Geotechnical investigations are essential to determine the nature of the soils or to assess seabed conditions for all marine construction and engineering projects.
Sub bottom profiling consist in characterizing the subsurface layers of marine soils
Beyond the mapping of the seabed revealed by bathymetry, marine geological profiling of the underlayers allows us to detect and map the interfaces between the different sedimentary strata or the soft ground / bedrock interface.
The technique used for the sub bottom profiling is based on the principles of seismic reflection. And so if there is a trade-off between resolution and signal penetration, it is in favour of resolution here, with signal penetration limited to a few metres into the soil.
Seismic reflection is the process of characterizing the deeper layers of marine soils
The seismic imaging is a geophysical method of subsurface observation that outperforms sub bottom profiling measurements in terms of penetration depth. It allows to visualize geological structures through the analysis of seismic wave echoes, these echoes being generated by the heterogeneities of the subsoil. The results are then entrusted to the expertise of geotechnicians who interpret the images.
To validate our understanding based on electronic measurements provided by sub bottom profiling or seismic, we also often undertake field studies, such as geotechnical drilling and sediment sampling.
There is a wide variety of techniques for studying the seabed and underlying substrates.
Stratigraphic interpretation of sediment cores (hand corer or vibrocore) or observation of grab samples can punctually complement electronic sub bottom profiling or seismic studies conducted on a much larger scale. Then, laboratory analyses can provide specific information on soil composition and dynamics.
To estimate sediment density or thickness in situ, dynamic penetration techniques such as water-jetting with divers, will be used until the bedrock is reached.
Mud density penetration
An innovative geotechnical system for profiling loose sedimentary layers
The density of a sludge can be an important factor in marine foundation or dredging work. Mud density can affect penetration rate, drilling stability, transport and sedimentation rate, pumping efficiency.
In order to determine the rheological and density conditions of very loose soil layers, we deploy submersibles accelerometer probes. Data acquired from on-board accelerometers, inclinometers and pressure sensors feed a dynamic model that determines the rheological parameters of the intrusive environment (depth, non-drained shear and viscosity).