduction in structural strength.

The long-term performance of the substructure under the ballast layer is critical as it is not subject to

regular maintenance.

PRS-EN-TD-LS-2002 6/17 Rev. 13.01

BENEFITS OF NEOLOY-BASED PRS-NEOWEB

Engineering Benefits

Trackbed stabilization – PRS-Neoweb confinement alters physical and mechanical properties of the trackbed. Ballast life is extended by reducing lateral displacement, vertical settlement and aggregate attrition.

Very durable polymer – Neoloy based PRS-Neoweb stiffness, dimensional stability and creep resistance under loading, stress and extreme environmental conditions preserve track geometry.

Reduce layer thickness – structural strength of PRS-Neoweb enables a significant reduction of the sub-ballast layer, thereby reducing aggregate and construction costs.

Use local infill – PRS-Neoweb can utilize local, inferior, and recycled infill material for sub-ballast.

More effective than geogrids – 3D PRS-Neoweb does not require specific high grade aggregate, while offering a larger zone of influence.

Operational Benefits

Easy and fast deployment – all-weather, simple logistics and fast installation minimize downtime.

Improved performance – stabilized substructure reduces substructure vibrations, track deflection, and enables smooth transitions between areas with differing subgrades.

Improved rolling stock performance – Studies show that PRS-Neoweb reinforcement can enable up to 40% heavier loads to travel up to 30% faster on the same track infrastructure.

Economic Benefits

Sustainable – reduced infill requirements preserve quarry resources, utilize regional materials, lower hauling expenses and cut the carbon footprint.

Operating expenses – stabilized rails significantly reduce vibration, wear and tear on rolling stock (as well as aggregate), thereby extending service life and reducing equipment maintenance.

Cost effective – saves time, equipment, and resources during the initial construction phase, while long-term durability extends track maintenance by a factor of 2-3x (perpetual superstructure), guaranteeing a low total cost of ownership.

PRS-EN-TD-LS-2002 7/17 Rev. 13.01

RESEARCH ON NEOLOY-BASED PRS-NEOWEB

PRS Worldwide Collaborative R&D Program

The extensive research, development, testing, and patents and the novel Neoloy polymeric alloy for

PRS-Neoweb geocells are evidence of PRS’ leadership in the field of geocells. These efforts included

collaborative research with world renowned geotechnical experts and researchers, such as Professors’

Jie Han, (U. of Kansas), Dov Leshchinsky, (U. of Delaware), Dr. K. Rajagopal, (IIT–Madras, Chennai,

India, Peter Ling, (Columbia U., NY), USA, Norbert Meyer (Clausthal U., Germany) and international

railway authority Dr. Allan Zarembski, and resulted in more than 40 professional papers published in

the last few years on PRS-Neoweb.

The collaborative testing and certification program also included leading institutes and transportation

authority’s around the world, such as the US Federal and state Departments Of Transportation (DOTs),

the Federal Railroad Administration (FRA), RZD Russian National Railways, KOAC-NPC Road Standards

Institute, Holland, Indian Roads Congress and additional standards, geosynthetics and transportation

agencies in the US, Poland, India, Israel, Colombia, Romania, Czech Republic, Mexico and South Africa.

Test Results

The use of PRS-Neoweb in the ballast/subgrade interface area has been shown to decrease the rate of

track surface geometry degradation (both surface and cross-level) under a range of traffic loadings.

Tests have confirmed this, with reductions in rate of degradation (corresponding to extension in

surfacing intervention cycles) ranging from factors of 1.67 to 10+.

Among the specific tests reported are:

Geotechnical tests on South African Railways (Spoornet) at the Amandebult Test Site with

reported improvement in performance due to use of Geocell material of a factor of 1.67. [1,2]

Laboratory testing of PRS-Neoweb reinforcement in the ballast layer performed at Columbia

University with reported improvement in performance due to use of PRS-Neoweb of a factor

of 2.0. [3]

Field testing at the Transportation test Center, Pueblo, CO on an artificially created “poor

track” zone of the FAST test track with reported improvement in performance due to use of

Geocell material of a factor of between 5 and 10.

