Tyre Bales for Coastal Defence: Erosion Protection Using Recycled Tyres

By:     Conor Murphy

Coastal erosion is one of the most persistent and expensive challenges in civil and environmental engineering. The UK has approximately 17,000 kilometres of coastline, and a significant proportion of it is subject to active erosion from wave action, tidal scour, and storm surge. The communities, infrastructure, and agricultural land sitting above eroding coastlines face real and measurable risk.

Conventional coastal defence methods are effective but expensive. Rock armour revetments use large blocks of granite or limestone placed at the base and face of eroding cliffs and embankments to absorb wave energy and protect the toe from undercutting. Concrete sea walls reflect wave energy and provide a hard barrier against further erosion. Sheet pile walls retain soft coastlines at property boundaries. All of these approaches work, but they require significant material, transport, and installation costs that make them difficult to justify for lower-priority stretches of coastline or for temporary protection during longer-term remediation planning.

Tyre bales offer a cost-effective alternative for specific coastal applications where the structural demand is moderate, the budget is limited, and the durability of the material in a marine environment is an advantage rather than a curiosity. Understanding where tyre bale coastal defence works well, and where it doesn’t replace more robust engineered solutions, is the starting point for both engineers specifying coastal protection and tyre recyclers seeking civil engineering supply opportunities.

Why Rubber Works Well in Marine Environments

The marine environment is one of the most aggressive for construction materials. Seawater is chemically reactive, biological fouling affects surfaces within months, the freeze-thaw cycling of splash zones degrades porous materials, and the mechanical action of waves, sand, and shingle abrades surfaces continuously.

Tyre rubber performs well in all of these conditions. Rubber does not corrode, is not susceptible to freeze-thaw degradation, resists the biological action that destroys timber, and has a surface hardness that accepts abrasion without structural compromise. The steel within a tyre bale (bead wire and belt reinforcement) is encased in rubber that protects it from direct saltwater contact for extended periods.

Long-term monitoring of tyre bale coastal installations, including academic research and Environment Agency field assessments, has found that bale structures maintain their physical integrity over periods of more than 15 years in coastal conditions. Surface rubber may show some weathering, but the compressed internal structure of a PAS 108 bale is not significantly affected by marine exposure over the monitoring periods that have been assessed.

This durability profile compares favourably with some conventional materials. Timber revetments require pressure treatment and regular replacement. Some concrete elements in splash zones suffer carbonation and chloride-induced reinforcement corrosion over time. Tyre bales, as a solid rubber and steel composite material, have fewer material degradation mechanisms in the marine environment than many alternatives.

Coastal Applications for Tyre Bale Structures

Cliff toe protection. The toe of an eroding soft cliff is the point where undercutting by wave action initiates slope failure above. A tyre bale revetment placed at the cliff toe absorbs wave energy, prevents undercutting, and protects the face below. Because the bale structure is permeable, it does not reflect wave energy in a way that increases scour adjacent to the structure; wave energy is dissipated within the bale matrix.

This application is particularly appropriate for soft cliffs of glacial till, sand, and clay that erode primarily through undercutting rather than mass failure. The cliff toe protection does not stop erosion of the cliff face above by rainfall and weathering, but it stops the undercutting mechanism that causes sudden collapse and allows a more gradual managed retreat of the upper cliff face.

Shoreline revetments on estuaries and river mouths. The lower energy environment of an estuary or river mouth, where wave action is less severe than an open coast, is well-suited to tyre bale revetment structures. Agricultural land boundaries, access track embankments, and settlement protection berms along estuaries and tidal rivers are common applications. The bale structure sits at the water’s edge, absorbs tidal and wake-generated wave energy, and protects the bank face from erosion.

Temporary coastal protection. Where a coastal structure is awaiting permanent protection works or where the budget for permanent works is not yet secured, a tyre bale revetment provides temporary protection against further erosion. The temporary protection gives time for funding to be secured or for a permanent design to be developed without the site deteriorating further in the meantime.

