Roadscanners Publication 2003 Tyre Bales on the B871

Roadscanners Publication 2003 Tyre Bales on the B871

ROADSCANNERS RESEARCH REPORT
THE B871 TYRE BALE PROJECT
The use of recycled tyre bales
in a lightweight road embankment
over peat
2
Colin Mackenzie, Timo Saarenketo
THE B871 TYRE BALE PROJECT
The use of recycled tyre bales in a lightweight road embankment over peat
Research report
Roadscanners
Rovaniemi 2003
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Abstract
This research report documents the construction of a road embankment on the
B871 Road in Sutherland, Scotland. This lightly trafficked road is built over deep
and weak peat and has been subject to subsidence. Because of a major increase
in traffic expected from timber extraction a 50 m long section of the road was
excavated and replaced with a lightweight embankment of 350 compressed tyre
bales.
A number of practical lessons have been learned from the project and these are
detailed together with suggestions as to further trials and uses of tyre bales in
embankments. The high porosity of a bale embankment has also been identified
as a key property that may have considerable potential for application in
sustainable drainage schemes.
Tyre bales are a novel product in the UK and it is recommended that it is best to
advance their use in civil engineering by carrying out well documented small to
medium scale trials, such as the B871 project, to build up confidence in a gradual
but sustainable way.
In particular it is recommended that research is carried out on:
•
•
•
•
•
Alternative interlock arrangements of tyre bales
Alternative types of infill material
Minimum depths of cover for satisfactory performance under heavy loads
Reinforcement of bales at intermediate and lower levels on soft ground
Drainage and water retention properties in service
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CONTENTS
1 INTRODUCTION .............................................................................................10
2 BACKGROUND...............................................................................................11
2.1 TIMBER EXTRACTION ....................................................................................11
2.2 IDENTIFICATION OF THE PROBLEM SECTION ....................................................12
3.1 NEW ROAD CONSTRUCTION ..........................................................................15
3.2 DEVELOPMENTS IN THE MAINTENANCE OF EXISTING ROADS OVER PEAT...........15
4 TYRE DISPOSAL: AN ENVIRONMENTAL CHALLENGE .............................17
4.1 THE EC DIRECTIVE ......................................................................................17
4.2 PRODUCTION OF TYRE BALES .......................................................................18
4.3 PROPERTIES OF THE TYRE BALE PRODUCT ....................................................19
4.4 COST OF TYRE BALES ..................................................................................21
4.5 THE LEGAL POSITION ...................................................................................22
5 DESIGN OF THE B871 TYRE BALE PROJECT ............................................23
5.1 EXTENT OF THE PROJECT .............................................................................23
5.2 GROUND INVESTIGATION ..............................................................................23
5.3 DESIGN CONSIDERATIONS ............................................................................24
6 CONSTRUCTION PROCESS..........................................................................26
6.1 BYPASS ROAD CONSTRUCTION .....................................................................26
6.2 HANDLING OF TYRE BALES ...........................................................................27
6.3 CONSTRUCTION SEQUENCE ..........................................................................28
6.4 INSTALLATION OF SETTLEMENT MONITORING RODS .........................................29
6.5 CULVERT INSTALLATION................................................................................30
6.6 COMPLETION OF PAVEMENT STRUCTURE .......................................................30
6.7 SUBSEQUENT WORKS ..................................................................................31
7 RESULTS OF MONITORING ..........................................................................33
7.1 EMBANKMENT SETTLEMENT ..........................................................................33
7.2 BALE COMPRESSION ....................................................................................35
7.3 CULVERT SETTLEMENT .................................................................................35
7.4 ASSESSMENT OF SETTLEMENT ......................................................................36
7.5 SETTLEMENT PROBLEM ON APRIL 2003 .........................................................37
7.6 SETTLEMENT PROBLEM SEPTEMBER 2003.....................................................38
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8 LESSONS LEARNED FROM THE PROJECT ................................................41
8.1 GENERAL ....................................................................................................41
8.2 GROUND INVESTIGATION ..............................................................................41
8.3 HANDLING ...................................................................................................41
8.4 BALE DIMENSIONS ........................................................................................42
8.5 JOINTS BETWEEN BALES ...............................................................................42
8.6 INFILL BETWEEN BALES .................................................................................43
8.7 GEOTEXTILE FABRIC.....................................................................................43
8.8 STEEL MESH REINFORCEMENT .....................................................................45
8.9 LAPS IN STEEL MESH REINFORCEMENT .........................................................45
8.10 INSTALLATION OF SERVICES ........................................................................45
8.11 MARKING AND RECORDING OF TYRE BALE EMBANKMENTS .............................46
8.12 SURFACE FINISHES AND TOLERANCES ..........................................................46
8.13 BALE TIE WIRES ........................................................................................46
8.14 CHEMICAL EFFECTS ....................................................................................46
8.15 POROSITY AND PERMEABILITY OF TYRE BALES .............................................47
8.16 DEVELOPMENTS IN THE LEGAL POSITION......................................................47
9 POSSIBLE FUTURE DEVELOPMENTS.........................................................48
10 CONCLUSION...............................................................................................49
BIBLIOGRAPHY ................................................................................................50
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ACKNOWLEDGEMENTS
The preparation of this research report has relied heavily on the constructive
dialogue and exchange of information between the client, Highland Council,
supplier Northern Tyre Recycling (UK) Ltd and Roadscanners. Thanks are due
to the Director of TEC Services at The Highland Council and her staff, particularly
Ron Munro, Community Works Manager and Garry Smith, Engineer at the
Council office in Brora who were actively involved in the project at all stages.
Thanks are also due to Jonathan Simm at HR Walligford for permission to
reproduce in advance their recent research data on the properties of tyre bales.
Inverness and Nairn Enterprise gave assistance with the funding for the report
research and preparation. Finally this report would not have been commissioned
without the enthusiasm of Dennis Scott, Managing Director of Northern Tyre
Recycling (UK) Ltd and his determination to find beneficial end uses for his tyre
bale products in civil engineering.
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1 INTRODUCTION
The disposal of used tyres is a challenge to modern society brought into sharp
focus by recent changes in EC waste disposal legislation. Dumping of tyres in
landfill is no longer acceptable and innovative solutions must be found if the
problem is to be dealt with. Northern Tyre Recycling (UK) started production of
compressed tyre bales in 2000 and have been active in seeking new end uses in
civil engineering for their product.
In the Highlands of Scotland the construction and maintenance of roads across
deep peat has always been a problem. Lightweight embankments are an
attractive solution but the materials required have traditionally been costly. The
prospect of an economic source of lightweight tyre bales proved of immediate
interest to The Highland Council, which required to deal urgently with a section of
the B871 road in Sutherland that was sinking in to the underlying peat.
The B871 Tyre Bale Project was designed and managed by The Highland
Council TEC Service in the Sutherland Area office in Brora, Sutherland.
Construction was carried out by contractor Edward Mackay of Brora over a three
week period in December 2002, with additional works being carried out as
necessary by the Council Direct Labour Organisation during 2003.
This report has been commissioned by Northern Tyre Recycling (UK) (NTR) in an
effort to learn lessons from the project and to disseminate this knowledge as
widely as possible.
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2 BACKGROUND
2.1 Timber Extraction
The B871 road in Central Sutherland serves one of the most remote and sparsely
populated areas of the UK. Although lightly trafficked and serving few properties
along its 25 km length, it is a lifeline route connecting the scattered communities
of the Helmsdale and Naver river valleys and beyond.
