Tyre Bales as Lightweight Fill: Reducing Load on Weak Soils

Updated on: 24th February 2026 By:     Conor Murphy
Expert review by:     Kieran Donnelly

Tyre bales as lightweight embankment fill have become an established solution for one of geotechnical engineering’s most persistent problems: building stable road, rail, and flood defence embankments over soft or compressible ground. Where conventional granular fill would apply a load the weak subgrade simply cannot support, tyre bales reduce that stress by up to 70 per cent for the replaced depth, without sacrificing embankment height or long-term durability.

Produced to PAS 108 specification and derived from waste tyres that would otherwise enter lower-value disposal routes, tyre bale fill combines genuine engineering performance with a strong sustainability case. This guide covers how the material works, where it is applied across UK infrastructure projects, and what recyclers need to demonstrate to supply compliant bales into the civil engineering market.

The Lightweight Fill Problem in Geotechnical Engineering

Building embankments over soft or compressible ground is one of the most common challenges in road, rail, and flood defence construction. Conventional granular fill, placed in a conventional embankment, applies a vertical stress to the soft ground beneath that the ground may not be able to support without significant settlement or instability.

The responses available to the engineer are limited. Soft ground improvement through surcharging, dynamic compaction, or ground treatment adds programme time and cost. Piled foundations beneath the embankment structure add significant cost. Routing around the problem area is often not possible without major realignment.

Lightweight fill materials reduce the net load applied to the soft ground without reducing the embankment height. By substituting a portion of the conventional fill with a material of substantially lower density, the total vertical stress on the subgrade is reduced, settlement is reduced, and stability is improved. PAS 108 tyre bales are one of the established lightweight fill materials used for this purpose, alongside expanded polystyrene (EPS) blocks and lightweight cellular concrete.

The case for tyre bales in this application is strong: they are lower in cost than EPS, more sustainable than virgin materials, and represent a high-value use of waste tyre material that avoids lower-value disposal routes.

Why Tyre Bales Work as Lightweight Fill

The engineering performance of tyre bales as lightweight embankment fill rests on several material properties.

Low bulk density. A PAS 108-compliant tyre bale has a bulk density in the range of 500 to 700 kg/m³. This compares to approximately 1,800 to 2,200 kg/m³ for granular fill. Replacing granular fill with tyre bales in the lower portion of an embankment reduces the vertical stress on the subgrade by up to 70 per cent for the replaced depth. The reduction in load is proportional to the density difference and the depth of replacement.

Compressive stiffness. PAS 108 tyre bales have a defined compressive stiffness that allows engineers to predict how the bale layer will deform under load. This is essential for settlement calculations and for designing the transition from the bale layer to conventional fill above. The stiffness values used in design are derived from laboratory testing of PAS 108-compliant bales.

Free drainage. The void structure within a bale layer drains freely, preventing pore water pressure build-up within the fill that could destabilise the embankment. This is particularly important in embankments constructed over areas with a high water table.

Long-term stability. Tyre rubber is resistant to biological degradation and chemical attack. A tyre bale layer within a properly designed embankment structure maintains its material properties over a design life measured in decades.

Embankment Applications for Tyre Bale Fill

Road and motorway embankments over soft ground. The UK’s transport infrastructure frequently crosses areas of soft alluvial ground, peat deposits, and estuarine sediments that make conventional embankment construction costly. Tyre bale lightweight fill has been used in road embankment construction in the UK and internationally, where these conditions exist.

Railway embankments and level crossings. Railway embankments over soft ground require tight settlement control to maintain track geometry. Lightweight fill reduces subgrade loading and therefore reduces long-term settlement, which is critical for track performance. Tyre bale fill has been evaluated and used in railway embankment applications where the settlement performance requirements can be met by the design.

Flood defence embankments. Flood banks and levees are frequently constructed over soft floodplain soils. Reducing embankment weight through lightweight fill reduces the stress on the weak foundation soils and may allow steeper embankment slopes for the same factor of safety, reducing the footprint of the embankment.

Approach embankments to bridges. The embankment approach to a bridge structure frequently crosses soft ground and must connect to the rigid bridge abutment without differential settlement that would create a step in the road surface. Lightweight fill in the embankment reduces total settlement and can be used with ground improvement at the abutment to manage the differential settlement between the flexible embankment and the rigid structure.