In all cases, measurable improvement of the order of 1.67 or greater was recorded under the reported

testing conditions which included full

scale field testing under heavy axle

load traffic conditions.

Based on this analysis, it can be seen

that the PRS-Neoweb system has a

positive ROI (and thus a well defined

value) for track with very short

surfacing cycles ( one year or less) ,

which corresponds to track with poor

or weak subgrade conditions.

RO

I (%

)

200%

150%

100%

50%

0%

-50% 0

-100%

ROI of NeoWeb ( Type A)

2 4 6

NeoWeb Extension of Surfacing Cycle

8

surfacing cycle = 0.5 years surfacing cycle = 1.0 years surfacing cycle = 2.0 years

PRS-EN-TD-LS-2002 8/17 Rev. 13.01

This improved track geometry retention ability, translates into an extension in track geometry

maintenance cycles (intervention cycles, e.g. tamping cycles) and associated cost savings due to the

increased surfacing cycle (reduced number of tamping operations required over the time) and the

avoided train delay costs associated with the eliminated tamping cycles.

Research Results - PRS-Neoweb vs. HDPE Geocells

While the basic confinement principles of geocells were readily understood, the influencing factors of

the reinforcement were only investigated, tested and qualified with PRS sponsored research. The

research included plate loading box tests, full-scale moving wheel tests, and field demonstrations on

PRS’ Novel Polymeric Alloy (NPA), Neoloy-based PRS-Neoweb geocells, as well as HDPE geocells.

The research proved that not all geocells

are equal. The studies and tests have

demonstrated clear benefits of Neoloy-

based PRS-Neoweb reinforcement in terms

of increased stiffness and bearing capacity,

wider stress distribution, reduced

permanent deformation, and prolonged

roadway life.

Testing also showed that the performance

of geocell-reinforced bases depends on the

elastic modulus of the geocell. The geocell

with a higher elastic modulus had a higher

bearing capacity and stiffness of the

reinforced base. Geocells made from Neoloy were found significantly better in ultimate bearing capacity, stiffness, and reinforcement

relative to geocells made from HDPE (Pokharel, et al, 2009).

PRS-Neoweb geocells showed better creep resistance and better retention of stiffness and creep

resistance particularly at elevated temperatures, verified by plate load testing, numerical modeling

and full scale trafficking tests (Pokharel, et al 2011).The research also demonstrated that Neoloy-

based PRS-Neoweb has a lower thermal expansion coefficient and creep reduction factor, and higher

tensile stiffness and strength than HDPE geocells (Thakur, et al, 2010).

PRS-EN-TD-LS-2002 9/17 Rev. 13.01

NEOLOY-BASED PRS-NEOWEB SPECIFICATIONS

Evolving Standards for Geocells

Current standards evolved from the 2D geogrids and geotextiles. These do not reflect the behavior of

3D geocells in soil, nor do can they assess long-term performance such as: dynamic loading,

permanent plastic deformation, effect of temperatures, environmental durability, etc.

Therefore PRS decided to utilize methods commonly used by the pipe, automobile, electronic,

military, security and construction industries for testing, verification and quality assurance of polymer

plastics for its Neoloy-based PRS-Neoweb geocells. These methods are particularly suited for

predicting long-term behavior and accumulated plastic strain in a geosynthetic under loading under

different mechanical stresses, frequencies and temperatures. These methods include:

TMA – Thermo-Mechanical Analysis

DMA – Dynamic Mechanical Analysis

SIM – Stepped Isothermal Method

CTE – Coefficient of Thermal Expansion

DSC – Differential Scanning Calorimetry

At the same time new standards for geocells are being developed leading experts in geosynthetics in ASTM technical committee D-35, in which PRS is involved. The goal is to set new industry standards that more accurately reflect 3D geocell geometry and material performance in the field rather than lab tests of individual strips and virgin materials that are used by most manufacturers today.

Although the commonly used

ASTM/ISO standards utilized by many industries to evaluate polymer performance have not yet been adopted by geocell industry, PRS

has adopted to provide reliable and verifiable assessment of geocell properties and long-term

performance.

