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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 3


Pre-drilling (b)

PRE-DRILLING (b)   3.3
When penetrating coarse materials, pre-drilling may be used in parts of
the profile if the penetration stops in dense, coarse or stone-rich layers.
Pre-drilling may be used in coarse top layers, sometimes in
combination with casings to avoid collapse of the borehole. In soft or
loose soils, pre-drilling should be used through the crust down to the
groundwater table. The pre-drilled hole should be filled with water if the
pore pressure will be measured by a water-saturated system. If the
groundwater table is located at great depth, the pore pressure system
should be saturated with glycerine or silicone oil.
An example plot is shown in Figure 14. For constructing a concrete
rafter for the foundation of a new building, the settlement of the soft
clay layer between 3 and 7 m below ground level had to be determined.
Therefore a dissipation test was made in the clay layer. Since the
chosen filter location was U1 (face), pre-drilling of the top layer of dense
sand was necessary. A filter location of U2 (shoulder) is less vulnerable,
but sometimes produces a negative pore pressure at the start of
dissipation and therefore the test takes much longer. 

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