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Bułgaria 22

shaft is seoared by means of a doobie Gardan joint and a Steel bar with alte-rating length. The recording device is a pen rotating aro and the support of the 8zis with the ecoentrio llfter of the applianoe* When in free positions it is few millimeters above the anvil and at eaoh falling of the rammer it is pressed downward and its elongation on whioh the pen is attached shlfts and makes a recording on a paper tape stretohed on a wooden lath. The lath is fixed to the devioe. The roli with the paper tape is fastened to a stay at the lower part of the lath on the top of whioh an attaoh-ment is secured for tape winding at each sinking of the rod length and mounting a new one. Sinoe the paper band is raled at 10 cm and the pen foliowa the rod sinking the number of strokes is regis-tered for 10 cm penetration for eaoh depth level#

Fig. 4. Dynamio pene tronie ter - light

typ©.

The eonieal dynamie penetrometer - super heavy type - is still not applied in our oountry.

3. Test procedurę

3.1. Static penetration testing

At the beginning the work was carried out after the oldest method as recording system was the same for the tip resistance and the to tal penetration resistance. This method was soon abandoned and it is no longer applied. The essential novelty In the newly accepted method of opera-tions is the addition of a second oil chamber with manometer in the measurlng system. One of the oil chamber measures only the soil resistance to the cone penetration and the other - separately the resistance to total penetration. For transmission of the cone pressure force, use is madę of freely moving Steel bars in the ho Ho w penetration rods. The basie advantage of the system is that it renders possibility for simultaneous reading of the tip resistance and the total penetration resistance for each depth level. This method avoids the re-peated interruption during the investiga-tions as was the case prior to accom-plishment of the three types of movement. The investigations aro interrupted only when new rods are mounted. Now with the availability of a tensiometric method for simultaneous reading of the tip resistance and the skin friction the method desoribed by the authors is still applied in Bulgarian praotice with some static penetrometers.

During the investigation of the soil layera under the Black sea water basin the penetrometer was mounted on a heavy f loating pontoon.

The big buckling length of the rods ow-ing to the dis tance from the penetrometer mounted on the floated pontoon to the sea bottom and the water current hampers the norma 1 operation of the statio penetrometer.

After many unsuccessful attempts this obstaćle was overcome by drjyjng drill-ing pipes about 1 m below the sea bottom. Thus the drilling pipes serve as casing of the penetration rods. For avoidlng the drilling pipę buckling at 1 m dis tance are mounted limited direot-ing washers, Owing to their relatively big weight the solid Steel rods were re-placed by pipes. In rough sea the pontoon with the static penetrometer oould not be anchored in a stationary position, owing to which operations were carried out only in calm sea.

3.2. Dynamie penetration testing

As in Bułgaria mainly eonie a 1 dynamie penetrometers are used operating direct-ly from the surfaoe of the terrain, our test at operation with preliminary drilling had to be verified. We praotis-ed preliminary drilling rarely only during operation with tub ul ar penetrometer solely in sound soils. The very simple manner of operation with the eonie al penetrometer gave it preference in our research work. It records the necessary rammer strokes on the anvil for penetration of the standard column into the soil at a depth of 10 cm. For pulling out the rods, use is madę of hand jacks. For making the operation easier we use cones left in the soil.