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Part C - Minimum Requirements on geotechnical investigations 
Sampling and the required quantities to be sampled should be planned and carried out re 
garding the planned laboratory tests with the necessary testing technology on the one hand 
and regarding the composition and the degree of homogeneity of the soil on the other hand. 
A sample diameter of D = 100 mm is recommended for soil mechanical laboratory tests on 
homogeneous cohesive sediment samples and for rock mechanical laboratory tests on solid 
rock samples. 
Standard values for sample diameters and sample lengths for loose and solid rock 
• for a drilling process which steadily obtains core soil and rock samples are: D = 100 mm, 
L = 1000 mm 
• when taking soil samples with a thin or thick-walled sampling device from the bottom of a 
borehole in accordance with DIN EN 22475-1: D = 114 mm, L = approx. 250 mm 
• when taking pressure and pile core samples from the bottom of a borehole whilst using spe 
cific sampling technology meant for offshore use: D = 67 mm, and with particularly densely 
packed soils also D = 46 mm. 
Further requirements can be found in DIN EN ISO 22475-1. 
The geotechnical expert shall decide, taking the requirements of DIN EN ISO 22475-1 into 
consideration, on whether the soil or rock samples are treated, transported and stored for 
laboratory analysis or whether preliminary material testing is to be carried out on board the 
ship or the jack-up rig. 
Representative sediment samples for subsequent inspections or additional laboratory tests 
must be stored for at least 5 years after sampling takes place. Storage must be protected 
from the weather and remain cool and frost-free. Spot samples in sample containers and core 
probes in core boxes and liners must be stored in such a manner that mechanical soil and 
rock properties of the samples remain unchanged. 
2.3 Investigation steps 
2.3.1 Preliminary geotechnical investigation 
In the course of preliminary investigations of the wind farm area (Step 3, see Table 1, Sec 
tion A), at least 10% of all planned turbine sites are subjected to a geotechnical survey and 
investigation whilst taking the following aspects into consideration. Different regulations are 
illustrated for preliminary geotechnical investigation of offshore stations in Part C, sec 
tion 2.3.3. 
The location of soil investigation is determined by the geotechnical expert and is based on the 
findings of geological survey whilst taking geological structures into consideration and also 
being representative of the area of the construction site. 
The type of investigation method (drilling, cone penetration testing or if necessary a combina 
tion of drilling and cone penetration testing) is to be decided upon by the geotechnical expert 
whilst taking the expected soil conditions especially those based on the findings of geological 
survey as well as the planned foundation type. 
In predominantly sandy subsoil layers such as e. g. in many project areas in the German North 
Sea, cone penetration testing should be carried out to find out the bulk density in all sites 
where the preliminary investigation takes place. It must also be ensured that representative 
sediment samples are obtained from a sufficient number of boreholes.