Kenan TÜFEKCİ, Servet DEMİRDAĞ, Nazmi ŞENGÜN, Tamer EFE, Raşit ALTINDAĞ

Kayaçların direkt çekme dayanımlarının indirekt çekme dayanımlarından elde edilmesi için alternatif bir yaklaşım

Son yıllarda yapılan çalışmalar, kayaçların çekme dayanımlarının, üretim yöntemi ve kazı ekipmanı seçimi, patlatma geometrisinin tasarımı, şev stabilitesi ve yeraltı açıklıklarının boyutlandırılması gibi konularda tasarım parametresi olarak etkin bir şekilde kullanılabileceğini göstermiştir. Kaya malzemelerinin çekme dayanımının belirlenmesine yönelik farklı deney yöntemleri kullanılmaktadır. Bu yöntemler, doğrudan ve dolaylı yöntemler olmak üzere iki farklı şekilde uygulanmaktadır. Farklı araştırmacılar tarafından raporlanan deney sonuçları doğrudan ve dolaylı çekme dayanımı değerleri arasında ve hatta dolaylı yöntemlerle elde edilen çekme dayanımı değerlerinin kendi aralarında oldukça farklılık olduğunu göstermektedir. Bu çalışmada doğrudan ve yaygın kullanılan dolaylı yöntemlerden Brezilya testi, 3 ve 4 nokta eğilme deneyleri yapılarak, dolaylı yöntemlerden direkt çekme dayanımını tahmin edecek deneysel katsayılar elde edilmiştir. Ayrıca bu farklılığın nedenini açıklamak için geometrik bir yaklaşım da önerilmiştir. Bu yaklaşıma göre; çekme hasarının oluşması için, numunenin belli bir bölgede aldığı maksimum değerin değil, numunenin çekme gerilmesine maruz kalan hacmindeki ortalama gerilme değerinin etkili olduğu benimsenmiştir. Farklı deney yöntemlerinde farklı boyutlarda numuneler kullanıldığından numunedeki ortalama gerilme, birim hacim başına düşen gerilme şeklinde ifade edilmiş ve her bir dolaylı yöntemdeki ortalama gerilmeyi kolayca hesaplayabilmek için; numunedeki gerilme dağılımını temsil eden ve “karakteristik birim hacim” diye adlandırılan geometrik şekil belirlenmiştir. Bu geometrik şeklin hacmi o deney yöntemi için teorik katsayı olarak önerilmiştir. Karbonat ve mağmatik kökenli kayaçlar için sırasıyla deneysel katsayılar; Brezilya testi için 0.47/0.55, 3 nokta eğilme deneyi (3NED) için 0.29/0.37, 4 nokta eğilme (4NED) deneyi için 0.37/0.43, teorik katsayılar ise; Brezilya testi için 0.5, 3NED deneyi için 0.33, 4NED deneyi için 0.39-0.42 olarak bulunmuştur. Elde edilen deneysel ve teorik katsayıların birbirleri ile uyumlu olduğu görülmüştür

Anahtar Kelimeler:

Çekme dayanımı, Dolaylı çekme dayanımı, Brezilya testi, Eğilme dayanımı, Karakteristik birim hacim

An alternative approach to obtaining the direct tensile strength of the rocks from the indirect tensile strength

Recent studies have demonstrated that the tensile strength of rocks can effectively be used as a design parameter in some subjects such as production method and excavation equipment selection, design of blasting geometry, slope stability, and dimensioning of underground openings. Different testing methods are used for determining the tensile strength of rocks. These methods can be divided into two groups that are direct and indirect methods. According to test results reported by different researchers, the tensile strength of rocks is varying in relation to testing methods. By conducting direct and indirect tests, experimental coefficients which will estimate direct tensile strength from indirect tensile testing methods such as Brazilian, 3-4 point bending tests, are presented in this study. Besides, a geometric approach has been proposed to explain the reason for this difference. This approach claims that it is more important the average stress per unit volume in the tensile zone of the specimen than the maximum stress in the specimen to develop damage. Average stress in the specimen has been expressed as stress per unit volume because each specimen has a different size in different testing methods. To calculate the average stress in a simply way, a geometric shape, which is related to the stress distribution of the specimen and called "characteristic unit volume" has been defined. The volume of the geometric shape has been defined as the theoretical coefficient of the related testing method. For carbonate and igneous rocks, the experimental coefficient was 0.47/0.55 for the Brazilian test, 0.29/0.37 for the 3 point bending test, 0.37/0.43 for the 4 point bending test, respectively. The theoretical coefficient was found to be 0.5 for the Brazilian test, 0.33 for the 3 point bending test, and 0.39-0.42 for the 4 point bending test. Experimental and theoretical coefficients obtained in this study are in accordance with each other.

Keywords:

Tensile strength, Indirect tensile strength, Brazilian test, Flexural strength, Characteristic unit volume,

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