In the 1950’s extensive timber planting was seen as a solution to the limited land
use opportunities, both in terms of improving the local economy and providing
some diversity on the vast upland moorland. Two large conifer forests was
planted near the B871 road by the government Forestry Commission. Little
thought was given then to the extraction of the ultimate timber crop as it would
have been inconceivable at that time that the narrow and winding single track
road would stay unimproved for the next 60 years.
For many years it was thought that it might be uneconomic if not impossible to
get the timber to market but strenuous efforts were made by The Highland
Council (the Roads Authority) and Forest Enterprise (the commercial arm of The
Forestry Commission) to deal with this problem as the forests reached maturity.
Eventually a unique partnership was formed between these bodies with an
agreement that timber could be extracted along the B871 to Kinbrace. It would
then be transferred to the North Highland Rail Line at a purpose built railside
loading bank, constructed in 2002 with EC assistance. The B871 would be
monitored to see how it performed under the huge increase in traffic, and to see
what lessons could be learned from this.
This partnership agreement between the Council and Forest Enterprise
recognized their shared interest in the cost effective management and
maintenance of the B871 to ensure that in remained unrestricted to both timber
and normal public traffic. There has traditionally been a wide difference of
approach between forestry and local authority civil engineers and this provided
an opportunity to see what forest road techniques might have an application on a
lightly trafficked public road. The intention was that B871 would be monitored to
see how it performed under the huge increase in traffic and to share information
on maintenance solutions that would be low cost, innovative yet “fit for purpose”
rather than costly and over designed.
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2.2 Identification of the Problem Section
In 1997 The Highland Council engaged in an EC supported Northern Periphery
ROADEX programme to exchange technical information between roads
authorities in Scotland, Norway, Sweden and Finland. Considerable advantage
was gained from this exchange in an increased awareness of the techniques
available for assessing the condition of fragile and failing roads.
In order to properly monitor the B871 and a part of B873 a baseline survey had to
be carried out and Roadscanners were commissioned to do this. Roadscanners
carried out a Ground Penetrating Radar survey of the road and integrated this
with earlier information from:
•
•
•
•
A Falling Weight Deflectometer (FWD) survey of pavement structure
stiffness carried out by Scott Wilson Pavement Engineering
A High Speed Road Monitor (HSRM) survey of roughness and rutting
carried out by WDM
Pavement cores at regular intervals carried out by Scott Wilson Pavement
Engineering
Video recording of the road made by Highland Council
Roadscanners analysed this data using Road Doctor™ software and provided
the Council client with detailed information about current road condition, road
structures and their stiffness and subgrade soil quality and giving an indication of
the weakest sections of road. This could then be used as a basis for
maintenance planning and future monitoring of the road. The results were
published in the form of GIS maps in a written report and power point show
(Figure 1).
One section of road near Loch Rosail was in particularly urgent need of
strengthening, the pavement having sunk into the 6 m deep underlying peat
(figure 2). This section was frequently covered by up to 200 mm of water as it lay
at or below the moorland water table. This section of road is the subject of this
report.
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Loch Rosail test section
Figure 1. Risk analysis map of B871 Kinbrace - Syre and location of Loch Rosail
test section. The risk classification is from class 0 (no risk of damage) to class 3
(severe pavement damage will appear immediately after timber haulage starts).
Figure 2. Loch Rosail test road section. Pavement surface is located at the
ground water table level and frequently road was covered with 200 mm thick
water.
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Figure 3. Road Doctor GPR profile over Tyre Bale trial section. GPR profile
shows that the embankment is about 1.5 m thick in thickest section and
bituminous layer could be found from as deep as 0.7 m.
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3 TRADITIONAL SOLUTIONS FOR BUILDING ROADS ON PEAT
3.1 New Road Construction
Peat has proved a major impediment to road construction in the Northern
Highlands throughout the last two centuries but particularly in the last 50 years
when a major programme of road widening and improvement was carried out.
Early practice was to leave shallow depths of peat in place although this
inevitably resulted in eventual pavement deformation. On deeper sections
reinforced concrete slab rafts were sometimes used, with some limited success.
In West Sutherland timber fascine rafts were used in the 1950’s and early 1960’s.
These were formed from small diameter conifer tree trunks placed on the peat in
two orthogonal layers, and overlain by capping and pavement construction. Cleft
chestnut paling fencing, rolled out on the peat, was tried as an alternative to
fascines in some places. This had little strength but acted as a separation layer
long before the advent of modern geotextiles.
By the late 1960’s it was clear that the “floating” solutions that had been tried all
suffered from similar problems of deformation or settlement, requiring costly
resurfacing to restore shape and profile. With the advent of improved excavation
techniques including hydraulic excavators it became easier and more economic
to dig out all the peat, sidecasting it beside the roadworks. The resulting void was
backfilled with locally won rockfill. This became the norm for new road
construction in the area in recent decades.
3.2 Developments in the Maintenance of Existing Roads over Peat
Up until about 15 years ago the options used for the maintenance of roads over
deep peat in the Highlands were relatively limited. One was to dig out the section
of failed road, preferably down to the hard, and rebuild it. High cost generally
precluded this option.
The other solution was to simply resurface the misshapen road. This could be
more readily accommodated in annual budgets and provided a short term
answer. Unfortunately, and almost inevitably, the increased deadweight resulted
in further consolidation and a return of the problem within a few years if not
months. It became increasingly recognized that other solutions must be tried,
even at the risk of failure. Fortunately some of these had already been used and
proved in other countries with similar deposits of peat.
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In 1991 the Highland Regional Council used experience gained in Scandinavia to
replace a sinking road on the A837 at Ledbeg in West Sutherland. This involved
the excavation of a 200m section of road that had sunk badly. As if to
demonstrate the failure of the traditional method of solving the problem it was
found that no less that 1.45 m of bitumen macadam surfacing had been added to
the road in its 30-year lifetime. This created a huge deadweight for the underling
peat to carry. Below this pavement structure was a layer of chestnut paling
fencing.
This heavy pavement material was replaced with lightweight aggregate fill and
capped with a new pavement construction. This has proved extremely
successful, with the road holding up well after 12 years of service (Roadex 2001).
In 2000 The Highland Council carried out rehabilitation works on a 1km section of
the B876 where it crossed Killimster Moss, in Caithness. The problem here was
settlement and cracking of a 60 year old reinforced concrete slab laid on top of
peat 2 m to 5 m deep. Using information obtained under the ROADEX
international exchange programme a Ground Penetration Radar survey was
carried out by Roadscanners and a severe stripping defects of bituminous layers
were detected around especially in the areas with failed concrete.
The designed solution involved improving the drainage, removing the existing
poor quality bitumen macadam overlay, sealing the concrete cracks and
replacing it with a 150 mm thick steel reinforced dense polymer modified bitumen
macadam pavement. Experience so far has been extremely positive (Roadex
2001, reference).
More recently surcharging (overload embankment) has been used on the A839
and A837 in Sutherland to deal with problem sections over deep peat. This
technique has been commonly used in Scandinavia. On the A839 at Raemore an
offset widening exercise on a single track road 10 years earlier had resulted in
gross tilting of the carriageway to some 10 %, creating a hazard to traffic. On the
A837 at Benmore previous attempts to add surfacing to a sinking section had
only exacerbated the problem, to the extent that the road surface was frequently
below the water table, by up to 0.3 m in flood conditions.
