1. Balfour Beatty Rail Limited
XiTRACK Polyurethane Ballast Reinforcement – Case Studies
Reference: BBR-2015/1515
Version 15
April 2015
2. Balfour Beatty Rail Limited a company registered in England under company no. 1982627 with its registered office at 130 Wilton
Road, London, SW1V 1LQ, an agent of Balfour Beatty Group Limited registered in England and Wales, with company registered no.
101073, registered office Fourth Floor, 130 Wilton Road, London, SW1V 1LQ.
Page ii
Contents
1 Introduction..........................................................................................................................1
1.1 Lateral Restraint ...........................................................................................................2
1.2 Vertical Alignment.........................................................................................................2
1.3 Minimise Ballast Settlement..........................................................................................2
2 Applications .........................................................................................................................3
2.1 Business Case for XiTRACK installations .....................................................................3
3 Installations..........................................................................................................................4
3.1 Toadmoor Tunnel .........................................................................................................4
3.2 Canal Tunnels ..............................................................................................................4
3.3 Whiley Hill Masonry Arch Bridge XiSPAN Trial .............................................................5
3.4 University Station, MTR, Hong Kong.............................................................................6
3.5 Famagosta-Assago, Milan Metro, Italy..........................................................................6
3.6 Dalston West Curve transition, East London Line .........................................................6
3.7 Dalston West Curve Sewer, East London Line .............................................................7
3.8 Gravel Hole, West Coast Main Line (Up Line)...............................................................7
3.9 River Lea Under-bridge, North London Line..................................................................8
3.10 East London Line Extension .........................................................................................8
3.11 Kavanaghs Road Bridge Transitions, Brentwood..........................................................9
3.12 Clapham Junction, Windsor Ladder ..............................................................................9
3.13 Bletchley Fixed Diamond ..............................................................................................9
3.14 Newham Bog .............................................................................................................. 10
3.15 Peterborough Bridge 184............................................................................................ 10
3.16 Lock Lane Long Eaton, Bridge 3................................................................................. 10
3.17 Kentish Town PACT (Paved Concrete Track) System Transitions .............................. 11
3.18 Manningtree North Junction........................................................................................ 11
3.19 Grove Hill Tunnel, Tunbridge Wells............................................................................. 11
3.20 Syston North Junction................................................................................................. 12
3.21 Knighton Junction ....................................................................................................... 12
3.22 Keadby Bridge Abutment Reconstruction.................................................................... 12
3.23 Balavil Burn and Gynack Burn .................................................................................... 13
3.24 Falkirk Tunnel PACT System Transitions.................................................................... 13
3.25 Tottenham South Junction .......................................................................................... 13
3.26 Purfleet Deep Wharf Level Crossing........................................................................... 14
3.27 Bletchley..................................................................................................................... 14
3.28 Worplesdon Hop Garden ............................................................................................ 14
3.29 Norwich – Ely.............................................................................................................. 15
3.30 WCML Bridge Resonance Programme....................................................................... 15
3. Page 1
Introduction1
XiTRACK is a visco-elastic polymer which when poured onto ballast forms an in-situ polymer and
ballast geocomposite. The polymer cures as it penetrates up to a specified depth into the ballast to
form a 3-dimensional matrix or ‘reinforcing cage’.
The polymer is applied in-situ by mixing two chemical components through a mixing lance. The
polymer is poured on to and penetrates into the track ballast. The polymer typically cures within 10
to 15 seconds. It achieves 50% of its designed strength within minutes and reaches 90% of its
strength within 1 hour. The polymer satisfies the requirements of the UK Environment Agency.
Polymers of this type can typically develop strains in excess of 100% before failure in tension. The
benefit of using the polymer as a reinforcing element, is the ability to design the polymers rheology,
strength, stiffness, damping properties and cure rates. The ductility and damping properties of the
polymer make it an ideal material for railway environments where operating conditions can result in
sudden high dynamic loads (e.g. IRJs, wheel flats and discontinuities). Breakdown of the polymer,
is unlikely, however if breakdown occurs it leads to a conventional ballasted ‘state’ and drainage is
still maintained.
Bonding of the polymer to the ballast will occur but this is not critical, as the primary function of the
treatment is to generate polymer-reinforcing elements at every level in the ballast matrix, both
vertically and horizontally, essentially encapsulating the ballast. Bonding of the polymer, to the
ballast, is not therefore required for the technique to work, which is the fundamental difference with
ballast gluing where the system’s inherent strength comes from the cohesive bond.
