Offshore Site Investigation

Offshore site investigations are critical in understanding the geotechnical and geological properties of the seabed, which is essential for the safe and efficient design of marine infrastructure. Whether it’s for oil and gas exploration, renewable energy projects, or underwater construction, acquiring reliable samples and precise geotechnical data is a cornerstone of any successful offshore project. EEL offers worldwide hire, delivery, and support for all required equipment to complete an offshore survey. Below, we will explore the features and requirements of this equipment in service.

Reliable Samples & Precise Geotechnical Data

Accurate data collection is the foundation of any offshore site investigation. To ensure the safety and stability of marine structures such as wind turbines, pipelines, or oil rigs, engineers rely on high-quality seabed samples. Offshore investigations use specialized equipment that must operate in challenging environments, where variables like high pressure, currents, and unstable sediments come into play.

Among the essential tools for collecting seabed samples are:

• • Seabed corers: These devices penetrate the seabed to extract cylindrical core samples, providing a vertical profile of sediment layers. Vibrocorers, piston corers, and gravity corers are commonly used for this purpose. Each type is selected based on the sediment composition, water depth, and data requirements.

• • Grab samplers: For surface sediment analysis, grab samplers like the Van Veen or box grab are deployed. These tools retrieve bulk samples of the top layers of the seabed for sedimentological analysis.

Collecting reliable samples is vital for determining soil composition, stratigraphy, and the mechanical properties that impact construction. The precision of this data ensures informed design decisions, preventing costly errors during construction and long-term operations.

Sampling & In-situ Testing Capabilities

Beyond sample retrieval, in-situ testing plays a crucial role in offshore site investigations, providing data on soil behaviour under real conditions. In-situ tests offer continuous or point-specific measurements of soil properties like strength, permeability, and deformation, which are critical for understanding the seabed’s stability.

Some of the most widely used in-situ testing methods include:

• • Cone Penetration Testing (CPT): The CPT system, equipped with a cone-tipped probe, is pushed into the seabed at a constant rate to measure the soil’s resistance. This method provides direct readings of parameters like tip resistance, sleeve friction, and pore pressure, offering insight into soil strength and stratigraphy.

• • Seismic CPT: An advanced variation of CPT, seismic CPT involves measuring the propagation speed of seismic waves through the soil, which helps assess the shear strength and density of sediment layers.

• • Pressuremeter Testing (PMT): In this test, an inflatable probe is expanded in the borehole to determine the soil’s pressure-deformation response. This data is used to assess the compressibility and shear strength of the soil.

• • Dilatometer Test (DMT): The DMT uses a blade with a flat circular probe inserted into the seabed. The pressure required to lift a membrane on the probe is measured, providing information on soil stiffness and consolidation characteristics.

These techniques are invaluable in environments where sediment characteristics vary significantly, such as in deepwater or dynamic coastal areas. Combined with sampling, they offer a comprehensive understanding of soil properties across different depths and regions, allowing for the development of robust engineering solutions.

Data Processing & Interpretation

The success of any offshore site investigation lies not only in the collection of data but also in its processing and interpretation. Given the large volumes of geotechnical data obtained from offshore investigations, advanced software tools are employed to organize, analyse, and interpret the findings effectively.

• • Data Analysis Software: Tools such as geotechnical software platforms and Geographic Information Systems (GIS) help compile data from different sources, including geophysical surveys, CPT data, and sample analysis results. These platforms can generate 2D and 3D models of the seabed, highlighting variations in soil layers, subsurface structures, and potential hazards.

• • Subsurface Mapping: Using the geotechnical data collected, detailed subsurface maps are created, which reveal the stratigraphy and mechanical properties of the seabed. This mapping is essential for identifying features such as boulders, faults, or gas pockets that may pose risks to offshore operations.

• • Geotechnical Interpretation: Skilled geotechnical engineers analyse the processed data to assess risks and provide recommendations. This stage involves evaluating soil stability, bearing capacity, liquefaction potential, and other factors critical to the design and installation of marine structures.

Incorporating these methods ensures that the data is not only accurate but also actionable. Well-interpreted data can significantly reduce project risks, optimize foundation designs, and extend the operational life of offshore installations.

Offshore site investigations are a complex but essential part of marine development, involving the integration of specialized equipment, robust testing methods, and precise data interpretation. With the right tools and expertise, engineers can confidently design and construct offshore structures that are safe, stable, and built to withstand the challenging conditions of the marine environment.