Testing methods


Probing with a driving rod

The depth of loose clastic rock deposition is determined by light probing using a driving rod. A rod with a defined tip is driven into the soil, and driving progress is measured in relation to the number of hits. The values specified and deposition depth provide additional knowledge, supplementary to exploratory drilling, allowing for development of the first concepts of the type and depth of foundations for the solar panels.

Bore hole detection

Considerations are based on the fact that the parameters determining the load-bearing capacity of the steel piles derive from varying soil structures and their respective different force-bearing capacities. It is, therefore, advisable to pay special attention to the examination of the uppermost 2 to 4 meters of the soil stratum.

With measuring methods taken from the evaluation of founding depths for noise barriers and adapted to the prerequisites of solar power plants, it is possible to reliably calculate the necessary founding depths for all kinds of steel piles, if the following parameters are known:

  • The engineering properties of the ground
  • The dimensions and measurements of the pile
  • Forces and momenta operating on the piles

In addition the vertical application of force and its transmission into the soil have to be examined, drawing on information about the contact stress between piles and surrounding soil. Usually, the pile seat depths calculated from tilting torques and horizontally operating forces are sufficient for the piles to also bear vertically afflicted loads. On rare occasions (very light soils), however, it is necessary to increase the pile seat depth in order to effectively transmit vertical stress.

The evaluation system is computerized and homologated according ZTVE LSW88/03. It is based on the norms for permitted encumbrance to the site (DIN/EN 1054).

Trial pile driving

In these trials a steel pile is usually driven into the soil that needs to be examined. Next, force is applied to the pile horizontally and vertically in order to measure its reaction above the ground (deformation). Finally, the profile is usually pulled from the ground, whereby the strength applied is registered.

This method thus procures information about deformations and the influence of different forces occurring at a recently inserted steel pile. However, it only provides limited information about the actual soil structure and soil-mechanical qualities. Ideally, the trial shows that the pile driven into the ground is, in this condition, able to withstand the stress afflicted by the super-structure, which leads to the conclusion that the same conditions apply after construction of the supporting structures.