Design Requirements for Tyre Bale Embankment Fill

Designing a tyre bale lightweight fill embankment requires geotechnical engineering input. The following outlines the key design considerations without constituting design guidance.

Subgrade assessment. The bearing capacity, compressibility, and consolidation characteristics of the soft subgrade determine the extent of lightweight fill required and the expected performance of the embankment. Standard geotechnical investigation (boreholes, cone penetration tests, laboratory testing of subgrade samples) provides the necessary data.

Fill geometry. The tyre bale lightweight fill zone is typically placed in the lower portion of the embankment, where its load-reducing effect on the subgrade is greatest. Conventional granular fill is placed above the bale zone, with a transition layer to distribute load evenly across the bale surface.

Settlement analysis. The design calculates the expected settlement under the proposed fill loading and compares it against the tolerable limits. Where settlement is predicted to be within limits with tyre bale fill but not with conventional fill, the case for lightweight fill is clear.

Stability analysis. Slope stability calculations for the embankment use material parameters for both the tyre bale zone and the conventional fill above. The lower density of the bale zone reduces the driving force on the potential failure surface through the embankment, which generally improves the stability factor.

Drainage design. Water entering the bale zone needs a designed drainage path. Lateral drainage through edge drains and outfall pipes is standard. Preventing water from being trapped in the bale zone by impermeable layers above or below is an important design consideration.

PAS 108 Compliance in Embankment Fill Applications

For embankment fill applications, PAS 108 compliance is not a bureaucratic requirement; it is an engineering necessity. The geotechnical design of a lightweight fill embankment uses specific values for bale density, compressive stiffness, and permeability. These values come from test data on PAS 108-compliant bales.

If the bales installed are not compliant, the installed material may have lower density than assumed (which reduces the load-saving benefit), lower stiffness than assumed (which increases settlement above what was calculated), or inconsistent dimensions (which affects how the bale layer behaves as a coherent unit).

Tyre recyclers supplying bales for embankment fill applications need to demonstrate PAS 108 compliance to the project engineer and contractor. This means not just making bales that are roughly right but operating a production and quality management system that generates documented evidence of compliance for each batch supplied.

The MKII Tyre Baler from Gradeall produces PAS 108-compliant bales when operated with the correct tyre pre-processing and loading protocols. For truck tyre bales, the truck tyre sidewall cutter is an essential pre-processing step, and the full tyre recycling equipment range covers all the stages needed for compliant production.

“The civil engineering market expects a consistent, documented product,” says Conor Murphy, Director of Gradeall International. “Recyclers who invest in proper pre-processing and quality monitoring find the embankment fill market is a reliable, high-value outlet for their bale production.”

Comparing Tyre Bale Fill to Other Lightweight Fill Options

Tyre bale fill is one of several lightweight fill options available to engineers. Understanding where it sits relative to alternatives helps recyclers make the case for the material and helps engineers understand when it is the appropriate choice.

Fill Material	Typical Density (kg/m³)	Key Advantage	Key Limitation
Conventional granular fill	1,800 to 2,200	Low cost, widely available	High load on subgrade
PAS 108 tyre bales	500 to 700	Low cost, waste-derived, durable	Limited availability in some regions
Expanded polystyrene (EPS)	15 to 30	Ultra-low density	High cost, petroleum-derived
Lightweight cellular concrete	300 to 800	Consistent properties, rigid	Higher cost than tyre bales
Pulverised fuel ash (PFA)	1,000 to 1,200	Widely available, low cost	Not as lightweight as tyre bales

Tyre bales occupy a useful position in this comparison: significantly lighter than granular fill, much less expensive than EPS, and derived from a waste material that would otherwise require disposal. For many soft ground embankment situations, the combination of low density, low cost, and sustainability credentials makes tyre bales the preferred lightweight fill option.

Contact Gradeall International to discuss the PAS 108 bale production capability for embankment fill supply.

Frequently Asked Questions

Tyre bale embankment fill raises specific questions from engineers, contractors, and recyclers alike. The answers below cover the design, compliance, and practical considerations that come up most often on civil engineering projects.

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