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Czech o$lovakia

NeYerthelesa penetration methoda have been used succeasfully many timee for the solution of special problems.

M. Bukovansk^ (1958) ha8 introduced dynamie penetration method in order to de-termine the looaening zonę over an ex-ploited coal aeam due to caYing. Contin-ual penetration in ca8ed boreholea with a cone Dit wa3 carried out to a depth of 60 m below the earth surface. Blows by using an automatically working drop ham-mer were counted for each 20 cm of penetration. The zonę af loosening in the Tertiary depoaita madę of aand, aandy clay, clay and gravela wa8 reliably de-termined.

J. Polśćek (1971) from the Czechoslovak enterpriae ^MVodoho3podśf8k^ rozvoj a Y^ataYba", - Technical and aafety super-vi3ion department - haa introduced a light weight penetration eąuipment ac-cording to the German Standard DIN 4094 for the quality inapection of tena of Iow earthdams of old ponda and lakea in Southern Bohemia, 8orne of which were morę than 600 year old. Cone bit8 of 5 or 10 cm base were driYen into the 8oils of the earthdam by a 10 kg heavy hammer falling free from 50 cm height. The cone angle was 90 degreea. Point re-sistance and wali friction were measured aeparately. Thia enterpriae has recently been trying to introduce the COBRA e-ąuipment for the8e typea of te8ta. Suc-ceasful reaulta were achieYed in the de-termination of local erosion caYitiea along outlet pipes, in the determination of areaa of loose, soft, or little com-pacted soila and the position of the earthdam baae.

V. Bure§ (1968) from the National Enterpriae StaYebni geologie, Praha, haa introduced penetration methoda in order to control the compactneaa of soil layera in newly con8tructed earthdama. The8e teata have been carried out even on aoila m the borrow pita. A good cor-relation waa found between the used penetration methoda and other uaually used inapecting te8ta.

A. Dvofdk (1971) from the same enterpriae haa uaed penetration teating pro-cedure8 in order to determine the bear-ing capacity of either in situ caat pilea or dnven pilea. First of all 8tatic penetration tests with a MAIHAK cone bit were carried out on aoila in a model box. Point resistance and skin friction were measured separately. This research work is still under way.

In SloYakia the exploitation of penetration methoda ror aite inYestigationa is relatively young. Practically it began in 1964 when J. Hlavóćek and J. Magtena from the Research Inatitutę "Y^zkumn^ datav inientfrak^ch staveb_f Bratialava" have used a combined static and dynamie penetration eąuipment ror the determination of bearing capacity of pilea and of the aoil atratification in compli-cated geological conditions in some SloYakian areaa. The specially manufac-tured eąuipment is mounted on a four-wheel chassis on which the power unit and additional dead weight błocka are aaaembled. The lightly moYable eąuipment weights 5 Mp, which in moat caaes was ąuite sufficient. Additional counter-weight against static penetration force can be achieved by four earth anchora. The penetrating apeed was 0.4 m/min both by the manuał and electric power unit procedurę. Point resistance on a

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cone bit with a 10 cm baae and 60 degreea cone angle i8 measured automatically using linear displacement trans-ducer. The resistance is registered on the Brdel & Kjaer level recorder type 2305. The eąuipment for dynamie penetration tests correapond8 to the light apparatus according to the German Standard DIN 4094.