Tyre Bales for Slope Failure Repair: Lightweight Remediation Method

By:     Kieran Donnelly

Expert review by:     Conor Murphy

Tyre bales for slope failure repair offer a solution that conventional fill materials often can’t match: enough mass to stabilise a failed slope without overloading the weakened ground beneath it. That combination of low density and structural performance is what makes tyre bale fill particularly well-suited to remediation work, where the ground conditions at the repair location are rarely ideal.

This guide covers the failure mechanisms where tyre bale remediation applies, the engineering principle behind the lightweight counterweight approach, drainage considerations, and the PAS 108 compliance requirements that underpin structural performance. Whether you’re assessing an emergency repair or designing a permanent remediation scheme, the key technical and specification points are set out here.

Why Slope Failures Are Difficult to Repair Conventionally

When a slope fails, the immediate problem is obvious: a mass of soil, rock, or fill has moved from where it should be to where it shouldn’t be. The engineering problem is less obvious but more significant: the slope failed because the driving forces acting on it exceeded the resisting forces. Any repair that simply replaces the failed material in its original position without addressing that fundamental balance of forces will fail again.

Conventional repair approaches address the force imbalance in one of three ways. They increase the resisting forces through structural elements (piles, retaining walls, ground anchors, soil nails). They reduce the driving forces through drainage improvements that lower pore water pressure and increase effective stress. Or they reshape the slope geometry to reduce the gravitational driving force, typically by removing material from the top of the slope (reducing the load that is driving movement) or by placing a counterweight fill at the toe (increasing the mass resisting movement).

The counterweight fill approach is where tyre bales offer a specific advantage over conventional fill materials. A counterweight berm at the toe of a failed slope must be heavy enough to provide the required restraining force, but the weight of the berm itself applies load to the ground beneath it. Where the ground at the slope toe is soft or has been weakened by the failure event, placing a heavy conventional fill berm may either fail to provide adequate restraint (because the berm sinks into the soft ground rather than restraining the slope) or may trigger secondary instability in the toe area.

Tyre bale fill, at one quarter to one third of the density of conventional fill, provides a counterweight berm that applies far less load to the soft toe ground while still providing the mass needed for slope restraint. This lightweight counterweight approach is one of the more elegant applications of tyre bale fill in geotechnical engineering.

Types of Slope Failure Where Tyre Bales Are Applicable

Not all slope failures are the same, and the applicability of tyre bale remediation depends on the failure mechanism.

Rotational slip failures. A rotational slip occurs when a mass of soil slides along a curved failure surface, typically in cohesive soils like clay. The failed mass moves as a relatively coherent block, rotating as it moves, with the toe of the failure pushing up at the slope base. Tyre bale counterweight fill at the toe provides direct resistance to the toe heave that drives the rotational mechanism. This is one of the most common and most appropriate applications for tyre bale slope repair.

Translational failures. A translational failure involves movement of a slope mass along a planar surface, often at the interface between a weak and a stronger stratum. The driving force is primarily gravitational, and the repair typically requires either drainage improvement or structural support. Tyre bale structures can contribute as toe buttresses in translational failure repair, though the design approach differs from rotational failure remediation.

Shallow surface failures and erosion. Shallow surface slips and erosion failures in the upper metres of a slope are often caused by water infiltration and pore pressure increase during heavy rainfall. Tyre bale cover structures and drainage layers can stabilise shallow failure surfaces and prevent re-initiation of shallow slips. The permeable nature of tyre bale fill assists drainage, which addresses one of the primary causes of shallow slope failure.

Embankment slips. Embankment slopes on roads and railways are a common location for slope failure. The fill material in an embankment body may be inadequately compacted, the subgrade beneath the embankment toe may be soft, or drainage through and around the embankment may be inadequate. Tyre bale repair structures at the embankment toe or within the embankment slope are a well-documented repair approach with case study evidence from UK highway and railway embankment repair projects.

The Lightweight Counterweight Approach: Engineering Principle

The counterweight berm approach to slope repair works because adding mass at the toe of a failed slope increases the moment resisting further rotation. In a rotational slip, the failure surface is a roughly circular arc. The failed mass is rotating about a centre point above the top of the slope. Adding a counterweight fill at the toe increases the clockwise (resisting) moment about that centre, opposing the anticlockwise (driving) moment of the failed mass above.

