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Switzerland

The penetration tests in the last three years were carried out:

-    50 % by contractors

-    40 % by consulting engineers

8 % by road boards

-    2 % by technical schools.

With regard to this relatively high pro-duction, one should bear in mind that in Switzerland the cost for penetration testing is about 6 to 10 times lower than for core drilling. Therefore eco-nomical considerations are an essential factor in the choice of the testing method although, considering the local soil properties, it would be preferable to drill.

4. Used penetrometers

Table 3 shows the technical data of the penetrometers used in Switzerland. Only the middle weight penetrometers type VAWE is of common usage. Ali other de-vices are represented at best by two identical specimens.

5. Evaluation

The penetration diagrams allow a generał interpretation of the compactness and some conclusions on the lithology, pro-vided a valid geological model exists.

Some of the materiał properties can be estimated by analogy with well-known sediments. The great majority of the persons consulted in this respect are of the opinion that penetrometer tests should only be used in connection with expłoratory drilling or other direct outcrop data, i.e. as a means of inter-polation or extrapolation.

The ground-water table can be measured in some cases after extracting the pe-netrometer-rods. In poorly permeable soils however results of such measure-ments are frequently falsified. It is therefore preferable to install further piezometers in the hole by means of which the ground-water table can be ob-served over a certain period of time.

The data furnished by penetrometer tests could be improved by various devices aiming at extracting samples. The SPT tool is actually also based on this principle. Two principally different extraction tools can be distinguished:

- driven pipes which allow to extract samples "continuously",

- rotation devices permitting the ex-traction of samples at a preselected depth.

With the driven pipę the danger of clogging exists and it is then impos-sible to sample further strata. Such samples are always heavily compressed.

The rotation devices include the risk of taking along materiał of the upper layers.

It is evident that with those samples only the materiał as such - with the necessary reservations regarding their depth - can be defined. On no account soil properties should be determined.

The rod friction of penetrometers can be eliminated or measured separately by using a casing, mud fluid or else by pulling back and re-driving the rods. Morę refined techniques are also used.

6. Trends of development

Slightly morę than half of the ques-tioned firms and institutions, i.e.

33 % of the Technical Schools, 43 % of the Road boards, 68 % of the Consulting Engineers and 73 % of the Drilling Contractors, consider the current dynamie and static penetrometer tests to be sufficient for the actual purpose. A further development would however be welcomed by a large majority. Sugges-tions as to the naturę of this develop-ment vary widely. Three tendencies seems to crystallize:

a)    Rationallzation

The advocates of rationalization wish to uniform the penetrometer tools as we11 as to mechanize them so as to speed up exploratory work.

b)    Improyęment of the methods of Interpretation

The wish has been expressed that by statistical interpretation of all available results, the evaluation of soil properties with penetrometer tests be put on a firm basis. Therefore a comparison of the forecasts, based on penetrometer data, with the actual soil properties should also be madę.

c)    Dęyęlopment of the exploratory tech-nigue

The development of a in-situ determi-