The primary objective of utilising this technology is to maintain track geometry within designed
tolerances and reduce maintenance intervention. The design philosophy considers three separate
components, lateral and vertical restraint and ballast settlement.
Compressive Strength of Ballast Tensile Strength of Polymer Inherent Geocomposite Strength
4. Page 2
1.1 Lateral Restraint
The XiTRACK system as a solution to maintain lateral alignment is well proven. It has had multiple
applications in similar scenarios to provide restraint on curves, at platforms and through switch and
crossing units.
1.2 Vertical Alignment
The XiTRACK treated ballast will prevent ballast dilation and hence deterioration (loss of top,
maintenance input increase) where interfaces exist such as a structure to ballasted track. It is the
intention in this application to provide track restraint and manage track bed stiffness.
1.3 Minimise Ballast Settlement
Settlement in ballast is well documented. The XiTRACK treated ballast will not consolidate under
traffic, unlike ballast which is left untreated. Any loss of top or development of twist faults or risk of
differential settlement of the superstructure is therefore minimised. In principle the XiTRACK
treated ballast will act as a ground slab reducing the stress concentrations.
The system has several key benefits:
• Very Quick Setting. Replacement of any ballast on top of the XiTRACK layer can occur
immediately after application of the polymer as it sets in seconds. Under normal conditions
XiTRACK can be loaded by site traffic, including vibro-plates, 15 minutes after polymer
application and by rolling stock 30 minutes after polymer application.
• Long Service Life. The long life characteristics of polyurethanes are well documented. The
design is prepared such that the material operates within its yield strength.
• Free Draining. Approximately 30% of the void structure will be occupied by the XiTRACK
polyurethane in treated ballast, leaving the remainder open for drainage.
• Scheme Cost Benefits. XiTRACK is a value engineered solution that will produce life cycle
cost benefits. Savings are possible through much reduced compensation payments to Train
Operating Companies and Freight Operating Companies as a direct result of its very rapid
installation and curing time leading to smaller blockades and disruptive possessions. In addition
as it is an engineered ‘solution’ to recurring defects it will help reduce spend on future
maintenance.
• Can be applied at any time of the year.
• Is designed for the particular project and user requirements.
5. Page 3
Applications2
XiTRACK has a range of designed applications:
• Transitions to and from ballasted track to other track-forms such as slab track and bridge
structures.
• Increasing vertical stiffness of track to reduce or eliminate maintenance problems, or allow an
increase in line speed.
• Removal of “ballast memory” locations
• Protection to structures from impact loads
• Providing a designed resistance to buckling
• Providing a designed resistance to lateral toe loads at Switches and Crossings
• Achieving high fixity for clearances or platform stepping distances
• Washout and flood damage mitigation
2.1 Business Case for XiTRACK installations
There are broadly two sets of criteria which can be used to make a judgement on the
attractiveness of the XiTRACK solution; these are:
• Financial Analysis of the known facts and figures for the asset. This leads to an objective view
of returns, which can be measured against risks to develop a go/no go recommendation.
• Subjective Analysis of the benefits less easy to quantify and the “gut feel” of engineering
management.
Where XiTRACK has been installed the following benefits have been realised:
• Reduced or eliminated infrastructure maintenance
• General acceptance that good infrastructure reduces wear and tear on rolling stock
• Improved long-term track quality
• Improved ride quality
These benefits lead directly to reliability and safety improvements. Quantifying these benefits can
be more difficult than the former but they are generally agreed to exist.
The following examples illustrate how business cases for the installation of XiTRACK have been
arrived at across the full range of job types. The projects described in this paper have all been
subjected to a business case development by the client
6. Page 4
Installations3
3.1 Toadmoor Tunnel
As part of the Midland Mainline Line Speed
improvement Project the line speed through
Toadmoor Tunnel was increased from 60 to
80mph. Toadmoor has historically been a
difficult site to maintain and it was feared a
speed increase would make it more so.
XiTRACK was used to create a low
maintenance high fixity track form was installed
in the tunnel. The installation was undertaken in
non-disruptive possessions.
3.2 Canal Tunnels
The XiTRACK design was required to provide
stabilisation to cater for anticipated ground
movement at the Canal Tunnels Sonneville
slabtrack to ballast interface. Whilst also
providing lateral fixity to maintain track
alignment at this critical area.
The complex track geometry and location next
to the concrete slabtrack transition made it
particularly desirable to mitigate track
maintenance input as far as practicable.
7. Page 5
3.3 Whiley Hill Masonry Arch Bridge XiSPAN Trial
Network Rail owns and maintains the oldest masonry arch railway bridges in the world. Many are
beyond their design life and are suffering the effects of aging which is increasing the ongoing
maintenance burden.
