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Bułgaria 21

dynamie panatrom©ter operating directly on tba surfaoe of the ground appeared to as morę applioable. That is why we di-reeted our attention towards this typa of penetrometer. The existlng construc-tions abroad dld not meet our needs. They were of the light type either with manuał lifting of the rammer whioh reąuires hard physical efforta or with oomplex mechanized construotions. In the seoond case, the deyioes ara heavy₉ oomplex and do not operate always precisely* While in the existing devioes the rammer, whioh had to be lifted manually, is 10 kp in weight, aoeording to the Bulgarian State Standard 899^-70 - it is 20 kp.

For securing the same amount of work (500 kp/enr; in the first oase the rammer should be lifted at a height of 50 cm and in the seoond oase - 25 om* It is evident that manuał lifting of the rammer - 20 kp - during oontinuous operation is impossible* An object was set forth to design a construotion whioh will meet the reąuirements for compulsory parame-ters aooording to the Bulgarian State Standard 899^-70 with slmple means*

The dynamie penetrometer used at present in Bułgaria is with eccentrio lifting of the rammer* The eeoentric lifter has the contour of Arohimedian spiral. At the beginning this penetrometer was designed to operate as light type* Very soon, however, we found out that operation with it is very light (Fig* 2) and the rotary motion may be produced by one worker* For converting the light type

Fig* 2* Operation with the dynamio penetrometer light type.

into a heavy one the rammer had to be not 20 kp but 50 kp* This was aooom-plished by adding a weight of 30 kg on the existing rammer* For seouring a height of 50 om instead of 25 om for free falling of the rammer we replaoed the mobile bridge with ram and handle with another ram whioh lifts the rammer at 50 om* The guiding rods had also to be lengthened up to 2 m. As a result the dynamie penetrometer obt8ined the ap-pearanoe shown on Fig* 3*

Fig. 3* Dynamio penetrometer - heavy type.

It should be pointed out that while the operation with the dynamio penetrometer is easy and does not reąuire partieular efforts, the operation with the heavy type reąuires physical labour of two workers. This called for detaohment of the dynamio penetrometer from the oom-bined oonstruotion and for its mechani-zation* Besides the ezperienoe suggested that under Bulgarian oonditions of main-ly shallow foundation, use is madę most often of the dynamie penetrometer -light type* After its detaohment from the combined construotion it beoame still limiter and weighs only 63 kg. By attaohing two wheels and a handle to the base the device oan easily be moved with the rods and other acoessories on it(ft$t4.

The meohanized aotivating of the dynamio penetrometer was aooomplished by means of interna1 oombustion engine the revolu-tions of whioh are reduoed to the neces-sary 10-30 rev/min. with the aid of a reduotor* The rotary motion of the ram