The surcharging technique in both situations involved loading the existing road
embankments with fill 2 m deep and leaving them unsurfaced under traffic for 2-3
weeks. The surcharge material was then recovered, the embankment regulated
with subbase and the pavement replaced. This surcharging has been successful
in accelerating the consolidation of the underlying peat to the extent that a
reasonable life before reshaping can be now be expected.
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4 TYRE DISPOSAL: AN ENVIRONMENTAL CHALLENGE
4.1 The EC Directive
The disposal of used tyres is a major environmental challenge to the international
community. The UK alone needs to dispose of some 40 million tyres per annum
of which about 25 % currently go to landfill. From July 2003 the EC Directive on
the Landfill of Waste banned the dumping of whole tyres in landfill, with only
limited exceptions. The use of shredded tyres in landfill will be restricted from
2006.
The processes for beneficial disposal of tyres include:
•
•
•
•
Reuse e.g. retreading (although the carcase will eventually end up in the
waste stream)
Mechanical treatment to reduce size e.g. baling, ripping, cutting, grinding
Reclaim technologies e.g. rubber reclaim, devulcanisation
As a fuel source e.g. cement kilns and energy generation
The products arising from mechanical treatment are of most immediate interest
from a civil engineering point of view. These have potential for replacing
aggregate at a time when quarried materials are becoming more scarce and
costly. These products are:
•
•
Bales produced from whole tyres compressed and banded
Cuts, Shreds and Chips: irregular pieces of used tyre with sizes greater
than 300 mm in size, 50 mm-300 mm in size and 10 mm-50 mm in size
respectively
Northern Tyre Recycling (UK) are based in the Scottish Highlands and have
imported a portable truck tyre baler from the US. Using this NTR have baled
some 390,000 tyres in the last two years and have supplied bales to a number of
civil engineering applications such as haul roads, slope and river bank
stabilisation.
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4.2 Production of Tyre Bales
The tyre bales are produced by Northern Tyre Recycling at their depot outside
Inverness. However the mobility of their unit means that it can easily be towed to
a used tyre stockpile to minimise transport costs. This is particularly attractive
where stockpiles are at a remote location or where a suitable end use for the
bales can be identified locally. The unit has already visited some of the Scottish
Islands.
The number of tyres in each block varies, depending on the sizes of tyres being
compressed, as these can include all types from small car tyres to 1.5m outside
diameter earthmoving plant and tractor tyres. Between 100 and 120 tyres are
normally compressed into a single bale.
The tyres are fed by hand into a 1.5 m by 1.2 m chamber and compressed by
hydraulic rams (figure 4). Before release of compression the bales are tied with
5No bands of 9 gauge high tensile galvanized high tensile wire round their
shortest dimension. The bales, weighing about 0.85 tonne each, are removed by
forklift truck to storage.
Figure 4. Tyre Bale production at Northern Tyre Recycling site.
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4.3 Properties of the Tyre Bale Product
The standard bale size is a nominal box shaped 1.5 x 1.2 x 0.85 (1.53 m3) but
experience on the project showed that the effective size was slightly greater at
1.5 x 1.5 x 0.85, ie in plan they appeared square rather than rectangular. The
density of each bale obviously depends on the number and type of tyres
compressed in to it. The baling machine manufacturer quotes 250 to 600 kg/m3.
HR Wallingford Ltd are currently engaged on a research project on the
sustainable use of post-consumer tyres in port, coastal and river engineering. As
part of this they tested the properties of two bales provided by NTR, with the
results shown in Table 1.
Table 1. Properties of tyre bales produced by NTR (with acknowledgement to HR
Wallingford).
Property
Total Volume (m3)
Porosity (%)
Bulk Density (Kg/m3)
Weight of Bale (Kg)
Volume of tyre material (m3)
Solids as % of whole
% of voids sealed
Value
1.09 – 1.25
50 – 56
580 – 655
712.5 – 725
0.54 – 0.55
0.44 – 0.50
10 - 15
An important outcome of this information is that the true volume of the bale,
measured wrapped, averages 1.17 m3, considerably less than the nominal
volume of 1.53 m3. This is clearly as a result of the bales not being a true box
shape but having curved convex ends, as can be seen in Figure 5. This means
that, when bales are stacked together in an embankment voids round the outside
of the bale are likely to comprise 25 % of the total volume. Note that this does not
include the voids within the bale itself which has a porosity of over 50 %.
The bulk density of the NTR bales as measured (average 618 kg/m3) is rather
more than the 250 - 600 kg/m3 quoted by the baling machine manufacturer.
However if it is recalculated on the basis of the nominal volume rather than the
actual volume the figure is 470 kg/m3. The realistic value for a bale embankment,
without the voids filled but compressed under its own deadweight, would appear
to be somewhere in between, say 550 kg/m3.
A further reassuring outcome of the HR Wallingford research is that the bales do
not have a problem with buoyancy. At the time of the B871 project the only
evidence on this was anecdotal, NTR having placed a bale in the sea which
reportedly sank. Given that the specific gravity of natural rubber is 0.91 and the
potential for air being trapped in a bale, there was legitimate concern about this
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issue. However the Wallingford research has shown that the specific gravity of
tyre material is in fact greater than unity as it comprises materials other than
rubber, including 15 – 25 % by weight metal. Furthermore only 10 – 15 % of the
tyre bale voids were found to be sealed.
Figure 5. A stockpile of tyre bales, showing the voids caused by convex ends.
Table 2. shows a comparison with other types of compacted lightweight fills, with
gravel comparison:
Table 2. Unit weighs of materials used on road structures resting on peat.
Product
Tyre Bales
Tyre Shreds
Lightweight Aggregate
Expanded Polystyrene
Gravel
Unit Weight (kg/cum)
250-600
500-600
300-600
15-30
1900-2100
Apart from low weight tyre bales have a number of other useful engineering
properties, including the high porosity mentioned above, high permeability and
low thermal conductivity.
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4.4 Cost of Tyre Bales
The basic cost of a bale includes:
•
•
•
•
The cost of acquiring the waste tyres, (which may be negative)
The cost of tyre collection, bale manufacture and storage
The cost of delivery to the end user
Profits and overheads, including compliance with relevant waste disposal
regulations
With the banning of landfill, the problem of used tyre disposal is a pressing one
for the new tyre supplier who is likely to have to pay to make arrangements to
dispose of the old tyre. This cost of will obviously be passed on to the consumer
and will become part of the essential income stream to the baler. At present in
Scotland, some tyre suppliers have a clearly identified charge to the consumer of
£0.50-£1.00 for disposal of each carcase, others make allowance in their overall
prices.
The current ex works cost of a tyre bale is approximately £10-15 (table 3), which
works out at £5-10 /m3.
Table 3. Ex works costs for typical road materials used on roads resting on peat.
Product
Tyre Bales
Tyre Shreds
Lightweight Aggregate
Expanded Polystyrene
Gravel
Ex Works Cost (£/cum)
5 - 10
10 - 20
40 - 60
50 - 150
8 - 12
These prices must be viewed as only indicative as they will vary significantly
depending the location and size of project. Haulage costs to site have also to be
taken into account. The cost of gravel includes the Aggregate Levy, an
environmental tax on newly excavated materials to encourage recycling. At time
of writing this is £1.60 per tonne.
