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Penetration testing in Czechoslovakia    esopt

K. Drozd & M. Svasta    State-of-the-art report

The development of methods using penetration principles in the geotechnical aite inyestigations has been directly influenced by the geomorphological and geological conditions of the Czechoslo-vak country. Czechosloyakia, in contrast to most other countries, is charakter-ized by a great yariety of country types alternating in ahort distances. About four fifths of the total area is a rolling countryside with yalleys of the upper or middle couraes of rivers origi-nating in Czechoalovakia. Therefore bed-rock materiała are mostly quite near the earth surfece and the river depoaita, owing to 8hort transportation, are main-ly coopoaed of coarse materiał. Only in aome broad yalleys in the areaa where the rivers leave Czechoslovakia or in local tectonic basins filled with Terti-ary or Ouaternary depoaita is the fine materiał auitabłe for penetration teat-ing. But aa theae lowlands represent the most fertile areas, the industrial or dwełłing centrea have avoided them for a long time ao that no need for speciał aite investigations waa neceasary. Only within the laat decade has a rapid con-8tructional industry overtaken even theae parta of the country.

Map on figurę 1 showa the areaa where penetration testing can be used but even there it can be omitted owing to the testing on undiaturbed soił samples. Tertiary depoaits are composed mainly of clays, siłta, sands with interbeda of gravela. These older depoaita are coyered with eolian deposita - łoesa, alope depoaita - clayey, clayey - aendy and sondy - loamy soila and łoesa loama, fluyial depoaita - aandy gravela, sonda, siłte, 8andy to clayey flood soila, and glaciofluvial and glaciolacustrine depoaits - grayel sands, sands, sandy -loam8 and claya. Areaa of sand deposita piled up by the wind in thickneaaea from 2 to 10 metre8 or sandy lakę or river depoaita where other testing

methods failed are concentrated in re-latiyely smali isles or form narrow and thin atrip8.

At first there was an intention to apply penetration methoda in order to minimize other morę costly methods as for example, in situ piąte loading tests and minimize laboratory testing on undiaturbed soil samples in case the blow-count during aampling would be identi-cal. It was al80 intended to elucidate the atratification of soil layers be-tween boreholea.

The introduction of penetration methods in Czechosloyakia is connected with the Czechoaloyak expert ArnoSt Dyofśk from the National Corporation Stayebnl geologie, Praha, who haa applied the well known Standard Penetration Tests soon after the Second World War. Neyerthe-leae, specific conditions of drilling methoda used in Czechosloyakia led to 8ubatituting the SPT spoon samplers by heayier spoon aamplera which enable aampling of soil cylindera of 120 mm in diameter and 100 mm height. Thia thick-walled 8ampler could be dnyen down with a aledge hammer by using tne SPT proce-durea. These teata were carried out in ca8ed boreholea just below their bot-tom. It was found out that by using the same impact energy the number of blows waa identical with the SPT when a thick-walled 8ampler was driyen from the depth 75 mm to 225 mm (i. e. one half foot). Both methoda the SPT method and the method using Czechoaloyak soil samplers have been included in the Czechosloyak Standard CSN 73 18 21: "Determination of aand density by dynamie penetration teata", isaued in 1959.

Further efforts were directed to find out the correlation in number of blowa when different impact energy was applied as indiyidual drilling crewa were equipped with different hammers, impact