Part C - Minimum Requirements on geotechnical investigations 
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In many project areas within the German Baltic Sea which have a predominantly cohesive subsoil 
layers as well as soils similar to solid rock (e.g. chalk), boreholes are necessary to obtain repre 
sentative sediment samples at all sites within the course of preliminary exploration. The need for 
cone penetration testing is determined by the geotechnical expert on a case-by-case basis. 
The exploration depth of borings and cone penetration tests shall be sufficient to allow pos 
sible foundation types to be assessed within the framework of preliminary design planning. 
Therefore, the investigation depth has to be determined by the geotechnical expert, in co-or 
dination with the design engineer. 
It is recommended that the survey concept is agreed upon with the certifying body within the 
meaning of the Standard Design. 
2.3.2 Main geotechnical investigation 
In the course of main geotechnical investigations (step 5, Part A, Table 1), at least one site in 
vestigation has to be carried out at each turbine site. This may be sufficient with homogene 
ous soil conditions. However, when soil conditions are inhomogeneous or otherwise unfa 
vourable, or in case of tripod, jacket or gravity foundations, a larger number of site investigations 
is normally required for execution planning. The geotechnical expert shall decide in this case. 
The investigation method to be used (drilling, cone penetration or a combination of both) shall 
be determined by the geotechnical expert taking into account the expected soil strata, the 
results of preliminary investigation, and the foundation type. 
Different regulations are illustrated for main geotechnical investigation of offshore stations in 
Part C, section 2.3.3. 
The investigation depth, as a minimum, shall meet the requirements of design planning and 
thus has to be determined by the geotechnical expert, in co-ordination with the design engi 
neer (see chapter 2.3.1). 
2.3.3 Special regulations for offshore stations 
Usually a minimum of four ground investigations for foundation structures are carried out in 
the corner areas of the structure or in all sites of the foundation elements (piles). The respec 
tive distance between individual investigations and the assigned foundation element (pile) 
must be no more than 30 m for large foundation structures, otherwise additional explorations 
must be arranged. 
For offshore stations (as well as for external converter stations as well as substations or other 
stations within the wind farm) the steps for preliminary and main investigation (development and 
construction phase - see Part A, Section 2) can be formally summarised. The associated reports 
should be submitted to the Federal Maritime and Hydrographic Agency in a certified manner for 
the second release at the latest. If necessary, submission of the first release is also possible. 
Also, the guidelines apply in accordance with Sections 2.3.1 and 2.3.2. 
2.3.4 Supplementary investigations 
Supplementary investigations or field tests such as e. g. pile driving or pile load tests may be 
come necessary as a result of the design work, the geotechnical verification of the initial de 
sign or the invitation to tender, especially with separate proposals. The same principles as for 
site investigations apply here. 
The findings of the geotechnical investigation should be compared with the findings of the 
geophysical survey, and the geophysical measurements should be subsequently interpreted 
on the basis of the geotechnical investigation.