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Published By Lankelma

Lankelma is the foremost contractor for onshore in-situ soil testing in the UK. An acknowledged specialist in CPT, Lankelma also offers a worldwide consultancy and training service.

A.P. van den Berg develops, designs and manufactures geotechnical and environmental soil investigation equipment for onshore and offshore applications. Specialists in CPT systems and equipment.


Gardline Geosciences offers worldwide marine geotechnics, in-house consutancy and services with marine investigations ranging from nearshore to full ocean depth (down to 3000m).

About the Author

Hans Brouwer studied civil engineering at Delft University in The Netherlands. He has worked as a part-time lecturer at Amsterdam Polytechnic and was senior partner in a structural engineering consultancy. He has written a standard textbook in Dutch about the design of building foundations. He now lives in England where he writes technical textbooks in English, hopefully to reach a bigger readership.

Chapter 10

Offshore testing


          INTRODUCTION   10.1 
Further offshore, water depths are too great for jack-ups so vessels are
used. Two types of geotechnical investigation can be performed with a
vessel-based system: a seabed system or a drilling based system.
For static operations such as drilling and down-hole CPTs, vessels with
the means to stay stationary have to be used. This can be achieved by
using mooring systems, or (more expensively) vessels with dynamic
positioning capabilities.
Drill ships need a moon-pool (a hole in the ship’s deck) so that the work
can be carried out safely and efficiently. Occasionally a drill system will
be mounted on a cantilever platform over the side. A heave
compensation system is needed as well as a seabed reaction frame
(clamped around the drill pipe) for the CPTs. This heavy compensation
system is designed to keep the drill stationary relative to the seabed,
enabling the vessel to move up and down with the swell. These systems
allow drilling operations to be performed offshore and samples to be
recovered, and down-hole CPT tests to be performed.
    However, smaller seabed systems can be deployed from larger types of vessels. In essence only a barge or vessel with a suitable crane or A-frame is necessary. The selected vessel must have the ability to remain on station throughout the test either by anchoring or more commonly holding station using its bow and stern thrusters. Figure 89 shows a typical portal frame arrangement deploying a seabed resistivity system. 

The methods of performing seabed investigations are detailed over the
following pages. These can vary from the simplest form of grab
sampling to new high quality sampling and CPT testing techniques.
The following marine site investigation tools will be described.

  • Seabed CPT systems
  • Seabed soil samplers
  • Seabed resistivity systems. 


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