Technical requirements and tests for wind farm roads and hardstands

Two readers asked me how to assess the quality of the civil works in a wind farm.

This is a very broad topic and it requires some previous knowledge in geotechnics and road construction.

However, I think that someone might found useful an introductory article with some of the requirements that I would recommend to include in the technical specifications and test during construction.

The objective of these requirements and tests is to confirm that the materials used are appropriate and that the works have been properly executed.

As the readers of this website are from different geographic areas, I will not suggest a specific national or international norm such as ASTM, AASHTO, UNE, etc.

Finally, I also intentionally did not specify the value that I consider appropriate for each parameter.

However, if you need support to find an adequate standard or to define a specific value, please feel free to contact me.

For the embankments, I would recommend to define:

  • Maximum grain size. This requirement will avoid the presence of rock and boulders in the wearing surface of the road.
  • Appropriate gradation by sieve analysis (that is, the “granulometry” or particle size distribution). This requirement will ensure an appropriate interlocking between the particles and it is linked to almost all other property (e.g. stiffness, fatigue resistance, permeability, etc.).
  • Atterberg limits (Liquid limit and Plasticity index). You do not want to use plastic material behaving like clay.
  • Low organic matter and soluble salts content. This requirement will insure that only appropriate materials are used in the construction of the embankment.
  • Very low swelling or collapse potential.

The material should be properly compacted. Compaction grade is defined by the percentage achieved compared to the “optimum Proctor value”.

You also want a low deformability. This is usually defined the “Strain modulus” (or “Ev1” and “Ev2”) – basically the deformation of the material under two load cycles as resulting from a Plate Load Test.

I would also recommend defining a minimum CBR (“California bearing ratio”) value for the top and the core of the embankment.

If possible it is always a good idea to build a test section of the road, for a full-scale trial of the construction procedure. It can also help to determine the most appropriate compaction moisture – the actual value could be different from the value given by the laboratory test.

Graded aggregate is the material used in the upper layers of the internal roads.

It is made of well-graded crushed stones. The typology of arid to use and its granulometry depends on the local availability of materials.

In addition to the parameters defined for the embankments I would recommend to specify:

  • Sand equivalent (because you want as little clay as possible).
  • Loss by abrasion (because you want to use for the wearing course a material that can last for several years, ideally more than 20).

It is also advisable to define the maximum difference between the actual roads finished surface compared to the theoretical surface defined in the project.

Finally, compaction must be verified. Again, the standard option is the plate bearing test.