Balfour Beatty Rail and a team of industry
experts worked with Network Rail to develop an
innovative, cost effective strengthening solution
to prolong the life of these critical assets and
preserve their historical legacy.
Balfour Beatty Rail worked with Network Rail to
identify a suitable structure to trial a polymer
based solution on. The bridge in question is at
Whiley Hill on the Stockton and Darlington line.
Built by George Stephenson in 1824, it is
possibly the oldest structure on the network.
To prolong the life of the structure the team needed to:
• Maintain or increase the capacity of the arch
• Stabilise or reduce the span deflection ratio
• Reduce or eliminate the causes of deterioration
To do this they needed to develop a solution that would:
• Be invisible to the track maintainer
• Have no visible or aesthetic effect on the bridge’s appearance
• Not alter the structural load paths or bridge failure modes
• Be capable of being implemented in short timescales with little or no disruption to traffic
Preliminary analysis and design work indicated that the creation of a geocomposite raft comprising
of ballast and advanced polyurethane, positioned between the track and bridge would address
these objectives.
8. Page 6
3.4 University Station, MTR, Hong Kong
XiTRACK was successfully installed between
the sleeper end and the platform wall to provide
lateral resistance to track movement.
In-situ testing on a test installation at Fo Tan
depot showed displacements of 0.9mm for
100kN sleeper end load.
This installation was completed June 2012.
Monitoring to May 2014, has showed a
maximum sleeper displacement of 3mm at
University station.
3.5 Famagosta-Assago, Milan Metro,
Italy
A new extension to the Milan Metro incorporated
a concrete slab track underbridge abutting
conventional ballasted track. XiTRACK was
used to combat voiding at the interface. The
installation took the form of a ladder structure
with edge beams, locking the ballasted track in
position and controlling track settlement,
resulting in a reduced potential for voiding at the
site. The XiTRACK installation was completed in
November 2010.
3.6 Dalston West Curve transition, East London Line
XiTRACK ballast reinforcement was used to
reduce the occurrence of voiding at the
interface between concrete slab track and
ballasted track. The treated section comprised
a ‘ladder type’ XiTRACK structure adjacent to
the slab track to reduce voids and dynamic
deflection of the ballasted track. Edge beams
were also installed to give increased lateral
resistance to the ballasted track to ensure
horizontal alignment of the ballasted track with
the slab track. These were installed over a
longer length than the ladder structure,
extending the reinforcement to a vehicle track
crossing. The XiTRACK installation was
carried out in order to help reduce future track maintenance requirements by reinforcing and
strengthening the ballast and giving transitional track stiffness characteristics. Work was
completed in August 2010.
9. Page 7
3.7 Dalston West Curve Sewer, East London Line
A Victorian cast iron sewer runs under the East
London Line at a very shallow depth beneath
the track. XiTRACK was used here in April
2010 to transition the track formation over the
sewer. The XiTRACK design protects the
sewer and prevents the creation of track
maintenance problems.
3.8 Gravel Hole, West Coast Main Line (Up Line)
A section of the West Coast Main Line in Lancashire
runs over an area of very poor ground which had lead
to the long-term imposition of a temporary speed
restriction. The soft ground lead to critical track velocity
and Rayleigh wave induced track maintenance
problems
XiTRACK formation improvement works were
undertaken in March 2010 with sub-ballast
reinforcement provided by the XiTRACK system.
Before and after Falling Weight Deflectometer
measurements were taken in order to assess whether
to reopen the line at 125mph line speed.
Measurements confirmed that the XiTRACK treated
track was working as designed and the line speed was
lifted to 125mph.
10. Page 8
3.9 River Lea Under-bridge, North London Line
This site was historically a maintenance problem due to a
sudden track stiffness change between this bridge and the
adjacent embankment. XiTRACK was used to create a
constant rate of change of stiffness between the bridge
and the embankment.
The work took place over Christmas 2009, and involved
application of XiTRACK in gradually higher concentrations
approaching the bridge over a predetermined distance.
This graded the stiffness of the track to match the bridge
by providing a varying degree of vertical reinforcement.
The scheme left a layer of ballast between the bottom of
the sleepers and top of the XiTRACK treated ballast in
order to allow the normal tamping regime to continue.
3.10 East London Line Extension
Extensive XiTRACK work was undertaken on the East London Line in August 2009. The work
included vertical track reinforcement on the Surrey Canal Road Line and on the New Cross Flyover
and increasing track fixity through stations.
