Geotechnical site investigations are conducted following the geophysical survey to use the information obtained to target soil and rock strata boundaries, engineering properties and specific sea floor features.   Boreholes and CPTs are carried out to investigate the physical characteristics of the sea bed. Surface push CPTs are also used as a rapid method to gather sea bed soil stratigraphy. Cable routes are typically investigated using vibro-cores and CPTs.

Offshore laboratories are used to obtain basic soil parameters and samples are taken there for detailed testing once they have been collected. Often soil dynamics tests are performed to monitor the soil behaviour under the constant dynamic loading on the foundation by the wind, waves and current.