6 Materials and products

6.1 General

6.1.1 Construction of reinforced fill involves the use of the following major components:

  • fill material;
  • fill reinforcement, and if required;
  • facing system.

All materials and products shall conform to the specifications of the design and with the technical requirements of the suppliers if proprietary systems are used. All materials used shall be mutually compatible.

6.1.2 The source of supply of all materials, fill, reinforcements, facing etc... shall be documented. The source of materials shall not be changed without prior notice.

6.2 Fill materials

6.2.1 General The fill used within the reinforced zone shall be selected to meet the properties required by the design and the project specification. The suitability of a reinforced fill material is dependent on a number of factors that shall be considered when selecting the material:

  • fill workability;
  • function and environment of the structure and long term behaviour;
  • fill layer thickness and maximum particle size;
  • facing technology;
  • vegetation;
  • drainage properties;
  • aggressivity of the fill;
  • fill – reinforcement interaction;
  • fill – internal friction and cohesion;
  • frost susceptibility.

6.2.2 Fill workability The fill workability shall be such that it can be placed and compacted to produce the properties required by the design. The selection of the fill shall take into account the climatic conditions under which the fill will be placed, the compaction plant and local practice and experience. See Annex A for guidance. Any relevant local experience in the construction of unreinforced embankments shall be considered in the fill selection for reinforced fill structures. Any additives used to improve the workability of some fill materials, e.g. lime, cement, shall be considered with regard to construction limitations. i.e. presence of reinforcement layers within the fill, chemical durability. The fill material shall be free from snow and ice. Frost susceptible materials shall not be placed in sub-zero conditions

6.2.3 Function and environment of the structure and long term behaviour Some types of structure have a critical function where post construction settlement is very important. e.g. bridge abutments, walls supporting railway tracks and buildings, or high earth retaining structures etc. In these cases fill material which is easy to compact and which will have subsequent low compressibility shall be selected. (see Annex A for guidance). Where a structure is exposed to flooding and subsequent rapid drawdown the drainage properties of the fill shall be checked for compatibility with the design assumptions. The behaviour of some fine grained soils, shall be considered with regard to the design life, long term performance and function of the reinforced soil structure. Degradable fill materials and friable soils shall not be used unless specific studies are carried out to validate their use. In particular the properties of materials which are susceptible to break down shall be assessed from trial tests, or tests performed on the material after compaction.

6.2.4 Fill layer thickness and maximum particle size The maximum particle size should allow an acceptably even surface to be formed and be compatible with the compacted layer thickness. The maximum particle size can also be a function of the spacing of the layers of reinforcement and, where relevant, of the size of the facing units. The maximum particle size will also be determined by the choice of reinforcement in order to keep the construction damage within the specified design limits. See The compaction equipment used close to the facing of the structure is generally required to be lighter than within the body of the fill (unless specified otherwise by the soil reinforcement system). This may result in thinner compacted layers, to achieve the required fill density. Unsuitable fills such as organic soils, soluble materials and strongly swelling materials shall not be used.

6.2.5 Facing technology The compatibility of compaction induced settlement and post construction settlement with the facing system used shall be considered when the fill is selected. See Annex A and C for guidance.

6.2.6 Vegetation When a vegetative cover on the facing (greened surface) is planned, the fill material placed near the front of the construction shall meet specified requirements for vegetative cover.

6.2.7 Drainage properties When using drainage geosynthetics the drainage and filtration properties of the geosynthetic shall be compatible with the selected fill.

6.2.8 Aggressivity of the fill The electro-chemical, chemical and biological aggressivity of the fill materials shall be considered to ensure that these properties do not have a detrimental effect on the performance of the reinforcement or the facing. The assessment of the electrochemical, chemical or biological suitability of the selected fill in regard to the reinforcements shall be based on previous relevant experience, e.g. established correlation between the soil characteristics and the long term strength losses of the reinforcements. The mechanical aggressivity of the fill materials with regard to the reinforcement or facing shall be considered to assess compatibility with the design assumptions. The assessment of mechanical damage of the reinforcements, or their coatings, caused by the selected backfill during construction shall be based on previous relevant experience where available, or on specific site testing where necessary. This is particularly important where crushed, angular, fill is used.

6.2.9 Fill reinforcement interaction The interaction between the fill and the reinforcement shall be considered to assess compatibility with the design assumptions. The assessment of the fill reinforcement interaction should be based on testing such as shear box or pull-out testing, and/or previous relevant experience where available.

6.2.10 Fill internal friction and cohesion The compatibility of the internal friction and cohesion of the selected fill with the design assumptions shall be considered. The assessment of the internal friction and cohesion of the fill shall be representative of the conditions in which it is used (e.g. density, moisture content, stress level). The assessment of the frictional properties of free draining or granular fill materials (as defined in Annex A for guidance) may be based on previous relevant experience and related to the particle size distribution of the material.

6.2.11 Frost susceptibility Where relevant, non frost susceptible material shall be used to a thickness of the frost depth from any surface exposed to sub-zero temperatures unless an insulating layer is used.

6.2.12 Guidance

Some typical combinations of fill, reinforcement and facing units are considered in Annex A. The electrochemical properties of fills used with metallic reinforcement are considered in Annex B.

EN 14475:2006 Execution of special geotechnical works – Reinforced fill