The following specifications are described in the following sections:

Dimensional Stability – Cell Ability to Withstand Thermal (Temperature) Cycling

SIM Accelerated Creep Test & Tensile Strength

Flexible Storage Modulus – Performance at Elevated Temperatures

Oxidation Resistance (OIT) – Long Term Reliability of Polymer

Photochemical (UV) Resistance (HPOIT)

PRS-EN-TD-LS-2002 10/17 Rev. 13.01

DIMENSIONAL STABILITY – Cell Ability to Withstand Thermal (Temperature) Cycling

Changes in temperature cause expansion and contraction of any material – In a polymeric geocell

heating expands the cell resulting in a loss of confinement,

while cooling contracts the cell, which can lead to failure

of the walls and seams.

Geocells must be able to retain their original dimensions

(“dimensional stability”) when subjected to varying

degrees of temperature, moisture, pressure, or other

stress. A geocell that loses its original dimensions impairs

confinement and compaction, leading to degradation or

failure of a pavement structure.

PRS-Neoweb has the highest dimensional stability of any

available geocell, as measured by the Coefficient of

Thermal Expansion (CTE), a standard industry test. A

lower number means the product is more resistant to

permanent deformation from thermal cycling.

The unique Neoloy alloy based on nano-fibers in a

polyolefin is chemically very stable. This gives PRS-

Neoweb the lowest CTE of any geocell available, 2.5-5x

lower than HDPE-based geocells.

DIMENSIONAL STABILITY

PROPERTIES DESCRIPTION UNITS TEST METHOD

Coefficient of Thermal Expansion

(CTE)

< 80 ppm/ °C ISO 11359-2 (TMA);

ASTM E831*

(*) CTE measurement range from -30°C to +30°C

CTE is measured by Thermo-Mechanical Analysis (TMA), a widely-used test method in the pipe,

automobile, electronic, and construction industries.

PRS-EN-TD-LS-2002 11/17 Rev. 13.01

SIM Accelerated Creep Test & Reduction Factor

The Stepped Isothermal Method (SIM) was developed to predict the accelerated creep of polymers for

a lifespan of 50-100 years (ASTM D6992). SIM measures the cumulative plastic distortion of the

polymer product by subjecting it to a constant load at different temperatures for a specified time. This

technique "accelerates" the creep by increasing the temperature in steps and then shifts the data

(using time-temperature superpositioning principles) to longer time periods. The SIM technique allows

for more than 10,000 hours of creep to be simulated in less than 24 hours. The SIM method also

enables calculation of the allowed strength for long term design.

In this test the End of Life for the product is not based on rupture of the cell wall or seam, but rather a

permanent plastic deformation exceeding 10%. Polyolefin (PE, PP) tends to fail unexpectedly at strains

above 10% caused by “crazing” in the polymer structure, leading to a loss of confinement and failure.

Note that the accelerated creep of Neoloy-based PRS-Neoweb sample is 9x lower than HDPE

sample.

SIM Accelerated Creep Test – Comparison of Neoloy vs. HDPE

35.3 325.5

Neoloy HDPE

PERMANENT DEFORMATION (CREEP) REDUCTION FACTOR

DESCRIPTION TEST METHOD Resistance to Permanent Deformation (Creep) Reduction Factor

5 years 10 years 25 years 50 years

< 1.2 <1.4 <1.9 <2.9

ASTM D-6992 (SIM) (5)

The In-isolation creep strain data can be used to estimate the post-construction strains and

permanent deformations (see Allen and Bathurst, 2002b) via data extrapolation in complex

mathematical models.

PRS-EN-TD-LS-2002 12/17 Rev. 13.01

FLEXIBLE STORAGE MODULUS – Performance at Elevated Temperatures Polymers tend to lose resistance to deformations (elastic modulus) at high temperatures. A geocell

system must be able to function under elevated temperature conditions and still deliver consistent

performance. This means that the geocell will maintain its shape and will not "creep" or expand under

the dynamic loading, thereby losing confinement or even worse crack and fail.

