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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 9

Near-shore marine testing

Overwater cantilever frames

 For cone penetration tests in harbours, often a cantilever frame can be
used. This is much cheaper than deploying a platform. The tests must
be carried out using a casing (Figure 86); without a casing, the 36 mm
thrust rods for a CPT will buckle.

Figure 86
The standard casing is 55 mm diameter which provides additional
lateral support to the CPT rods. Generally these 55 mm casings are
themselves supported by a drill casing to resist the lateral forces of
tide, current etc.
It is essential that, prior to a marine investigation, the requirements are
properly assessed. If the purpose of the investigation is to assess the
near-surface sediments of the harbour or other bed, then typically the
tests should be performed in two parts. The first test is performed from
the bed surface with no support casing to enable the surface deposits
to be tested without disturbance. The thrust is very limited on this first
push due to the lateral stability of the rods. On completion of the first
push the casing can be set to a depth in the initially tested material;
then once properly supported, the full thrust of the equipment can be
used to advance the test to the required depth.
Figure 87 (below) shows a plot of a typical CPT test in a

     Figure 87 

 On the left side of the chart (Figure 87), the plot shows the cone
resistance and the sleeve friction. In the middle is the friction ratio
which allows the soil type to be estimated, as shown on the right. The
harbour bed consists of a soft clay layer of approximately 6 m
overlaying silty sand (possibly highly weathered mudstone).
The cantilever platform can be used as a standalone item of
equipment  (Figure 86) or can be mounted on a variety of land-based
or marine equipment thereby providing a very flexible, cost effective
alternative to conventional equipment. 

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