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Czechoslovakia 30

Neyerthelesa penetration methoda have been uaed successfully many timeo for the aolution of apecial problems.

U. Bukoyansk^ (1958) haa introduced dynamie penetration method in order to de-termine the loosening zonę over an ex-ploited coal aeam due to caving. Contin-ual penetration in ca8ed boreholea with a cone Dit wa8 carried out to a depth of 60 m below the earth surface. BIowa by uaing an automatically working drop ham-mer were counted for each 20 cm of penetration* The zonę af loosening in the Tertiary depoaita madę of 8and, aandy clay, clay and gravels waa reliably de-termined.

J. Polóćek (1971) from the Czech08lovak enterpriae ^MVodoho8podśfak^ rozvoj a y^stayba", - Technical and safety auper-yision department - haa introduced a light weight penetration equipment ac-cording to the German Standard DIN 4094 for the ąuality inapection of tena of Iow earthdama of old ponda and lakea in aouthern Bohemia, some of which were morę than 600 year old. Cone bita of 5 or 10 cm baae were driven into the aoila of the earthdam by a 10 kg heavy hammer falling free from 50 cm height* The cone angle waa 90 degreea* Point re-sistance and wali friction were meaaured aeparately. Thi8 enterpriae haa recently been trying to introduce the COBRA e-ąuipment for tneae typea of te8t8. Suc-ceaaful reaulta were acnieyed in the de-termination of local eroaion cayities along outlet pipes, in the determination of areas of looae₉ soft, or little com-pacted 8oils and the poaition of the earthdam baae*

V. BureS (1968) from the National Enterprise Stayebnf geologie, Praha, haa introduced penetration methods in order to control the compactness of soil layers in newly constructed earthdama. These tests have been carried out even on

soils in the borrow pita* A good cor-relation waa found between the used penetration methods and other usually used inspecting tests.

A. Dyofdk (1971) from the same enterpriae has used penetration testing pro-cedures in order to determine the bear-ing capacity of either in situ cast piles or driyen piles. First of all static penetration tests with a MAIHAK cone bit were carried out on soils in a model box* Point resistance and skin friction were measured separately. Thia reaearch work i8 atill under way.

In Slovakia the exploitation of penetration methods ror site investigations is relatiyely young. Practically it began in 1964 when J. Hlayóóek and J. MaStena from the Research Institute "\tyzkumn^ datav inien^rak^ch stayeb, Bratislaya" have used a combined static and dynamie penetration eąuipment for the determination of bearing capacity of piles and of the soil stratification in compli-cated geological conditions in some Sloyakian areas* The specially manufac-tured eąuipment is mounted on a four-wheel chassis on which the power unit and additional dead weight błocka are assembled. The lightly movable eąuipment weights 5 Mp, which in most cases was ąuite sufficient. Additional counter-weight againat static penetration force can be achieyed by four earth anchora* The penetrating speed was 0*4 m/min both by the manuał and electric power unit procedurę. Point resistance on a cone bit with a 10 cm base and 60 de-grees cone angle is measured automatically using linear displacement trans-ducer. The resistance is registered on the Brtlel & Kjaer level recorder type 2305. The eąuipment for dynamie penetration tests corresponds to the light apparatus according to the German Standard DIN 4094*