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Geosynthetics Soil reinforcement
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TENAX solutions for railways
Vinkovci/Tovarnik, Croatia
Geogrid reinforcement of railway ballast.
185,000m2 of geogrid have been
installed for Croatian Railroad.
The repeated rapid passage of trains in very brief intervals of time,
apply dynamic loads to the soil
resulting in very intense compression
and decompression cycles. Thus railway
foundations are being subject to constant
fatigue stress leading to frequent and
expensive maintenance requirements.
Although these maintenance costs are
high, by far the most expensive cost factor
is the reduction in revenue caused by the
disrupted services.
TENAX geogrids are extremely effective
in reinforcing unbound granular layers in
roads and other trafficked areas such as,
car parks, airports and docks. The use of
geogrids in ground stabilisation allows the
overall construction depth to be reduced.
This saving on materials and excavation also
provides safe working platforms that meet
economic and environmental constraints.
By incorporating TENAX RailGrid
(LBO 370) within railway construction
layers, it is possible to combine major cost
savings with considerable performance
benefits at both the ballast and sub-ballast
levels.
When ballast or sub-ballast granular material
is compacted over TENAX geogrids, stone
particles partially enter the apertures of the
grid and are eventually "locked-in" to create a
strong and positive interlock along the plane
of the geogrid.
This locking mechanism
enables the grid to resist horizontal
movement of the stones which improves
ballast performance and reduces railway
ballast settlement.
Reinforcing solution for existing railways
Over time the constant movement of traffic
over the track causes the railway ballast to
eventually deteriorate with voids forming
within the ballast structure. Often, from the
track side, sleepers can be clearly seen
bouncing up and down as the wheels pass
over them.
This excessive movement is dangerous
and so the voids need to be filled and
re-compacted to give a firm base for each
sleeper. In other areas, loose broken
fragments fill the voids within the ballast
matrix reducing the drainage characteristics
of the railway construction layers.
Ballast tamping operations are then
carried out to maintain track line and levels.
Tamping machines are designed to vibrate
the ballast and force it under the sleeper.
These combined actions cause the ballast
to form a close matrix which can support the
track effectively once again.
However, continuous tamping operations
can cause further particle breakage and
eventually the ballast is spent and has to be
replaced.
It is therefore desirable to increase the
ballast life so that tamping requirements
are reduced resulting in less maintenance
activity, less disruption to operations and
increased savings for the rail operator.
TENAX RailGrid LBO 370 geogrids are
used to limit the deformation in ballast layers
by providing interlock along the plane of the
geogrid.
This reduces the formation of voids and
therefore prolongs the life of the ballast
thereby passing on significant cost benefits
to the rail operator.
New line construction
TENAX geogrids are also used in new line
construction over poor subgrade. Their use
within the sub-ballast allows substantial
reductions in the required layer thickness
due to the reinforcing effect. This can in
addition often allow the depth of excavation
of poor formation soils to be reduced
with less disposal costs. Furthermore,
the geogrids can be used with recycled
aggregate such as crushed concrete.
The economic and environmental benefits
of using Tenax in the sub-ballast have been
widely experienced over recent years,
particularly in the construction of new rail
corridors across mainland Europe.
Ballast reinforcement
Geogrid improves stiffness of ballast
and provides lateral confinement of
coarse aggregate.
Sub-ballast reinforcement
Geogrid limits deformation of overlying
ballast layer and distributes stresses
along the plane of the geogrid.
Midgham, England
Midgham, England
TENAX RailGrid installed to increase
ballastperformance and reduce
maintenance frequencies.
| TENAX RailGrid LBO 370 Resistance to abrasion according to EN ISO 13427 |
Retained strength (%) |
Retained extension (%) |
||||
| Control | Exposed | |||||
| Tensile strength (N) |
Extension at Maximum Load (%) |
Tensile strength (N) |
Extension at Maximum Load (%) |
|||
| MD | 2302,2 | 13,3 | 2280,8 | 12,7 | 99,07 | 95,63 |
| TD | 2664,0 | 12,9 | 2521,0 | 12,1 | 94,63 | 93,64 |
| MD: machine direction TD: transversal direction |
||||||
The benefits
Key benefits when using TENAX RailGrid geogrids within railway foundation layers:
Improved ballast performance allowing for consistent high speeds to be achieved.Improved stabilisation of track foundation layers.Reduction in the rate of ballast degradation and settlement.Reduction in overall maintenance cycles.Reduction in tamping operations, thereby increasing the life of the ballast.Reduced excavation and use of expensive imported fill.