The flexible storage modulus is a metric of the geocell resistance to elevated temperatures. A cost

effective method to measure the elastic modulus at elevated temperatures is by utilizing Dynamical

Mechanical Analysis (DMA). DMA measures the accumulated plastic strain under loading under

different mechanical stresses, frequencies and temperatures together. The DMA data processing also

enables the determination of effective temperature service range,

Unlike HDPE which is sensitive to high temperatures, Neoloy-based PRS-Neoweb shows predictable

stiffness vs. temperature rise for accurate risk analysis and long-term design. Neoloy-based PRS-

Neoweb’s effective service range is -40°C to +60°C.

This method is well supported by ASTM and ISO standards, widely available and commonly used in the

automotive, electronic, military industries.

PERFORMANCE AT ELEVATED TEMPERATURES

PROPERTIES DESCRIPTION UNITS TEST METHOD

Flexural Storage Modulus at sample temp:

30°C

45°C

60°C

> 750

> 650

> 550

MPa

ISO 6721-1,

ASTM E2254

(DMA)

DMA enables an analysis of the effective

service temperature range using the

following:

storage modulus (elasticity)

loss modulus (plasticity)

loss tangent (an index for major change in mechanical properties, calculated as ratio between loss modulus and storage modulus);

The DMA analysis is performed in the range

plus 150°C to minus 150°C.

PRS-EN-TD-LS-2002 13/17 Rev. 13.01

OXIDATION RESISTANCE (OIT) – Long Term Reliability of Polymer

Providing long-term protection that is required by geocell polymers is a complicated process requiring

a high degree of technical competency – both in the selection of additives and their blending in the

manufacturing process. Heat stabilizers enable Neoloy based PRS-Neoweb geocells to survive

environmental conditions, such as heat and exposure to free radicals (ozone, ionizing radiation,

oxidative processes in soil, sewage and industrial waste) for many years.

Heat stabilizer content is measured by the Oxidative Induction Time (OIT) method. OIT is an accurate

indicator of the long-term reliability of the polymer protection to withstand prolonged exposure to

oxidation. This method is widely used for testing geosynthetics in critical applications, such as

geomembranes.

OXIDATION RESISTANCE

PROPERTIES DESCRIPTION UNITS TEST METHOD

Oxidative Induction Time (OIT)

(virgin material prior to any aging)

≥ 125 minutes ISO 11357-6, ASTM

D3895 (OIT @ 200°C)

This method is performed on a sample strip heated to 200°C in DSC (Differential Scanning Calorimetry)

under a protective atmosphere (nitrogen, argon) until melting. Then oxygen is pumped in at high

pressure. Under these conditions all the heat stabilizers react and the time until an Exothermic

reaction (oxidation) starts is measured. The more UV stabilizer there is in the product, the longer the

reaction time will be.

PHOTOCHEMICAL (UV) RESISTANCE (HPOIT)

Stabilizers that prevent polymer degradation from UV radiation belong to the Hindered Amine Light

Stabilizers (HALS) family of heat stabilizers; these are essential additives that allow Neoloy based PRS-

Neoweb geocells to survive environmental conditions that include heat and direct and diffused solar

radiation for many years. The heat stabilizer content is measured by the High Pressure - Oxidative

Induction Time (HPOIT) method (ASTM D5885).

PHOTOCHEMICAL RESISTANCE

PROPERTIES DESCRIPTION UNITS TEST METHOD

Durability to UV Degradation

(UV Resistance)

>500 minutes ASTM D5885

(HPOIT @200°C)

This method is performed the same as OIT on a sample strip heated to 200°C in DSC (Differential

Scanning Calorimetry). The more UV stabilizer in the product, the longer the reaction time will be. If

HPOIT is greater than 500, and Carbon black is 3% and more of type P, the protection is >50 years.

PRS-EN-TD-LS-2002 14/17 Rev. 13.01

APPENDIX – SUMMARY OF RESEARCH

PRS-Neoweb Railway Embankments – Maintaining Ballast Geometry (Leshchinsky, B., Ling, H., et al, Columbia U., USA)

Leshchinksy, B., (2011) “Enhancing Ballast Performance using Geocell Confinement,” Advances in Geotechnical Engineering, publication of Geo-Frontiers 2011 conference, Dallas, Texas, USA, March 13-16

Leshchinksy, B., Ling H., Leshchinksy, D., Liming L. (2010) “Summary of Reinforced Embankment Tests for PRS Mediterranean Ltd.”, Research Paper, Columbia University, January 5.