For the counterweight to be effective, it must be placed in the right position relative to the failure geometry, and it must be stable on the ground it is placed on. Here is where the density of the fill material becomes critical.

If the toe area has been weakened by the failure event, or if it is underlain by soft material that was already marginal before the failure, a heavy conventional fill berm may not sit stably on the toe ground. The berm sinks, reduces in effectiveness, and may trigger further instability. A tyre bale berm, at 500 to 700 kg/m³ compared to granular fill at 1,800 to 2,200 kg/m³, applies roughly one third of the load per unit volume to the soft toe ground. The same volume of material provides a similar geometric counterweight effect while applying far less load to the weakened toe.

This is why tyre bale counterweight fills have been used successfully in slope repairs where conventional fill berms had failed or where the geotechnical assessment concluded that conventional fill would overload the toe ground.

Drainage: The Companion to Counterweight Fill

Slope failure in cohesive soils is almost always associated with elevated pore water pressure. Water infiltrating the slope raises pore pressure, which reduces effective stress, which reduces shear strength, which allows failure to occur. Repairing a failed slope without addressing the drainage conditions that contributed to failure means the repair will fail again when the next heavy rainfall event produces similar pore pressure conditions.

Tyre bale fill contributes to drainage improvement in two ways. The permeable nature of a bale fill layer provides a drainage pathway within the repaired slope structure, allowing water to move to the base drain rather than accumulating within the slope body. The counterweight berm at the slope toe, if constructed with a base drainage layer, can also intercept groundwater flowing from the slope above.

The drainage design for a tyre bale slope repair should be deliberate: designed drain positions, specified geotextile filter layers between the soil and bale zones, and base drains with outfall to a suitable receiving point. Drainage in a slope repair is not a detail; it is typically the element of the repair that determines whether it remains stable over time.

Emergency and Temporary Repairs

Tyre bale slope repairs have a practical advantage in emergency situations: the installation is rapid and requires only an excavator and a delivery vehicle. There is no mixing, no formwork, no curing time, and no compaction requirement. Bales are placed by an excavator from the delivery vehicle directly into position. A substantial counterweight berm can be installed in a day of excavator and delivery operations, which is relevant when a failure has blocked a road, threatened a property, or destabilised an infrastructure asset that needs immediate protection.

This rapid installation capability makes tyre bales useful as emergency temporary protection while a longer-term repair is designed and permitted. The temporary bale structure stabilises the situation, prevents further deterioration, and provides time for the proper geotechnical investigation and design that the permanent repair requires.

Temporary bale structures are designed for the temporary loading period rather than the full service life of the slope, which may allow a simpler design approach. They should be clearly identified as temporary in the engineering documentation, with the permanent repair design proceeding on a defined programme.

PAS 108 Compliance for Slope Failure Repair

For structural slope failure repair applications, PAS 108-compliant bales are the required specification. The design of the counterweight berm, toe buttress, or internal drainage structure uses material property values (density, mass, dimensions) that are only valid for bales produced to the standard.

In a slope repair context, the consequence of non-compliance is not just academic. A counterweight berm made from under-mass, under-dense bales provides less gravitational resistance to slope movement than a PAS 108-compliant berm of the same dimensions. If the berm’s mass is insufficient, the factor of safety against re-failure is lower than the design calculation indicates. In an emergency repair context, where the slope has already failed once, this gap between designed and actual performance is particularly consequential.

The MKII Tyre Baler from Gradeall International produces up to 6 PAS 108-compliant bales per hour. Operations with MKII production capability can supply emergency slope repair projects at the delivery rates needed for rapid installation. The pre-processing line, including the tyre rim separator and truck tyre sidewall cutter, ensures consistent input quality for compliant production. See the full tyre recycling equipment range.

“Slope repair is one of the most technically interesting applications for tyre bale fill,” says Conor Murphy, Director of Gradeall International. “The lightweight counterweight principle is elegant engineering. But it only works if the bales are to specification. Under-mass bales in a counterweight berm are not just a compliance issue; they are a structural deficiency.”

Frequently Asked Questions

Slope failure repair raises site-specific questions that standard guidance doesn’t always answer directly. Here are the ones geotechnical engineers and contractors ask most often.

← Back to news