TENAX RailGrid geogrids are
manufactured from a unique process
of extrusion and then bi-oriented to
enhance their tensile properties.
They are
manufactured from polypropylene and
produced with high tensile stiffness in
both longitudinal and transverse directions
allowing load to be resisted at very low
strains.
They are designed specifically
with large rigid square apertures having
an optimum mesh size of 65 mm therefore
maximising mechanical interlock with the
railway ballast.
Bi-oriented geogrids provide an effective
way of reducing the rate of ballast
settlement over soft subgrades.
Independent trials have confirmed that it
is the stiffness and the size of the geogrid
apertures that determine the structural
performance of pavements.
TENAX geogrids provide an extremely
cost-effective solution for the reinforcement
of ballast over soft subgrade bringing
signifi cant benefi ts to the railway engineer.
It is well known that railway ballast is one of the most aggressive granular materials for geosynthetic rail applications, composing of large sized, angular stones. It is therefore important to confi rm the performance of the geogrid after installation by determining the effective reduction in tensile properties due to this possible damaging action. A very simple index test, “Abrasion Damage Simulation” (EN ISO 13427) can be used to give an indication of these abrasion effects. Tests performed on TENAX RailGrid at independent laboratories have shown residual strengths in excess of 90% in both directions, thus clearly demonstrating the suitability of the geogrid for reinforcement of the railway ballast.
Certification and approvals
TENAX RailGrid LBO 370 is certified by European railway authorities such as Network Rail, UK’s national railway authority, and Delta Rail, The Netherlands’ national railway authority.
 PA05/03529 0057/100852 |
 |
England
Extensive research continues on a
live site involving instrumentation
of the TENAX geogrids.
Separation and filtration function
With TENAX GT Tenax bi-oriented geogrids are also available as a composite material where a geotextile is bonded to the geogrid.
In addition to the reinforcement function provided by the geogrid, the geotextile component offers additional separation and filtration functions where necessary.
Mantgum, The Netherlands
Friesland track ballast renewal was
completed using a ballast-cleaning train
running at 3 m/s simultaneously placing
a geocomposite to stabilise the ballast/
subgrade interface and to minimise the
upward movement of subgrade fines.
Drainage of railway tracks is essential to ensure acceptable track performance. The cost of maintenance or, conversely, the deterioration of track components is directly impacted by the condition of the drainage system.
Excess water can create a saturated state in the ballast and sub-ballast, causing premature failure of the ballast system leading to frequent repair operations and significant increases in track maintenance costs.
Achieving proper drainage is not simply a matter of excavating a cross trench and letting water out of the track but it is reliant on providing a free draining base.
The use of TENAX TENDRAIN geocomposites over traditional methods of drainage can provide a rapid and cost effective solution for the requirements of sub-surface drainage in railway tracks. Instead of the installation of expensive granular layers to facilitate drainage, TENAX TENDRAIN geocomposites can be used to collect water filtering down through the railway construction layers as well as capturing water seeping upwards from the subgrade as a capillary break.
TENAX TENDRAIN can be installed
between the foundation soils and the
upper layers of inert material providing
a stiff separating function capable of
supporting high compressive loads
whilst preventing any accumulation of
water thus achieving a well-drained and
dry base with a longer design life,
higher mechanical properties and
with no water inclusion.
The benefits
Benefits of installing TENAX TENDRAIN include:
A major cost saving when compared with traditional filtration methods e.g. imported granular filtration blankets.
An improved stiffening and overall strength of ballast and sub-ballast layers due to better control of the water.
A reduced potential for hydraulic pumping of fine soils from subgrade up into the sub-ballast and ballast.
A reduced potential of excess pore water pressure build-up under cyclic loading.
A reduction in ballast degradation from slurry abrasion, chemical action and freezing of water.
Research and testing
A critical measure for the operational life of a drainage geocomposite is the reduction in thickness when compressive stresses are applied to its surface as this thickness reduction ultimately affects the drainage capacity of the product.
After initial elastic deformation occurs, the deformation related to creep phenomena is measured through compressive creep testing to EN 1897 standard.
When tested in accordance with EN1897, the chart shows the drainage core of TENAX TENDRAIN geocomposites as having a curve that is almost flat after 10,000 hours. This means that the residual thickness after this period tends to be constant, and that no further deformations will occur, showing the product is able to maintain its hydraulic capacity in the long term under high compressive stresses.
Padova-Mestre, Italy
Capillary break layer under the new
high speed train line Milan-Venice
in the Venice-Mestre area.