Beach access track stabilisation. Coastal access tracks that cross beach material and dune systems are frequently subject to erosion and surface degradation. Tyre bale foundations beneath these tracks provide load distribution, drainage, and resistance to the soft ground conditions of beach and dune material.

Construction of Tyre Bale Coastal Structures

Tyre bale coastal revetments are typically constructed in a staggered course arrangement, similar to the approach used in slope stabilisation structures. The staggered bond between courses prevents a continuous vertical joint through the structure, which would be a weakness in the face of wave loading.

Foundation preparation. The base of the revetment is prepared by minor excavation or profiling to create a level seating for the first bale course. Where the beach or cliff toe is subject to scour, a rock or geotextile apron may be placed in front of the bale toe to prevent undermining.

First course placement. The foundation course is the most critical. Time taken to ensure this course is level, well-seated, and aligned correctly pays dividends in the stability and performance of the whole structure. Bales are placed by excavator, typically directly from the delivery flatbed.

Successive courses. Each course is staggered by half a bale length relative to the course below, creating the interlocking bond arrangement. Course heights are typically limited by the reach and stability of the placing excavator.

Tie connections. In structures subject to wave loading, adjacent bales within each course and between courses are often connected using high-tensile wire or strapping threaded through the bale tie wire loops. These connections prevent individual bale displacement under wave impact without requiring a rigid structure that would reflect wave energy.

Facing and surcharge. Exposed bale faces in amenity areas are sometimes faced with beach-harvested material or geotextile to create a more natural appearance. In less visible locations, the bale face is left exposed. Some installations allow vegetation to establish on the bale structure face over time, which improves the appearance and provides additional surface protection.

PAS 108 Compliance for Coastal Applications

For structural coastal protection applications, PAS 108-compliant bales are the appropriate specification for the same reason they are required in all structural civil engineering uses: the design of the coastal structure uses material property values (density, dimensions, mass) that are only valid for bales produced to the standard.

In coastal applications, the most critical PAS 108 requirements are mass and dimensional consistency. Individual bale stability against wave loading depends on bale mass: a heavier bale requires more force to displace. Dimensional consistency ensures bales interlock and stack predictably, creating a structure with the geometry the design assumes.

Under-mass or under-dense bales in a coastal revetment are more susceptible to displacement by wave action than specification bales. Over time, displaced bales create gaps in the revetment face that allow wave energy to penetrate the structure and undercut the cliff or bank behind. Maintaining PAS 108 compliance throughout the supply is not a bureaucratic requirement for coastal applications; it is directly related to the structure’s ability to remain intact under the wave loading it will experience.

The MKII Tyre Baler from Gradeall produces up to 6 PAS 108-compliant bales per hour. For truck tyre bales, sidewall cutting with the truck tyre sidewall cutter before baling ensures consistent density. For the full pre-processing line, see the tyre recycling equipment range. Gradeall International is based in Dungannon, Northern Ireland, with equipment operating in over 100 countries.

Environmental Consent and Regulatory Context

Coastal construction of any type requires engagement with the relevant regulatory authorities. In England, works below the mean high water mark require consent from the Marine Management Organisation under the Marine and Coastal Access Act 2009. Works affecting a watercourse or coastal floodplain typically require Environment Agency flood risk activity consent. In Scotland, Wales, and Northern Ireland, equivalent bodies have jurisdiction.

For tyre bale coastal structures, the environmental assessment requirement focuses on two areas: leachate risk from the tyre rubber in the marine environment, and the physical impact on coastal processes (sediment transport, habitat). The leachate risk question is addressed by reference to published research on rubber behaviour in marine environments, which indicates low risk for properly installed structures. The coastal processes question requires site-specific assessment by a coastal engineer or geomorphologist familiar with the site’s sediment dynamics.

Contact Gradeall International for guidance on PAS 108 bale specification for coastal defence supply.

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