It can be seen from these figures that the tyre bale product is very competitively
priced, particularly when its lightweight is taken into account. Whether that
remains the case is likely to depend on:
•
•
•
•
Market forces once the effects of the EC Directive bed down
The range of beneficial uses that can be found for tyre bales
Demand for the product
Any increase in the Aggregates Levy.
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4.5 The Legal Position
The Scottish Environmental Protection Agency (SEPA) is the regulatory authority
in Scotland for waste management and licensing. When approached in 2001,
SEPA took a constructive view on the production and use of tyre bales. They
considered the production process was eligible to be registered for an Exemption
from the Waste management Licensing Regulations. At the time of construction
there appeared to be no requirement for the Council to seek any special
exemption or license for the use of the tyre bale product in the embankment.
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5 DESIGN OF THE B871 TYRE BALE PROJECT
5.1 Extent of the Project
Having identified the problem section of the B871 near Loch Rosail The Highland
Council designed a scheme to allow for the removal of the existing sunken road
construction over the peat hollow and its replacement with a lightweight
embankment of tyre bales. It was decided to raise the design profile by up to 1m
above the existing road to keep the surface above the water table, allowing for
some eventual settlement.
The overall length of the regrading scheme was 100 m with tyre bales being used
over the central 55 m.
5.2 Ground Investigation
The site investigations were made in order to get information about the existing
road structures and thickness of the peat deposit. A good indication of the
existing road construction was obtained from the Roadscanners ground
penetrating radar analysis (see figure 3). Because of the narrowness of the road,
and the weakness of its structure and the underlying peat the excavation of trial
pits was ruled out as being likely to seriously damage the road. Peat probes
were taken adjacent to the road and they indicated a depth to the hard of up to
6.5 m. Figure 4. provides information about peat depth in the area.
Loch Rosail Tyre Bale Trial - Peat Depth (m)
10
8
6
4
2
0
-2
-4
-6
-8
-10
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
-1.4
-1.6
-1.8
-2
-2.1
-2.2
-2.4
-2.6
-2.8
-3
-3.2
-3.4
-3.6
-3.8
-4
-4.2
-4.4
-4.6
-4.8
-5
-5.2
-5.4
-5.6
-5.8
-6
-6.2
-6.4
-6.6
Figure 6. Peat thickness in Loch Rosail test area. The Tyre Bale trial
embankment area is –4.5 - + 4.5 m (black lines).
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5.3 Design Considerations
The design of the replacement embankment assumed a tyre bale density of 550
kg/m3 compared to 2000 kg/m3 for the 1.3 m deep existing road construction
being replaced. The proposed 450 mm thick road and verge construction was
also assumed to have a density of 2000 kg/m3.
This indicated that, despite raising the road profile a reduction in the
embankment weight per square meter of about 30 % could be expected.
The design assumed some 320 tyre bales would be required, placed in two
layers each 0.85 m thick. The upper layer would be 5 bales wide and the lower 6
bales wide, creating a staggered joint between the bales in the different layers in
the transverse direction. Consideration was given to staggering the joints in the
longitudinal direction but this was ruled out as it would make the installation of
rods to monitor deep deflection extremely difficult. For simplicity the transverse
rows of bales were therefore to be laid directly one on top of the other. Figures 7
and 8 provide longitudinal section and cross section CAD drawings about the
object.
As infill to the interstices and any gaps between the bales 110 m3 lightweight
aggregate was specified. This was available from Optiroc ExClay Ltd at a
reasonable cost, being surplus from an earlier contract. The whole of the bale
embankment was to be wrapped in a lightweight 95 g/m2 Loktrak geotextile
fabric.
Figure 7. Longitudinal section showing tyre bale layers (CAD drawing by Gary
Smith, Highland Council)
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Figure 8. Cross section A- A in Loch Rosail tyre bale site (CAD drawing by Gary
Smith, Highland Council.
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6 CONSTRUCTION PROCESS
6.1 Bypass Road Construction
The Council held a meeting at Kinbrace to explain the proposals to the local
community who expressed interest and support for the project in principle but had
concerns about the possibility of the existing road being closed during
construction. Because of the remoteness of the area emergency vehicles might
have to make a 90km detour round any closure.
The Council gave an undertaking not to close the road and engaged plant and
labour local contractor Edward Mackay Ltd of Brora, a firm with considerable
experience in the construction of roads on peat. Being a single track road the first
matter to be addressed was how to carry out the works whilst keeping traffic
moving.
Experience has shown that if a tracked machine is driven carelessly on to weak
moorland such as this it is easy for it to break through the fragile surface. Timber
sleeper mattresses can be used to spread the machine load but they are not
infallible. The fluidity of the 6 m deep peat in this situation was such that if a
machine did sink through, it would be a major earthmoving task to extricate it.
The contractor therefore decided to keep the construction plant on the line of the
existing road where the underlying peat would have greatest strength.
The moorland beside the road formed part of a Site of Special Scientific Interest
in relation to its environmental value and the approval of Scottish Natural
Heritage was required for any works required off the existing road. They
recognized the practical difficulties of construction and were cooperative about
the location of a temporary bypass road, requiring only that it be removed entirely
at the end of its use.
The contractor started by building the temporary bypass some 120 m long across
the moorland parallel to but 10 m distant from the existing road. This bypass was
constructed of 450 mm of as dug rockfill on top of the geotextile fabric separation
layer laid directly on the heather clad surface.
The bypass road was subject to a 7.5 tonne weight restriction but is soon
became apparent that the underlying peat was so fluid that it was moving both
laterally and downwards under the deadweight of the fill alone. By the end of the
3 weeks of the contract parts of the bypass road had sunk by up to 1 m, and was
flooded much as the original road had been.
27
Figure 9. Bypass road had rapid settlement during the construction project.
6.2 Handling of Tyre Bales
An immediate problem to be solved was that the tyre bales were more difficult to
handle that expected. They did not have specific lifting points so initially lifting
chains were used, hooked in to the rim bead of a tyre at each end of the bale.
However because of the high compression of the tyres and the variation in their
size this was not always easy and was time consuming. A fabric sling was
obtained but the only place it could be secured was through the tie wires round
the bales. This was tried with initial success until one of the bales burst open and
its tyres spilt out.
This was an instructive mishap in that, contrary to what might be expected, the
tyres did not spring violently back to shape. This supported anecdotal reports
that baled tyres do lose some of their “memory” when in a compressed state and
spring back only slowly when released. The large pile of tyres released provided
proof, if any were needed, of the space saving benefits of the compressed
product.
It was clear that a better method of lifting the bales had to be found. NTR had
recommended that a logging grab was the best means to use, and in fact the
bales had been delivered to site by a timber wagon, fitted with standard lifting
gear including a 360 degree swivelling grab. Unfortunately because of limitations
of reach this vehicle could not be used at the working face so an additional
crawler excavator had to be requisitioned fitted with a similar grab. This proved
the perfect tool for lifting the bales, preventing damage to the tying bands and
enabling them to be rotated into place without manual intervention.
28
Figure 10. Machinery used in building Tyre Bale structure.
6.3 Construction Sequence
Once the bale handling problem was resolved, work progressed in an efficient
and methodical manner as follows:
•
The forward excavator dug to formation level, approximately 1.5 m below
the existing road, over a bay length of 5 m. The material was removed to
tip by dumper.