These papers describe research on loading tests of model rail embankments. The tests measured the

strength and deformation behavior of Neoloy based PRS-Neoweb in 6 different embankment

configurations. The results showed that PRS-Neoweb greatly restricted vertical deformation by 40-

72% and lateral displacement by 50-67% under loading. PRS-Neoweb was very effective in increasing

strength and preventing excessive deformation in the embankment. Vertical displacement under

cyclical loading was significantly reduced – little displacement occurred in the last 45,000 cycles,

indicating a stiffening and stabilization of the railway ballast.

PRS-Neoweb was stable under controlled cyclic loading within the stress amplitude of many

transportation applications (roadways, train, ballast, etc.). Measurements showed that the presence

of geocell allowed for a significant increase in stiffness and strength while reducing permanent

deformation implying that an optimized use of geocell reinforcement could lead to significant

reduction in maintenance due to ballast degradation.

Contribution to Pavement Reinforcement (Rajagopal, et al, Indian Institute of Technology, Madras, India and Kief, PRS)

Kief, O., and Rajagopal, K. (2011) “Modulus Improvement Factor for Geocell-Reinforced Bases.” Geosynthetics India 2011, Chennai, India, September 22-23

Kief, O. and Toan, T.D., (2011) “PRS-Neoweb 3D Cellular Confinement System for Structural Pavement Reinforcement of Roads & Railways.” Geotec Hanoi 2011, Vietnam, September 15.

Rajagopal, K., Veeraragavan, A., Chandramouli, S. (2011) Report on Plate Load Tests at Govind Dairy Factory, Phaltan and Interpretation - Modulus Improvement Factor, Technical Report, Indian Institute of Technology Madras, Chennai

Since NPA PRS-Neoweb geocells improve the moduli of pavement layers, it can be deployed in the

upper base layers of heavy-duty paved roads, as shown in the demonstration project. In addition to

defining the reinforcement mechanisms and influencing factors, recent research has also calibrated

and integrated the use of NPA geocells in road design methodologies.

In particular, the modulus improvement factor (MIF), verified in multiple research projects and field

demos provides a reliable method for quantifying the NPA geocell contribution to the pavement

structure for use in the design of unpaved and paved roads and railways. The MIF value obtained from

the field test, laboratory test and finite element studies is 2.75. This confirms similar results in other

research, dependent upon the material of infill, subgrade and location of reinforced layer.

PRS-EN-TD-LS-2002 15/17 Rev. 13.01

Geogrid Trial Road Base (Van Gurp, Westeral, KOAC-NPC Institute, Holland)

Van Gurp, C.A.P.M., Westera, G.E. (2008) “Geogrid Trial Road Base NL 2008”, KOAC-NPC, Netherlands, Final Report.

The leading road research and standards institute in Holland conducted controlled field trials for

geosynthetics reinforcement of road bases. Test data was based on deformation and stiffness trials of

full-scale structures in controlled sites (enclosed hangars). PRS-Neoweb was the only geocell

manufacturer among 7 leading geogrid manufacturers. In addition, PRS-Neoweb was also the only

geosynthetic reinforcement tested that could accommodate inferior aggregate material as the road

base infill. The results showed that PRS-Neoweb had the highest Road Base Thickness Reduction

Factor of any tested product (up to 72% average unlimited), and substantially exceeded the known

values for geogrids.

PRS-Neoweb Base Reinforcement Research and Full Scale Trafficking Testing - (Han J. et al, University of Kansas, USA)

The following is a sample of comprehensive studies, moving wheel tests, static and dynamic loading

tests and field trials conducted at the University of Kansas, under Professor Dr. Jie Han over the last

five years. These studies demonstrated how Neoloy-based PRS-Neoweb increases stiffness and

bearing capacity, distributes stress wider, reduces permanent deformation, and prolongs roadway life

compared to unreinforced and HDPE-geocell road bases.

