Geotechnical drilling

Marine geotechnical drilling and sampling: An overview

In marine construction, a wide range of different foundations and anchoring or mooring systems exists. Whether a monopile for an offshore wind turbine or an anchor for a floating substation, the optimal solution depends on the ground conditions.  

After a desk study of the proposed project area, contractors collect more detailed information with a site investigation. A site investigation typically includes a geophysical survey and a geotechnical survey.  

First, the geophysical survey offers broad, indirect insights that guide where and how to conduct geotechnical investigations. Then, the geotechnical survey delivers the precise, hands-on data needed for final engineering decisions.  

What is geotechnical drilling?

The geotechnical survey involves using specialised machinery and different types of drills and drilling techniques to collect samples of soil and rock from the seabed. These cores give engineers a detailed understanding of the sediment’s characteristics, such as its composition, strength and stability.

What does a geotechnical report tell you?

In essence, geotechnical drilling and sampling provides the critical data needed to build safely, efficiently and sustainably. 

• Identify subsurface conditions: Core samples reveal soil types, sediment layers and rock formations, enabling engineers to customise foundation designs and installation methods. 
• Enhance structural integrity: Comprehensive geotechnical data helps engineers design offshore structures such as wind turbine foundations, oil and gas platforms or bridges for maximum stability and resilience. 
• Reduce risk and uncertainty: Early and accurate site data helps minimise costly surprises during construction and operation. Often, changing designs once the project has begun is either impossible or extremely expensive. 

• Meet regulatory requirements: Many jurisdictions require thorough geotechnical investigations before issuing permits for offshore projects.   

Why marine geotechnical drilling matters

The information from core samples helps determine the most viable and cost-effective foundation design for the project. For example, different sediment types — such as clay, mudstone or chalk — have distinct load-bearing properties. The more designers know about the seabed, the better they can strike the balance between durability and installation costs. 

Accurate site investigation is crucial to avoid overlooking potential issues in the seabed’s composition because undetected problems can significantly escalate project costs. In extreme cases, when a project is already well underway, the ramifications of unexpected issues can be two or three times the planned total project cost.  

Challenges of offering geotechnical drilling services

Cores collected during geotechnical drilling operations represent a considerable investment of time and money. Unplanned downtime often increases the costs of obtaining these cores because marine geotechnical surveys face several key challenges, including: 

• Vessel heave and stability: Constant movement from waves and currents makes it harder to maintain rig stability, retrieve undisturbed samples and precisely control drilling operations. 
• Tool handling and tripping pipe safety: Managing heavy equipment and long drill strings at sea increases the risk of accidents, making robust health and safety protocols essential. 
• Complex logistics: Transporting specialised equipment to remote offshore locations is expensive, time-consuming and requires careful planning.
• Limited visibility: Operators must rely on remote sensing and subsea cameras, as direct observation of underwater drilling conditions is not possible. 

By recognising these challenges and employing the right equipment and engineering solutions, marine geotechnical teams can ensure quality data collection and successful marine construction projects. Partnering with a marine engineering specialist can help. At MintMech, we recognise the need for precision, reliability and a deep understanding of the challenges of working offshore.  

Our team of experienced engineers has a proven track record of delivering tailored support for a wide range of offshore projects. For information on how we can customise support to align with your project’s requirements, schedule and regulatory landscape, get in touch for a free consultation.