•
Operatives placed a strip of geotextile across the cross section, leaving
surplus for wrapping over the bales.
•
Grab machine at rear placed lower row of tyre blocks in place, with
assistance as required from forward machine to push them tightly into
place.
•
Lightweight fill was dumped over bales and allowed to percolate the
interstices.
•
The second (upper) layer of blocks was put in place and dressed off with
lightweight fill before operatives gathered loose geotextile to complete
wrapping of bale group, with overlap on top.
29
•
The rear excavator spread a 3 m wide layer of fine rockfill over the
geotextile, to provide a working platform for moving forward to the next
bay.
The construction and capping of the 50 m long tyre bale embankment, utilizing
some 350 bales, took two weeks of the three week contract period to complete.
6.4 Installation of Settlement Monitoring rods
In order to assess the extent of any movement of the bale embankment
monitoring rods were installed at approximately 10 m centres in each verge 1m
from the edge of the road.
These rods comprised round steel bars sufficiently long to protrude above the
final verge. They were welded at the lower end to a square steel plate.
The rods were installed in the appropriate lateral position, at a convenient
longitudinal position to suit a butt joint in the tyre bales. The base plate was
placed on the underlying geotextile, ensuring that any settlement of the bale
would draw down the rod.
In order to provide additional security of monitoring and in particular to determine
if there was any significant separation or compression of the two bale layers, a
further 4No monitoring tubes were installed. These comprised a steel tube
welded to a square steel base plate, the latter being drilled with a hole concentric
with the tube.
These tubes were threaded over the monitoring rods, after installation of the
lower bale layer, so that the base plate could be trapped between the two layers.
The tubes were shorter than the rods so that the rod protruded above the tube,
enabling levels to be taken on both.
There was no particular difficulty with installing these devices although there was
a tendency for them to be damaged by careless machine operation.
30
Figure 11. Monitoring steel rods were placed on the tyre bale joints both sides of
the road. Photo presents also the filling technique with lightweight gravel.
Monitoring roads can be seen on right joint. Smaller red rods are installed on the
bottom of the bales and black tube rods between the two tyre bale layers.
6.5 Culvert Installation
Although the roadside drainage was by open ditch along each side of the road, a
300 mm diameter rigid plastic pipe was installed to provide a measure of balance
if cross road drainage became necessary in the future. This was conveniently
placed at a butt joint in the tyre bales and surrounded by lightweight fill.
6.6 Completion of Pavement Structure
As soon as the bale embankment was installed the rockfill layer was topped up to
250 mm deep and dressed off to level. A nominal layer of A252 welded
reinforcing mesh (8 mm bars at 200 mm centres) was included in this layer. It
was considered that this mesh would provide some additional strength to the
capping layer, helping to tie it together during the significant bedding in
movements that could be expected. This technique has been used in Finland in
similar weak subsoil situations.
31
An excavator then spread a 100 mm layer of Type1 sub-base on top of the
rockfill to provide a running surface. This enabled the road to be reopened to
public traffic.
Work then moved to the removal of the bypass road, the rockfill used in its
construction being recovered and placed as verge construction on the main road.
Subsequently the verges were further dressed off with peat.
Figure 12. Unbound structures over tyre bales. Steel reinforcement is installed in
the sub base.
6.7 Subsequent Works
After 3 months of traffic the Type1 sub-base road surface was becoming
increasingly loose and a 50 mm thick layer of fine sand/gravel was added
through a paving machine to bind the running surface, particularly for the heavy
timber traffic that started that month.
To further bind and waterproof the surface two layers of surface dressing were
applied in July 2003, using 10 mm chippings and 2 litres/m2 bitumen spray on
each layer.
32
Figure 12. Loch Rosail tyre bale structure after completion of pavement.
33
7 RESULTS OF MONITORING
7.1 Embankment Settlement
Monitoring of the embankment settlement commenced on 11 December 2002,
with leveling of the five rods and three tubes installed by that date. Further
leveling of these was carried out two days later, with the first complete leveling of
the total 12 rods and 4 tubes being carried out when the road was opened on 19
December 2002. Placing of rockfill verging was taking place at that time.
Additional leveling was carried out on 6 January 2003, following which the
contractor completed the final verging. The leveling was repeated at
approximately monthly intervals thereafter, with the latest results being taken on
10th July 2003.
Figure 13. presents a contour map of settlements measured in the Tyre Bale trial
site untill April 8th. Figure shows that the highest settlement was measured on the
left side of the embankment at 85 m. When comparing this to peat thickness info
(see figure 6) this was quite surprising because the peat was thicker in the right
side of the road. In general the correlation between measured settlements and
peat thickness was quite good, however.
It is clear from this graph that the settlement of the left hand side is much greater
than that of the right, in other words the new embankment was first tilting to the
left. This can also be seen from the figure 14, which compares the rate and
extent of settlement of the left and right hand pins at chainage 85 m. This tilting is
still slowly continuing, which can be seen in figure 15, which compares the
settlement speeds on right and left side of the embankment during the time
periods after the construction. The settlement rate on the left sides are still
slightly bigger than on the right. However after April 8th 2003 the settlement rate
has been less than 0.5 mm/day, which means that during the next year the
cumulative settlements will be much less than 15 cm.
34
Loch Rosail Tyre Bail Trial - Cumulative Settlements 080403
-0.06
-0.08
-0.1
-0.12
4
2
0
-2
-4
50
-0.14
-0.16
-0.18
-0.2
-0.22
-0.24
-0.26
-0.28
-0.3
55
60
65
70
75
80
85
90
95
100
105
110
-0.32
-0.34
-0.36
Figure 13. Countour map of cumulative settlement in Tyre Bale trial structure in
April 08, 2003. The biggest settlement were recorded at 85 m on the left side if
the road embankment.
11-Sep
11-Aug
11-Jul
11-Jun
11-May
11-Apr
11-Mar
11-Feb
11-Jan
11-Dec
Cumulative Settlement Graph Chainage 85
Settlement (m)
0.000
0.050
ch 85 left
0.100
ch 85 right
0.150
0.200
0.250
0.300
0.350
0.400
0.450
Figure 14. Cumulative settlements at chainage 85 m in Loch Rosail tyre bale trial
site.
35
Average Settlement Rate per Day
5.00
4.50
Rate (mm/day)
4.00
Left
3.50
Right
3.00
2.50
2.00
1.50
1.00
0.50
19-Sep
19-Aug
19-Jul
19-Jun
19-May
19-Apr
19-Mar
19-Feb
19-Jan
19-Dec
0.00
Figure 15. Settlement rate in test site during time period a) construction –
January 28th 2003, b) January 28th – April 8th and c) April 8th – July 9th.
7.2 Bale Compression
There is little difference between the settlements of the 4 tubes and their
associated rods, consistently in the range 0-10 mm. This indicates that there has
been no great compression or separation of the bale layers.
The only exception was an isolated movement difference of 37 mm recorded at
Chainage 75 m left between 19 December 2002 and 6 January 2003. This
suggested compression of the lower bale by that amount. However given the
consistency of the other results it is thought this may have been a rogue value
indicating the bedding down of the monitoring tube base plate after placing of the
rockfill verging, rather than true bale compression.
7.3 Culvert Settlement
A remarkable feature has been the increasing curvature of the culvert pipe.
