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State-of-the-art report

Penetration testing in Czechoslovakia

K. Drozd & M. Svasta

The development of methods using penetration principles in the geotechnical site investigations has been directly influenced by the geomorphological and geological conditiona of the Czechoslo-vak country. Czechoslovakia, in contrast to most other countries, is charakter-ized by a great variety of country types alternating in short diatances. About four fifths of the total area is a rolling countryaide with valleys of the upper or middle courses of rivers origi-nating in Czechoslovakia. Therefore bed-rock materiale are mostly quite near the earth surface and the river deposits, owing to short transportation, are main-ly cooposed of coarse materiał. Only in some broad valleys in the areas where the rivers leave Czechoslovakia or in local tectonic basins filled with Terti-ary or Ouaternary deposits is the fine materiał suitable for penetration testing. But as these lowlands represent the most fertile areas, the industrial or dwelling centres have avoided them for a long time so that no need for special site investigations was necessary. Only within the last decade has a rapid con-structional industry overtaken even these parts of the country.

Map on figurę 1 shows the areas where penetration testing can be used but even there it can be omitted owing to the testing on undisturbed soil samples.

Tertiary deposits are composed mainly of clays, silts, sands with interbeds of gravels. These older deposits are covered with eolian deposits - loess, slope deposits - clayey, clayey - sandy and sandy - loamy soils and loess loams, fluvial deposits - sandy gravels, sands, silts, sandy to clayey flood soils, and glaciofluvial and glaciolacustrine deposits - gravel sands, sands, sandy -loams and clays. Areas of sand deposits piled up by the wind in thicknesses from 2 to 10 metres or sandy lakę or river deposits where other testing

methods failed are concentrated in re-latively smali isles or form narrow and thin strips.

At first there was an intention to apply penetration methods in order to minimize other morę costly methods as for example, in situ piąte loading tests and minimize lsboratory testing on undisturbed soil samples in case the blow-count during sampling would be identi-cal. It was also intended to elucidate the stratification of soil layers be-tween boreholes.

The introduction of penetration methods in Czecho8lovakia is connected with the CzechosloYak expert ArnoSt Dvofrśk from the National Corporation Stavebni geologie, Praha, who has applied the well known Standard Penetration Tests soon after the Second World War. Neverthe-less, specific conditiona of drilling methods used in Czechoslovakia led to substituting the SPT spoon samplers by heavier spoon samplers which enable sampling of soil cylinders of 120 mm in diameter and 100 nim height. This thick-walled sampler could be dnven down with a sledge hammer by using the SPT proce-dures. These tests were carried out in cased ooreholes just below their bot-tom. It was found out that by using the same impact energy the number of blows was identical with the SPT when a thick-walled sampler was driven from the depth 75 mm to 223 mm (i. e. one half foot). Both methods the SPT method and the method using Czechoslovak soil samplers have been included in the Czechoslovak Standard CSN 73 18 212 "Determination of sand density by dynamie penetration tests", issued in 1959.

Further efforte were directed to find out the correlation in number of blows when different impact energy was applied as individual drilling crews were eąuipped with different hammers, impact