PREMISE

Organising and executing a normal ground investigation does not appear to be a subject worth to be discussed at a professional level. When such work has to be done, however, in remote areas many hundreds of km away from an established base and with the assistance of local untrained workmen a number of quite normal features attain significance which if neglected can jeopardise the whole undertaking as sometimes painful experience has taught.

Weak and factured rocks can be a hazard for the foundation of tall or other heavy structures. In order to use them nevertheless as subbase their properties must be known.

Information regarding this can practically be obtained by tests in situ only. There are many such tests and investigation methods known and commonly acknowledged.

Each of them has its merits and limitations. There is none which alone can provide a comprehensive picture of the rock mass to be investigated, not to mention the effects of discontinuities.

Geophysical investigations for example show integrated features for a comparatively wide area; geomechanical or geohydraulic testa executed in an exploratory hole give very clear and interpretable results; these are, however, relevant only for the immediate vicinity of the hole.

There is practically no way to obtain all desired information. However, the more tests are done the smaller remains the margin of uncertainty. One should therefore attempt to test and verify whatever is possible.

An acceptable compromise must naturally be found between number and variety of tests and the funds which are available.

Too little investigation before planning however has often resulted in high unbudgated costs at a later stage. For major projects a combination of geophysical and mechanical tests should be the norm.

Many tests do not give direct results, they must be interpreted. The value of a ground investigation does naturally not only depend on a careful and professional interpretation because no evaluation of a test can be better than the information on which it is based. The quality of the actually executed work is of utmost importance.

PERSONNEL ENGAGED IN SUBSOIL TESTING

Geophysical or other tests of a high technological standard are usually performed or directly supervised by professional people. Somewhat simpler geomechanical tests on the other hand very often require the handling of heavy and powerful machines or the drilling of holes and the extraction of cores or samples respectively the installation of instruments.

Drilling in collapsing or broken ground for example requires considerable skill and experience.

This skill and experience is normally not available from academics but more so from people used to discharge manual work who, however, usually do not have the intellect, to always understand the purpose and intricacy of specialised tests.

No laboratory test can for example ever produce a meaningful figure for such classical parameters as the modulus of elasticity of a rock body, gravel or sand because the true conditions of the in situ state cannot be reproduced in a laboratory.

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