Within a month of installation it was noticed that water was flowing into both ends
of the pipe, indicating that the surface water was leaking in to the tyre bale mass.
It was clear that the pipe had bowed so much that the central slip joint must have
pulled.
Eight months later one end of the pipe rises steeply from the ditch showing the
extent of the curvature. The other end of the pipe is no longer visible.
36
Figure 15. Deflection of culvert outlet.
7.4 Assessment of Settlement
It is clear from the monitoring that the embankment has settled by up to 0.4 m
over seven months. However the rate of settlement has reduced steadily and it
is reasonable to assume that it is the normal consolidation of the underlying peat.
If a conventional rockfill embankment of equal dimensions but three times the
weight had been installed, the situation would have been considerably worse.
Of interest is the clear tendency for the embankment to slightly tilt to the left.
Given that the new embankment is centered on the old road this sort of
differential consolidation was not expected. The most likely answer appears to
lie in the construction of the temporary bypass road on the right hand side of the
new road. Immediately the bypass road was constructed it started to sink and
cracks were noticed in the peat between the bypass road and the existing road
suggesting that the peat was bulging and moving under the compressive load of
the bypass road. It is concluded that this had the effect of pre consolidating and
strengthening the peat on the right hand side of the new embankment, over the
three weeks the bypass road was in place.
37
Another explanation can be that a better drainage system was located on the left
side of the road where there were ditches and also the hill slope was to the left.
This better drainage in the left side allowed also faster settlement. The same
phenomenon could be seen also in the temporary road that had faster settlement
on the left side (see figure 9).
7.5 Settlement Problem on April 2003
On 25 April it became clear that two major sharp transverse settlements were
forming on the road near chainage 60 and 70 m (figure 16). Significant vertical
movement of the road surface could be seen during the passage of laden trucks
although, apart from the rutting damage, the road apparently recovered to its
original level when the vehicle had passed.
A few days later the road surface was excavated at the position of the rut near
chainage 60 m. It was discovered that the problem lay in a lack of shear
resistance where joints in the steel fabric reinforcement (2.4 m centres) coincided
with a joint in the wrapped bale mass (1.5 m centres). Because of the shearing
movement under traffic load road material flowed between the tyre bales and this
resulted a sharp settlement on the road surface.
This was repaired by stripping off the capping material over a 5 m section above
the joint and placing two additional sheets of steel mesh to provide additional
strength. The capping was reinstated and the repair has since worked well.
The cause of the rut at Chainage 70 was less clear but may have been related to
the adjacent culvert, which has suffered substantial movement as described in
Section 7.3 above. The surface over this rut was regraded and has since
performed satisfactorily.
38
Figure 16. A sharp transverse settlement in late April 2003 at chainage 70 m.
7.6 Settlement Problem September 2003
In September 2003 it became apparent that a regular pattern of settlement was
occurring which was clearly detectable when driving along the road. On visiting
the site after light rain this could be seen from the pattern of pools of water
retained on the surface. This is shown on Figure 17.
On measuring the distance between 11 of these depressions it was found that
they varied between 1.4 m and 1.7 m apart, with an average of 1.58 m. This is
remarkably close to the 1.5 m nominal dimension of the tyre bales in plan. On
measuring the distance between the next 5 depressions outwith the bale
embankment, the average dimension was noticeably higher at 2.0 m.
39
Figure 17. Pools of water at regular intervals on road surface 30 September
2003.
The obvious conclusion is that the surface irregularity is being caused by
settlement at the joints between the rows of tyre bales. Unlike the April
settlement problem at Chainage 60 it does not appear to be connected to the
spacing of the mesh reinforcement (2.4 m sheet size). Without further research it
is not clear what the exact cause is but it is believed to be one or a combination
of:
•
•
•
•
the lightweight fill slipping down the joints between the bales
groundwater pumping up the joints, weakening the road structure locally
the difference in compressibility between the infill and the bales
the dynamic movement of the bale structure.
Unfortunately this is one area where the bales are not behaving as predictably as
a conventional fill embankment. With the benefit of hindsight it would have been
better to have taken extra steps to ensure good interlock and load distribution
between the blocks. Options would have been:
•
•
•
additional reinforcement between and below the bales
an alternative infill material
greater cover over the bales.
40
At the time of writing The Highland Council has not decided on the best course of
remedial action. Roadscanners have suggested that a detailed Ground
Penetrating Radar (GPR) survey of the embankment is likely to give valuable
information on the relative positions of the capping fill, bale layers, lightweight
aggregate infill, underlying peat and any voids between these components. This
will be carried out in the near future.
Excavation into the bale mass to retrospectively install low level reinforcement is
unlikely to be realistic. Depending on the results of the GPR survey it is expected
that work to enhance the live load distribution properties of the embankment may
include:
•
•
Installing additional steel reinforcing mesh in the capping layer
Increasing the cover to the bales by adding lightweight fill
It is clearly undesirable to add significant extra weight to the embankment so
some of the existing capping layer and running surface may have to be stripped
off and replaced at a higher level. Any work of this type will pose practical
problems given the single track nature of the road and the need to keep traffic
running.
41
8 LESSONS LEARNED FROM THE PROJECT
8.1 General
The B871 tyre bale embankment has now been in operation for nine months. The
experience gained from its construction and maintenance so far suggests the
following are issues to be taken into account in considering the use of tyre bales
in similar and other civil engineering projects.
8.2 Ground Investigation
It goes without saying that a good ground investigation is essential to any civil
engineering project, and this project was no exception. A frequent grid of peat
probes around the existing road indicated soft peat consistently about 6m in
depth. The Roadscanners Ground Penetrating Radar run along the centre of the
road gave an excellent picture of the existing road construction and correctly
predicted the 1.3 m depth of construction below the existing road.
What was not anticipated was the fact that the road construction box was cut off
vertically at the edge of the road running surface. There was no road
construction of any sort under the verge and there was none of the lateral
dispersion of the original gravel foundation that might have been expected. With
the benefit of hindsight it explained the clear vertical movement crack which ran
along each side of the road, between the running surface and the verge, prior to
work starting.
It will be recalled that the project design assumed that heavy road construction
materials were being replaced with lighter weight tyre bales, resulting in a 30 %
saving in weight. In reality this was only true over the narrow 2.8 m width of the
existing road with the remainder of the bale embankment replacing only
saturated peat. The predicted saving in deadweight will not have been achieved
but the spread of dead and live loads over the greater width of the new
embankment is clearly working satisfactorily in practice.
8.3 Handling
The selection of appropriate plant for handling the bales is essential for efficient
installation and the rotating grab proved invaluable on this project. On a smaller
project it might be helpful if lifting points were provided on the bales so that
conventional lifting equipment could be used. Northern Tyre Recycling (UK) Ltd
can now supply bales of this type.
42
8.4 Bale dimensions
It is important to recognize that tyre bales do not have a fixed geometry like
bricks or concrete blocks. The sides and ends of the bales are slightly convex
making them difficult to measure exactly and this variability must be allowed for in
any design. This did not cause major problems on the B871 but where close
tolerances are needed the more generous the capping layer the easier it will be
to correct level differences.
Figure 18. Because of tyre bale dimensions there was a tendency that the bales
became easily concave.