Onsite Use of Recycled Asphalt Pavement and Geocells to Reconstruct Pavements, Mid-America Transportation Center Report-462. Han, et al (2012). On-site use of recycled asphalt pavement materials has obvious benefits from economic, to environmental, to sustainability points of view. This research demonstrated the benefit of using recycled asphalt pavement (RAP) materials in PRS-Neoweb geocell-reinforced base courses with a thin new overlay.

Tough Cells – Neoloy-based PRS-Neoweb for Sustainable Roadway Applications, Roads and Bridges, Han, et al (2011). Synopsis of comprehensive research at the University of Kansas, confirming the performance of Neoloy-based PRS-Neoweb as compared to unreinforced and HDPE- geocell road bases. A key conclusion was that the benefit of geocell reinforcement increased with an increase of the modulus (tensile stiffness) of the geocell. The research included modeling and calibration of a design methodology for roads employing PRS-Neoweb reinforced bases.

Accelerated Pavement Testing of Unpaved Roads with Geocell-Reinforced Sand Bases, Transportation Research Board, Florida, Yang, et al (2011). Full-scale moving wheel test results demonstrated that Neoloy-based PRS-Neoweb improved the stability of unpaved roads and reduced the permanent deformation – with sand infill performing at the same level as high-quality A1 aggregate.

PRS-EN-TD-LS-2002 16/17 Rev. 13.01

Effect of Infill Material on the Performance of PRS-Neoweb-reinforced Bases, 9th International Geosynthetics Congress, Brazil, Han, et al, (2010). Plate load tests demonstrated how Neoloy-based PRS-Neoweb reinforcement significantly improved the performance of inferior quality infill materials, such as sand and quarry waste, compared to unreinforced bases.

Load Bearing Tests on Bearing Capacity of PRS-Neoweb-Reinforced Bases, Conference on Bearing Capacity of Roads, Railways and Airfields, Illinois, Pokharel, et al (2009). Static and dynamic plate testing of PRS-Neoweb showed an increase in bearing capacity, stiffness and elastic deformation with reduced permanent deformation.

Experimental Study of Reinforcement of PRS-Neoweb vs. HDPE-based Geocell, Transportation Research Board, Pokharel, et al (2009). Plate tests evaluated the influence factors on a single geocell on sand – geometry and material. Neoloy-based PRS-Neoweb increased bearing capacity and stiffness and reduced settlement of the compacted sand base course significantly more than geocells fabricated from HDPE.

Accelerated Pavement Testing of Geocell-Reinforced Unpaved Roads over Weak Subgrade, Transportation Research Board, Florida, Pokharel (2011). Full-scale trafficking tests were conducted at the Accelerated Pavement Testing facility demonstrated that Neoloy-based PRS-Neoweb improved the performance of unpaved roads in terms of rut depth and angle of stress distribution.

Behavior of Geocell-Reinforced Granular Bases under Static and Repeated Loads, IFCEE, Florida, Pokharel, et al (2009). The study of reinforced bases under static and repeated loads on a loading plate showed that the single geocell could increase the stiffness by approximately 50% and the maximum load by 100% as compared with those of the unreinforced base.

Bearing Capacity Improvement in Road Constructions (Meyer, N., et al, Clausthal University, Germany)

Emersleben A., Meyer M. (2010). Verification of Load Transfer Mechanism of Geocell Reinforced Soil in Large Scale Model Tests and In-Situ Test Fields. GeoFlorida 2010: Advances in Analysis, Modeling and Design, Geotechnical Special Publications No. 199, Vol 2/4.

Emersleben A., Meyer M. (2009). Interaction Between Hoop Stresses and Passive Earth Resistance in Single and Multiple Geocell Structures, GIGSA GeoAfrica 2009 Conference, Cape Town, South Africa, September 2-5.

Emersleben, A. and Meyer, N. (2008). “Bearing Capacity Improvement of Gravel Base Layers in Road Constructions using Geocells,” International Association for Computer Methods and Advances in Geomechanics (IACMAG), Goa, India.