The Surrey Canal Road Bridge had presented the project with a problem as switches and
crossings were to be positioned spanning the interface between a bridge and an embankment. It
was therefore necessary to have a solution that protected the switches and crossing from thermal
movement of the bridge and varying track support stiffness. These objectives were achieved by
creating a XiTRACK raft of reinforced ballast under the switches and crossings.
The XiTRACK technique was also used successfully to reinforce and stabilise the ballast between
the sleeper end and the platform wall at stations on the East London Line, increasing the track
fixity at these locations.
11. Page 9
3.11 Kavanaghs Road Bridge Transitions, Brentwood
In order to help prevent voiding at the interface
between a longitudinal timber bridge and plain-line
track, XiTRACK ballast reinforcement was used in
a ‘ladder type’ structure near the bridge/ballast
interface. The purpose of this treatment was to
reduce voids close to the bridge through 3-
dimensional ballast reinforcement and to provide a
graduated ballast stiffness (within the
geocomposite) to help reduce track deflection from
the ballast dynamic response.
The XiTRACK installation was carried out in order
to help reduce future track maintenance
requirements by reinforcing and strengthening the
ballast and giving transitional track stiffness
characteristics. Work was completed in July 2009.
3.12 Clapham Junction, Windsor Ladder
Clapham junction is one of the busiest railway
junctions in the world. Because of this, access for
inspection, maintenance and repair is very limited.
XiTRACK was chosen at this location to increase
the Reliability, Availability, Maintainability
(“RAMS”) requirements of the Windsor Ladder.
3.13 Bletchley Fixed Diamond
Following on from the continuous satisfactory
performance of XiTRACK that was installed at
some Switches and Crossings several years
earlier, the Track Maintenance Engineer utilised
XiTRACK to address voiding problems beneath a
fixed diamond that had lead to a speed restriction
and increased maintenance intervention. A pad
was constructed to give uniform stiffness to a layer
of ballast beneath the bottom ballast enabling
tamping activities to be unaffected.
The work was carried out in time for the temporary
speed restriction in place to be removed, ready for
an increased service frequency.
12. Page 10
3.14 Newham Bog
Here the East Coast Main Line rail route north of
Newcastle runs across a section of very poor
ground. A long history of problems had been
encountered at the interface with a boulder clay
formation and a line speed reduction was
necessary owing to the low Critical Track
Velocity at the site. XiTRACK Polyurethane
Ballast Reinforcement was used to stiffen up the
formation to provide a graded change from the
boulder clay to the soft peat bog, replacing
geocells which were installed in the 1980’s.
3.15 Peterborough Bridge 184
XiTRACK was specified as part of the plain line
track renewal works as a means of managing
track stiffness at the interface with a longitudinal
timber bridge. XiTRACK was applied to the
bottom ballast with the track in-situ as a means
of preventing future track quality problems and
voiding.
3.16 Lock Lane Long Eaton, Bridge 3
This was a maintenance scheme to prevent the
return of ongoing track quality issues at this
location. Along with the renewal of the
longitudinal timbers on the bridge, XiTRACK was
applied on the approaches and run offs with the
existing track in-situ to prevent track voiding at
the interface with the structure.
13. Page 11
3.17 Kentish Town PACT (Paved Concrete Track) System Transitions
At this location the existing concrete transition
structures between the slab and ballasted track
were beginning to fail and proving to be a
maintenance problem. They were replaced
with a XiTRACK design that enabled ordinary
track components to be used right up to the
interface with the slab thus considerably
reducing the maintenance burden.
A design, project management and installation
scheme was carried out successfully during the
associated plain line track renewal.
3.18 Manningtree North Junction
Here the change in track stiffness from a
structure to an embankment and then to an
under bridge was causing track quality
problems, particularly at the interface with
Switches and Crossings at the junction. During
the junction’s renewal the opportunity was
taken to install a layer of XiTRACK sub ballast
with a varying stiffness, designed to grade out
the hard spots caused by the structures.
3.19 Grove Hill Tunnel, Tunbridge Wells
This major construction scheme saw the
replacement of approximately 120m of failed
slab track system which had originally been
installed to maintain tight clearances through
the tunnel but had failed owing to drainage
issues. A bed of free draining XiTRACK treated
ballast was used instead with a collector drain
running along the centre. The track was laid on
this and the clearances maintained by means
of XiTRACK edge restraint beams.
This scheme has solved the drainage issues
originally present on site and continues to
perform well.