8.5 Joints between Bales
The B871 design allowed for a stagger in the transverse joints between the bales
in the two layers. With the benefit of hindsight it would have been better to also
have had a stagger in the longitudinal direction. This might be slightly less
convenient from a construction point of view, requiring a stepped working face
and plant with a slightly greater reach. However it would offer considerably
enhanced shearing resistance and load distribution, and would have helped
prevent the problems experienced in April and possibly in September. Because
of this it is recommended that staggered joints be used wherever possible in
weak ground conditions or under traffic.
43
The plan shown in figure 19. shows a bond pattern that gives good interlock but
uses an extra bale every second row. Whilst it would be easy to build this pattern
in rows up the page, it might be difficult to build left to right as this would involve
threading bales into the gaps between those previously installed. The
practicalities of this are worthy of investigation on another project, as would any
difficulties of offsetting of the upper layer.
Figure 19. A proposed system for getting better interlock for tyre bales.
8.6 Infill between bales
Lightweight aggregate fill was used to fill the interstices between the bales prior
to them being wrapped in geotextile (see figure 18). This material had the
advantage of being clean and easy to use and obviously offers significant weight
savings compared to using conventional fine aggregate. This was attractive in
the extremely weak ground conditions on the B871 but it is costly and a design
judgment will have to be made in each case to see if the benefits compensate for
this. Angular crushed rock chippings, say 10-25 mm, will be a cheaper if heavier
option and will be likely to offer a good frictional bond between the blocks. Sand
infill is understood to have been used in the USA, washed into the interstices by
water jet.
8.7 Geotextile Fabric
It is not clear how much the geotextile fabric contributes to the overall strength of
the tyre bale embankment in a situation like this where the settlements are high.
The movements are such that, if the geotextile has not torn at the basal level, it
may well have slipped at the laps.
The geotextile did provide a useful separation layer, preventing contamination of
the bales and the lightweight infill. In addition it provided an invaluable working
surface when placed on the underlying soft peat, without which operatives would
have sunk up to their knees.
44
The project started with the bales being wrapped in individual transverse rows i.e.
the lap in the wrapping fabric was on top of the bale and transverse to the road.
This method of wrapping gave no continuity of fabric across the joint and is felt to
have been a significant contributory factor to the settlement experienced in April.
Later in the project the bales were wrapped with the fabric lapped along the
centre of the road, giving better continuity of the fabric.
This is the method that would be recommended. In weak ground conditions such
as here, generous laps of should be allowed to prevent loss of fines from capping
or infill, particularly where there is a risk of pumping occurring.
Figure 20. An example of possibly too short geofabric overlap. Even though a
new geofabric will be place on the top of old fabric, there is a risk that
embankment settlement and tyre bale movements due to traffic load may cause
that subgrade soil can squeeze up to bale joints. This photo shows also that the
edges of the embankment were resting on virgin peat and old road construction
was located only in the middle.
45
8.8 Steel Mesh Reinforcement
It is considered that the nominal steel mesh reinforcement was an extremely
valuable inclusion in the design, particularly in view of the high movements
expected here. The steel mesh might have given slightly better support if the
installation depth had been deeper than 10 – 15 cm. Ideal depth would have
been about 25 cm from the surface. Because of the tyre bale movements and the
settlement problems in April and September, steel mesh might have been a good
structure on the bottom and intermediate level as well as on the top of bales to
prevent them moving against each other.
As mentioned earlier this was based on experience in Finland where unprotected
mesh is used. With high levels of the use in the UK of road salt for deicing the
life of unprotected mesh must be considered although this has not been a
problem in Finland. Given the experimental nature of the B871 embankment this
is not a major issue but if there is a concern galvanised or epoxy coated mesh
can be considered.
8.9 Laps in Steel Mesh Reinforcement
The Finnish experience mentioned above suggests that it is best to ensure
transverse continuity of the mesh laid on the road embankment, to prevent the
road breaking its back. In accordance with this principle the sheets were laid on
the B871 with no attempt to lap or join them longitudinally. The failure in April
suggests a weakness in this approach when using tyre bales, particularly where
joints in the tyre bales can coincide with mesh joints.
It is recommended that further work be done to see if this difficulty can be
overcome by staggering the bale joints as suggested above, or by lapping the
mesh in some manner.
8.10 Installation of Services
Excavation through a tyre bale embankment would be a major task, not to be
undertaken lightly. If pipes and services require to be installed it is recommended
that they are placed outwith the tyre matrix as access for maintenance would
otherwise be extremely difficult. Depending on the circumstances this can be
achieved by increasing the cover over the bales to provide sufficient depth to
carry any services. The same difficulties would apply to the installation of
roadside furniture such as traffic signs, safety fences, lamp standards etc.
46
8.11 Marking and recording of Tyre Bale embankments
It is recommended that the location and extent of any tyre bale embankment
should be properly recorded and marked on site to ensure that it is not
accidentally damaged during routine maintenance such as ditching operations.
8.12 Surface finishes and tolerances
The B871 embankment is highly flexible because of the weakness of the
underlying peat. It is therefore not possible do draw any firm conclusions on the
ability of a tyre bale embankment to carry hard surfacing or urban landscaping
such as paviors, kerbs, slab paving etc. It is recommended that further trials
should be done on this aspect, using a bale embankment founded on material
other than weak peat.
Similarly the B871 has not been built to high tolerances, and the road is of such a
character that settlements and movements under traffic can be accommodated.
If bales are to be used under a high speed road requiring high surface tolerances
it would be best to do further trials or to research their use in other countries.
This would establish if high tolerance surfacing can be laid and maintained, and
what the minimum capping requirements are in such a situation.
8.13 Bale Tie Wires
The bale tie wires stood up well to the forces involved in handling and placing,
apart from the mishap when the single bale burst. Galvanised fencing wire can
have a life of over 30 years but it is not known what life can be predicted for the
tie wires underground and possibly under the action of deicing salt. This may not
be relevant in the long term if as is claimed the tyres do not rebound to their
original shape.
8.14 Chemical effects
Research on the long term effects of leachate from tyres reaching groundwater is
ongoing in a number of countries. It is understood that research so far indicates
that the leachate is unlikely to be a serious problem. No work on this aspect has
been undertaken on the B871 project.
47
8.15 Porosity and Permeability of Tyre Bales
The porosity of tyre bales and bale embankments were discussed in Section 4.3
above when it was calculated that some 25% of the embankment was likely to be
voids between the bales.
The theoretical volume of the B871 embankment was 500 m3, suggesting 125 m3
would be voids. It is interesting to note that the 110 m3 of lightweight infill
provided was fully utilised on the project, suggesting that, despite the mobility of
lightweight fill, some voids may have remained unfilled. This may not be
unconnected with some of the settlement difficulties discussed above.
Whilst completely infilling the voids may be difficult it must be recognised that the
high porosity of the bales themselves, taken with the inevitable voids round about
them create an attractive product in terms of drainage and water retention
capacity. The figures suggest that a tyre bale embankment will have a porosity of
over 60 % and potentially even more if it is loosely built for that purpose. Taken
together with the good permeability of the bales themselves this suggests
considerable potential for use in sustainable land drainage and retention
schemes. Further research will be required to determine the effective properties
in service and to identify any problems that might arise.
8.16 Developments in the Legal Position
It was stated earlier that The Scottish Environmental Protection Agency (SEPA)
had taken a constructive position on the production and use of tyre bales at the
time they were approached in 2001. However, more recently, it is understood that
the Environment Agency (the regulatory body in England) has taken a more
cautious view. This follows recent rulings by the European Court that throw some
doubt on exactly at what point in law tyres going through a baling process cease
to become waste but become a recycled product.
