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Compressible Inclusion

In general a compressible inclusion is any material that is significantly more compressible, at least in one direction, than other materials that it is in contact with. Using a compressible inclusion can result in significant reduction in earth pressures under static and dynamic loading. A compressible inclusion can also be used to accommodate ground or structure movement.

Using a compressible inclusion can be cost effective for both new construction as well as rehabilitating or upgrading existing structures. Geotechnical applications for a compressible inclusion include behind earth retaining structures, around foundation elements, and above pipes, culverts and tunnels. Because the inclusion is the most compressible component of the structure-inclusion - ground system, the inclusion will deform more readily than the other system components under applied stress or displacement.

This selective compression of the inclusion can result in a variety of benefits. Most often, this is a load on the structure that is significantly less than if no inclusion were present. In many cases use of a compressible inclusion is a more cost effective alternative than designing the structure to withstand the greater load.

Selection of Compressible Inclusion Materials

RMAX GeoFoam® is an excellent material for compressible inclusions because it has predictable and controllable stress strain behaviour and maintains predictable behavior when wet.

It also does not decompose when wet; some other materials such as hay bales and cardboard do decompose in this situation. For compressible inclusion applications, stiffness of the GeoFoam in the primary displacement direction is the most relevant property.

Compressible Inclusion Applications

For compressible inclusion applications, the lowest density EPS is generally desirable as the Initial Young’s Modulus and Compressive Strength (typically defined as compressive stress at 10% strain) both decrease with decreasing density. Experience indicates that the minimum EPS density that strikes a balance between stiffness and durability is approximately 12 kg/m3.

Examples of the use of Compressible Inclusions:

  1. Volume change of earth materials.
    There are several situations where volume changes of soil and rock are caused by physical changes within the material. Examples include:
    • swelling and freezing soils, and
    • rocks that swell due to water absorption, mineral changes, or release of tectonic stresses.

When such materials are adjacent to earth retaining structures, especially rigid, non-yielding ones, the lateral pressure generated by the expanding soil or rock can be significant.

The use of a compressible inclusion between the structure and ground can allow the soil or rock to deform laterally while transmitting only a fraction of the stress to the structure. The use of a compressible inclusion to reduce lateral pressures due to swelling soils is particularly attractive given the extensive occurrence of such soils worldwide.

Designing to eliminate, or at least minimize, the effects of such soils, or remediating structural damage they cause, represents a significant cost in many areas. 

Typical Retaining Wall

Typical retaining wall

Typical Retaining Wall

Retaining wall with compressable inclusion

Typical bridge abutment

Lightweight EPS bridge abutment

Internal bridge shuttering

Weight reduction application

Compressable Inclusions

Elevation changes/stadium seating

Noise barriers and walls

Accommodating structure movement.

There are situations where lateral displacement of an earth retaining structure is caused by external factors other than lateral earth pressures. This occurs primarily in rigid, indeterminate structures subjected to temperature- induced strain.

In some cases, this movement can result in lateral earth pressures on the retaining structure in excess of at rest and approaching the passive state. The traditional approach is to design the structure for these elevated potential earth pressures. In some cases, it is necessary to repair structures that are distressed because of inadequate design.

A more cost effective alternative for both new and remedial construction may be to use a compressible inclusion to allow the structure to move yet transmit a reduced magnitude of displacement to the retained soil.

RMAX GeoFoam® is cost effective and particularly well suited for both earth volume changes and structural movement.