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Part D - Minimum requirements on site investigations 
Part D: Minimum Requirements on site investigations for cable rou 
tes for the inter-array network and the power cables 
The objective of geophysical and geotechnical survey of cable route corridors is to gain 
sufficient information regarding the characteristics and the geology of the seabed such that 
cables can be installed in the proper manner. The findings of such investigations are used on 
the one hand to optimise a planned cable route corridor whilst taking unknown situations into 
account whilst also establishing a suitable installation method. The findings must therefore 
make it possible to determine the quality of the seabed regarding cable layering and to calcu 
late the expected installation depth for the planned installation method (so-called “Burial 
Assessment”) within each part of the cable route corridor. 
Measurement of the cable route corridor must cover the entire cable corridor. This applies to 
both the horizontal coverage as well as the measurement of vertical sections. It is usually ex 
pedient to separate the measurement into two independent exploration phases which are or 
ganised into one measurement cruise. 
The first phase contains the geophysical measurements so that a linear insight and overview 
of the measured area is gained. During this first measurement cycle, bathymetric measure 
ments shall be carried out with a multi-beam echosounder (MBES), recording of the surface of 
the sea bed shall be carried out with SSS as well as subbottom profiling (e. g. boomers, chirp 
sonar pinger, parametric echosounder) for determining geological units within the profile. It is 
strongly recommended to combine the SSS measurement with metal detection measure 
ments. Detailed requirements of the respective measuring principle can be seen in Table 10. 
The scope of sediment sampling or geotechnical investigations is established on the basis of 
the assessed and interpreted geophysical measurement data. In case of cable route corridor 
measurements previously carried out in the EEZ within the North Sea, the median sampling or 
probing intervals were typically up to 4 km in geologically homogeneous cable corridor sec 
tions, but in more geologically complex cable corridor sections it was typically 0.5 km. It may 
be necessary to go under this interval to clarify complicated geological conditions. 
After assessing and interpreting the geophysical test results, locations are selected for the 
geotechnical and geological sampling based on the knowledge gained, and such locations 
should enable a comprehensive knowledge of the geological conditions to be gained along 
the cable route corridor with regard to the installation of cables. This covers the sampling of 
all geophysical units which are identified and mapped on the basis of the investigation find 
ings with SSS or subbottom profiling measurements. Locations which appear to make geo 
logical interpretations from geophysical measurements more complicated should also be 
sampled. If the geophysical test results show conspicuous and/or unusual seismic reflectors 
then it is strongly recommended that these are investigated with geotechnical methods. This 
is particularly so when e. g. peat, clay lenses, till etc. are expected. For sampling or geotechni 
cal examination of the sediments, vibrocoring equipment, piston and gravity corers, grippers 
as well as cone penetration testing (CPT) can be used. Further details regarding minimum 
requirements can be found in Table 10. 
The results of cable corridor measurements are illustrated in an independent, comprehensive 
report. Alongside a short project description it is important to name the persons involved in 
the project, describe the systems used for gathering data as well as illustrate the measuring 
procedures. Data processing as well as subsequent assessment and interpretation must also 
be explained. Geophysical and geotechnical findings shall be presented separately before a