14. Page 12
3.20 Syston North Junction
Here lateral track stability problems are
aggravated by the tight radius of the turnout
which, although the line speed is relatively low,
does lead to significant lateral forces.
End restraint plates had been used but failed to
maintain the alignment and so an alternative was
sought.
XiTRACK application was completed within
schedule and subsequent monitoring has
confirmed that the treated areas have performed
as expected.
3.21 Knighton Junction
XiTRACK treatment was designed to give a
polymer loading leading to a maintainable,
improved alternative to end-plates for improving
the lateral stability of the junction.
XiTRACK polymer application was completed
within schedule and subsequent track recording
train runs show the alignment to be satisfactorily
retained.
3.22 Keadby Bridge Abutment Reconstruction
Keadby was another major construction scheme
where XiTRACK was utilised. The bridge was
replaced in 2003 and since construction there
had been alignment problems due to movements
within the abutments and substructure arising
from train loading and bridge movements. During
the planned renewal of the abutments during a
blockade over Christmas 2006, XiTRACK
treatment was applied to produce geocomposite
reinforcement of the transitions on both the East
and West abutments at this important structure.
15. Page 13
3.23 Balavil Burn and Gynack Burn
Two bridges on the Highland Main Line at
Gynack and Balavil near Kingussie are prone to
flooding causing heavy ballast contamination and
potential wash-out, leading to track defects,
disruption and subsequent delays.
A XiTRACK scheme was devised for each of the
bridge transitions to help prevent ballast being
washed out under the sleepers during such
periods of flooding. This gives protection to the
ballast under the sleepers permitting any water to
pass through the geocomposite but allows all
forms of conventional maintenance to occur.
The jobs were completed on time and each site now has proven enhanced protection against
ballast wash-out.
3.24 Falkirk Tunnel PACT System Transitions
In order to reduce the dynamic load on the run-
on to the concrete slab-track, a stiffened
transition was necessary. It was known that the
concrete track transition structure had
deteriorated and in addition the site suffered
from water ingress problems and the XiTRACK
design had to accommodate these effects.
A suitable XiTRACK design was installed and
performs as expected.
3.25 Tottenham South Junction
A complex scheme of vertical and lateral
XiTRACK reinforcement of the transition area
was designed to improve the performance under
local heavy passenger and freight loading and
particular attention was paid to the ballast on the
bridge deck itself near to the toes of the
Switches and Crossings.
16. Page 14
3.26 Purfleet Deep Wharf Level Crossing
The level crossing was showing signs of bearing
failure, pocketing and rutting due to the weak
formation and the very soft Alluvium clays known
to exist in the sub grade. In view of the current
and anticipated future loading conditions, along
with needing to minimise line closure time, a
XiTRACK treatment was considered desirable in
order to provide a long-term cost effective
solution.
A XiTRACK design was prepared for the site
and polymer applied in the specified loading
pattern and, including all groundworks, the site
was returned to full rail and road traffic after a
total closure time of only three days.
3.27 Bletchley
Switches and Crossings at Bletchley were
treated to correct vertical and lateral stability
problems on this high-speed section of the West
Coast Main Line. The site had been a major
maintenance headache for some time with
imposed speed restrictions until XiTRACK was
applied.
This site continues to perform and led to
additional schemes being implemented in the
surrounding area.
3.28 Worplesdon Hop Garden
The XiTRACK technique was used to reinforce
and stabilise the vertical bridge transitions for
the Hop Garden Bridge on the Up Guildford line
near Worplesdon Station. XiTRACK was used to
stabilise the transition in its current configuration
to help prevent further deterioration of the track
geometry. The site was treated to allow full
maintenance if required using manual
techniques.
No vertical re-alignment has been required since
treatment.
17. Page 15
3.29 Norwich – Ely
XiTRACK treatment removed the persistent
lateral track faults around these transitions
where tamping is difficult or impossible and no
lateral re-alignment has been needed since the
application.
The treatment area was adjacent to a river and
all requirements of the Environmental Agency
were met.
3.30 WCML Bridge Resonance Programme
XiTRACK Polymer was applied to ballast on a
series of bridges on the West Coast Main Line
in Network Rail’s Test Site A, in the Trent
Valley and in Scotland.
The bridges in the series were usually based on
a steel plate decking and had been found to be
subject to pre-resonance problems at normal
passenger train speed. They had been shown
to be susceptible to ballast movement due to
induced excitement with consequent loss of
track alignment. This problem had been
demonstrated to be likely to get worse with
Pendolino increased line speeds.
This was an effective temporary solution until the XiTRACK was broken out during the renewal of
the bridges during the upgrade of the route.
