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Penetration testing in Switzerland    esopt

P. Crettaz & H. Zeindler    State-of-the-art report

A brief abstract of the surface geology in Switzerland is presented. On this background the results of an inquiry, comprising 64 answers, show the actual and futurę use and possibilities of pe-netrometer testing.

While dynamie penetrometers are mainly in use now, a tendency towards morę so-phisticated static devices is being no-ted: (Pile model etc.)

Penetrometer tests may give valuable data for correlation and extrapolation provided they are combined with geolo-gical and geotechnical Information (out-crops, core drilling laboratory results etc.)

1. Geological synopsis

Switzerland can be subdivided geologi-cally into three main parts:

-    the Jura,

-    the Central Basin lying somewhat lower,

-    the Alps with a northerly hi11 rangę,

However, these three parts are closely connected as well stratigraphically as tectonically; they virtually belong to the alpine body.

The poorly Consolidated surface for-mations which are of particular interest to us belong to the Quarternary and com-prise (see Geotechnical Map of Switzerland 1 : 200 000):

-    sands, silts, clays often with boulder (so-called ground moralne) or with de-bris and blocks (so-called surface moralne),

-    decalcified silts and clays (so-called weathered clays),

-    argillaceous silts, clays including sand beds, gravel or peat beds, lacu-strine clay formations and slope wash,

-    gravels and sands, clean deposits (so-called "Schotter") often cemented,

-    gravels and sands from recent water-courses,

-    angular pebbles, coarse to fine debris occurring as slide and slope detritus,

-    larger peat formations.

These various rock sequences are being

found all over Switzerland. Morę or less cohesive slope detritus with boul-ders predominate on the slopes of the Jura, the corresponding sediments pre-vail in the valleys.

The surface formations in the Central Basin are similar to those in the pre-alpine valleys, but regions with fill-up series which are often covered with fluviatile deposits are larger.

Very coarse debris, fluviatile gravels and sand as well as lakę deposits occur in the alpine valleys. These rock mat-erials are all mixed together in recent as well as in glacial sequences. In the valleys of the Pre-Alps lacustrine and fluviatile deposits (recent-glacial-in-terglacial) prevail whereas their high-er parts are covered with moraineand weathered soils.

2. Some basie remarks regardlng the use of penetrometers

The soil properties of the above men-tioned ąuarternary series change funda-mentally over short distances, accor-ding to their origin and their sedimen-tation, both in the horizontal and ver-tical direction.

When using penetrometers, one should re-alize that:

a)    The penetration tool allows, at rela-tively modest expense, a quick check-ing of the compactness and uniformi-ty of the soils and consequently pro-vides valuable Information about its composition•

b)    A precise relationship between penetration resistance and soil charac-teristics cannot be established be-cause of the variety and heterogeni-ty of the sedimentary sequences.

Their direct determination is there-fore impossible - with very few ex-ceptions.

Static penetration devices can seldom be used sińce the sediment sequences con-tain practically always harder inter-calated layers. For the same reason, preference is given to heavy penetrometers. On the other hand, heavy equipment must often be excluded a priori because of bad accessibility. Therefore the use of the medium-sized penetrometer accor-ding to DIN standards has been adopted. The latter, inspired by a Swedish model, has been introduced as a compromise by the Institute of Foundation and Soil Mechanics (IGB), formerly the VAWE.