Until the legal position becomes clearer it is recommended that detailed
discussion with the regulatory body is essential at the outset of any project
involving the use of tyre bales. There is an international dimension to this
problem and from an engineering point of view it is vital that the position is
clarified for all concerned. If tyre bales are to become an established engineering
product, ways must be found to simplify their use within the constraints of the law
and sound environmental management.
48
9 POSSIBLE FUTURE DEVELOPMENTS
Tyre bales have already been used in a number of civil engineering applications
in the UK, including haul road construction, drainage and slope stabilisation. The
major project currently being undertaken by HR Wallingford to evaluate the use
of tyre bales as void fillers in sea defence works and river bank protection has
also been mentioned above and the full results of this are awaited with interest.
The previous Section suggested a number of issues that would benefit from
further investigation or trial and it is to be hoped that the knowledge gained from
such schemes is widely published.
Looking to the future it is interesting to note that an embankment the size of a
football pitch and 2 m in depth would need sufficient tyre bales to consume 10 %
of the tyres currently dumped in landfill in the UK each year. Large scale projects
of this type might be:
•
•
•
•
•
Embankments carrying roads across flood plains, wetland or peat
moorland
Raising and drainage of low lying agricultural land
Land reclamation
Sustainable drainage schemes using the permeability and storage
capacity of tyre bales
Infill to create public amenity land or large scale parking and utilizing the
above sustainable drainge properties
It is difficult to predict how quickly such large scale schemes can develop until the
tyre bale market becomes more mature. In the meantime it must be remembered
that this is an innovative product in the UK and it may be best to advance its use
in civil engineering by pressing on with small to medium scale trials, such as the
B871 project, to build up confidence in a gradual but sustainable way.
49
10 CONCLUSION
The B871 Tyre Bale Project has now been in operation for nine months and has
successfully dealt with public traffic, including 30,000 tonnes of timber traffic. It
has shown that it is possible to construct a lightweight road embankment over
exceptionally soft peat using recycled tyre bales. Remarkably, this small project
has found a new use for about 40,000 used tyres, 0.4 % of the annual UK tyre
throughput to landfill.
A number of practical lessons have been learned from the project and these are
detailed above, together with suggestions as to further trials and uses in
embankments. The high porosity of a bale embankment has also been identified
as a key property which may have considerable potential for application in
sustainable drainage schemes.
Tyre bales are an innovative product in the UK and it is recommended that it is
best to advance their use in civil engineering by carrying out well documented
small to medium scale trials, such as the B871 project, to build up confidence in a
gradual but sustainable way.
In particular it is recommended that research is carried out on:
•
•
•
•
•
Alternative interlock arrangements of tyre bales
Alternative types of infill material
Minimum depths of cover for satisfactory performance under heavy loads
Reinforcement of bales at intermediate and lower levels on soft ground
Drainage and water retention properties in service
50
BIBLIOGRAPHY
Carlsten, P. 1988. Peat, Geotechnical Properties and Uptodate Methods of
Design and Construction. State-of-the-Art-Report. Varia 215. Statens
Geotekniska Institut, Linköping Sweden, 35 p.
CEN Workshop Agreement CWA 14243: Post-consumer tyre materials and
applications (FINAL 18.3.02)
Evaluation of the Impact of Timber Transportation on Roads: B871 Kinbrace to
Syre and B873 South of Syre; Timo Saarenketo and Tomi Herronen;
Roadscanners Oy, 2001.
Roadex Multimedia CD rom www.roadex.org
Road Construction over Peat; A report of a Winston Churchill Travelling
Fellowship; Ron Munro, 1990.
Road rehabilitation of B876 Killimster Moss, Caithness; CR Guest; Highways and
Transportation, March 2002.
Saarenketo, Timo; Hietala, Kari; Salmi, Tiina 1992. GPR applications in
geotechnical investigations of peat for road survey purposes. In: Hänninen, P.,
Autio, S. (eds.) Fourth international conference on ground penetrating radar,
June 8-13, 1992, Rovaniemi, Finland. Geological Survey of Finland. Special
Paper 16, 293-305.
Saarenketo, T. 2001. GPR Based Road Analysis – a Cost Effective Tool for
Road Rehabilitation – Case History from Highway 21, Finland. In Proceeding of
20th ARRB Conference, Melbourne, Australia 19-21 March, 19 p.
Saarenketo, Timo. 2002. ROADEX – low volume road condition management in
EY Northern Periphery Area. Finncontact. Vol. 10 / No. 2. July 2002, p. 7-8.
Saari, J. and Saarenketo, T. 2002. Road Condition Management of Low Traffic
Volumer Roads in the Northern Periphery. A state-of-the-art report.
www.roadex.org
51
APPENDIX 1
Figure 1. Photo showing Northern Tyre Disposals Ltd (now Northern Tyre
Recycling UK Ltd) mobile tyre bale press.
Figure 2. Dennis Scott with tractor tyre in open press chamber.
52
Figure 3. Tyre chamber filled with 30 tyres, ready for for first press.
Figure 4. Bale compressed, doors open, tie wires being inserted.
53
Figure 5. Tie wires now looped, ready for pressure release.
Figure 6. Pressure off, bale ready for offloading to stockpile.
54
Figure 7. Showing bales in stockpile. Note voids between bales.
Figure 8. Another view of stockpiled bales, showing even greater voiding.
Visually the bales appear to be more rectangular on the tied faces. The untied
faces, which were at the ends of the compression chamber exhibit more of the
curvature of the original tyres.
55
APPENDIX 2
Figure 1. Existing B871 at site prior to start. Note subsidence, surface slippage
and edge failure.
Figure 2. Showing the Railside Loading Bank at Kinbrace where timber has to go.
56
Figure 3. Work starts with construction of bypass road.
Figure 4. First bales go in, on top of geotextile.
57
Figure 5. Second Row, showing monitoring rods in place below bale layer.
Figure 6. Bales delivered to site on timber truck.
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Figure 7. Transition wedge between single and double layers formed of
lightweight fill (covered by geotextile.
Figure 8. Monitoring tubes formed from 50dia tube, for placing over rods.
59
Figure 9. Timber grab on crawler excavator placing bales.
Figure 10. Showing right hand excavator moving up chainage digging out existing
road; left hand machine is placing bales towards it.
60
Figure 11. Placing lightweight aggregate fill by dumper. Note voids between
bales.
Figure 12. Extremely weak saturated peat underlay the existing road
construction.
61
Figure 13. As work progressed the bypass sunk into the peat 1.0m, despite being
subject to a 7.5 tonne weight restriction.
Figure 14. Capping in place, showing steel mesh reinforcement within it.
62
Figure 15. Road open to traffic, with bypass being removed.
Figure 16. A 50 mm layer of sand/fine gravel being added to bind the surface and
improve running quality.
63
Figure 17. Typical timber truck. A monitoring tube can be seen painted yellow on
left.
Figure 18. April 2003. Excavation showed localised rutting failure was related to
bale joint coinciding with mesh reinforcement joint.
64
Figure 19. August 2003. The extent of the culvert deflection is remarkable, and
not yet fully explained.
Figure 20. September 2003. Regular transverse rutting is clearly related to joints
in bale structure.