Reinforced soil slopes:
Slope surfaces might require stabilisation against either erosion, shallow or deep-seated failure. Depending on the steepness of the slope (strengthened slopes with angles >70o are classified as retaining walls), different geosystems or combinations of geosystems can be used to improve overall stability.
Normally, vegetation provides a natural erosion control system, however it can be difficult to establish on steep slopes in exposed locations particularly if they are north facing. The resistance of the vegetation, particularly during the establishment phase, can be improved by the use of geotextiles to retain the top soil and moisture while being easily penetrated by the plant root systems. For more extreme growing conditions, some types of geosynthetics are available which incorporate a factory-prepared layer of pre-seeded top soil containing slow release fertilisers and water retaining polymers to speed up germination and support growth. Often these systems include a facing geogrid, which will provide a permanent anchor to the vegetation and erosion protection to the soil, and a biodegradable fabric, which will eventually degrade to enable the roots to penetrate the substrate.
Geosystem facings to steepened slopes and retaining walls are commonly connected to geosynthetic/steel reinforcement (or soil nails/anchors) within the body of the slope or the retained ground which acts to improve its overall stability. Horizontal reinforcement such as geotextiles and geogrids can provide a wrap around facing when extra length of the material is wrapped around the slope surface of the reinforced layer and then anchored back into the fill. Alternatively, steel mesh facing can be anchored to the horizontal reinforcement, typically for steeper slopes (up to 70°). Prefabricated steel mesh units, which provide a facing element and a stiff panel that can be pinned in the soil to provide reinforcement and anchorage to the facing element, can also be used, particularly for slope failure repairs.
For walls, i.e. slopes steeper than 70°, structural facing systems and gravity retaining walls are used. These are typically of modular construction and have a significant mass, e.g. precast concrete blocks, concrete or timber interlocking boxes (forming crib walls), gabions filled with durable coarse fill, concrete walls. Anchorage points for horizontal soil reinforcement might be provided on the internal face of the hard facing structure. Specific finishes can be provided to ensure integration in the landscape and “softening” of the surface, e.g. texturing/colouring of the exposed face of concrete blocks, use of local stones for the facing layers of the fill within gabions, crib walls partially filled with top soil to favour growth of vegetation.
Geosystems work with the soil available on site by increasing its stability and limiting its erosion. Use of geosystems results in significant savings in terms of construction time, material cost and waste disposal charges. These are some examples of the savings that can be realised:
The highlighted savings are matched by environmental benefits. Geosystems achieve resource efficiency through reduction of the need for virgin/imported materials and waste minimisation.
This results in savings of natural resources and landfill space. Furthermore, the considerable reduction in transport requirements (for haulage of large quantities of new materials and waste) results in significant avoidance of greenhouse gas emissions.
In many cases the construction period is shortened with environmental benefit in terms of reduced construction noise and less traffic disruption in the adjoining area.
The systems can also provide enhanced conditions for the establishment of vegetation, thus contributing to erosion control and carbon absorption, minimisation of water runoff, increased biodiversity.