These published studies have thoroughly evaluated the use of PRS-Neoweb geocells for reinforcement

of flexible structural pavements. Extensive testing was carried out in the laboratory with plate loading

of geocells in large scale test boxes, in addition to a number of large field installations in actual

roadway constructions were carried with pressure cell instrumentation and monitoring.

The studies evaluated how the geocell reinforcement mechanisms work, and describe the improved

geotechnical engineering forces provided by the soil-cell composite structure. Results from

comparative field tests – including full- scale field testing based cyclical dynamic loadings – validated

the results achieved in laboratory plate box test testing.

PRS-EN-TD-LS-2002 17/17 Rev. 13.01

PRS-Neoweb increased the load bearing capacity of the soil by a factor of 5, reduced differential

settlement by up to 80% and decreased vertical stresses in the soft subgrade by more than 40%.

Additional plate loading test box studies demonstrated that geocells increase the bearing capacity of

the soil and reduce the vertical stress on subgrades by 30-45%. The performance of a 40 cm PRS-

Neoweb reinforced base layer equaled a 70 cm unreinforced high quality aggregate layer.

Earth Retention – Seismic Research (Leshchinsky, D., et al, University of Delaware, USA)

Leshchinsky, D. (2009) “Research and Innovation: Seismic Performance of Various Geocell Earth- retention Systems,” Geosysnthetics, No. 27, No. 4, 46-52.

Leshchinsky, D., Ling, H.I., Wang, J-P., Rosen, A., Mohri, Y. (2009) “Equivalent Seismic Coefficient in Geocell Retention Systems,” Geotextiles and Geomembranes Journal, No. 27, 9-18.

Ling, H.I., Leshchinsky, D., Wang, J.P., Mohri, Y. and Rosen, A. (2009) “Seismic Response of Geocell Retaining Walls: Experimental Studies”, Journal of Geotechnical and Geoenvironmental Engineering, 135, No. 4, 516-524

The following three papers authored by Dr. Leshchinsky (et al) reviewed testing of PRS-Neoweb earth

retention walls at the shake table National Seismic Research Institute in Japan. The tests on a variety

of wall types replicated seismic activity similar to a severe earthquake. The study concluded that

geocells can be used successfully to form gravity walls as well as reinforcement layers even when

subjected to a very high seismic load beyond that of the Kobe earthquake.

The study resulted in recommended seismic reduction factors (0.3-0.4) that are used in the design of

gravity and reinforced walls. Dr. Leshchinsky noted, however, that geocells made from HDPE are

unsuitable for long-term applications, and guidelines were given to PRS to further the development of

its Neoloy based PRS-Neoweb geocell for demanding applications requiring long-term performance.

Field Demonstration of PRS-Neoweb in Amtrak Track Substructure for High Speed Passenger Rail Operations

Zarambski, A. (2011) Field Demonstration of Geocell Track Substructure Support System under High Speed Passenger Railroad Operations. Proposal to US Department of Transportation

A full scale in-track field evaluation of PRS-Neoweb cellular confinement system is to be performed in

2013 under actual main line conditions on Amtrak track on the heavily trafficked Northeast corridor.

The field trial for the US DOT (Department of Transportation) - Federal Railroad Administration (FRA) is

a collaborative effort of the Amtrak National Railroad Corporation, Zeta-Tech (Harsco Rail) railway

consultants, researchers from Colombia University, and experts from PRS.

PRS-Neoweb will be used to reinforce a problematic section of track, which suffers significant mud

pumping and track geometry degradation from poor subgrade. Monitoring over a 12-18 month period

will record stress reduction and settlement reduction due to PRS-Neoweb mattress acting as a flexible

beam, as well as measurements of track quality by Amtrak’s track geometry vehicles. The purpose of

the test is to demonstrate the effectiveness of Neoloy-based PRS-Neoweb reinforcement in reducing

degradation and validate lab testing showing a reduction in the surfacing (maintenance) cycle on the

order of double or even more. The final report describing all of the activities, analyses and results of

the project will include track geometry (TQI) monitoring and life cycle cost analysis.