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State-of-the-art report

Penetration testing in Turkey

H. T. Durgunoglu & E. Togrol

The standard penetration test is the most common penetration test in Turkey. Almost every soil exploration program includes standard penetration tests as one of the principle items. Dynamie and static sounding tests are carried out to a rather limited extend. Dynamie sounding test is morę usually employed for smali jobs in order to correlate the site’s soil condition with the already known generał conditions of the area. Static sounding tests, on the other band, used together with standard penetration tests and sampling operations to 1nvestigate the extend of the soil conditions already determined ty the borings.

The most frequently experienced soils in Turkey are overconsolidated stiff clays, sands, gravelly sands. Standard penetration test is invariably used in all these cases. Since expenditure in-volved in performing static penetration test is much less than standard penetration test and exploratory borings, it is preferred particular-ly in soft and loose soils covering large areas. For soft saturated clays, however, vane test is preferred in generał.

Standard penetration test is carried out with the usual standard equ1pment with a 2 inch sampler. Test is performed at the cleaned or washed bottom of boring hole. After the sampling spoon reaches the bottom, the 63.5 kilogrammes drop weight is allowed to fali from a height of 75 centimeters on the top of the drill rods un-til the sampler has penetrated 15 centimeters into soil. The number of blows required to produce that much of penetration is recorded.

Each test consists three steps of 15 centimeters penetration and the total number of blows for the last two steps taken as the standard penetration value.

Contractors are inclined to employ various emprical corrections on the recorded standard penetration yalue. Yet the most common correc-tion now in use is the one suggested by Terzaghi and Peck, for very fine or sil ty, saturated sand. Usually, no quantitative analyses is attempted on sounding data. However, it is considered as a useful tool in determination of the level of bearing stratum. Also allowances are madę when S.P. test is performed in water filled or dril-ling mud filled borę hole. 25-30 meters is considered as the maximum depth for standard penetration testing.

The results of standard penetration tests are required for quick assesment of various strata and soil properties. However, in special cases it is also used in estimation of, for example, pile bearing capacity. Some contractors tend to use standard penetration value together with soil classification to estimate the bearing capacity of driven piles. Principle of such estimates is someway in between static formulae and Meyerhof foemulae using standard penetration value.

Sounding equipment used in Turkey is of old Dutch penetrometer type in generał. Other types of various make and types developed locally are also employed some of which is very useful in determining point and skin frictlons. Almost all equipment has hydraulic pressure transmis-sion system. Although the depth effect is appreciable on blow count no correction is usually employed.

The need for development of standard penetration equ1pment and techniques to overcome errors arising from energy absorption of rods and from presence of water or drilling mud 1n the borę holes acutely felt.