An Experimental Study to Determine the Hoek-Brown Constant (mi) for Tuffs

Year 2021, , 52 - 69, 22.04.2021

Serdar Yaşar

https://doi.org/10.17824/yerbilimleri.771224

Abstract

Nonlinear strength criteria are handy tools for determining the whole range of rock material behavior such as tensile, unconfined compressive, confined compressive and brittle-ductile transition. Hoek-Brown (H-B) failure criterion is one of the most widely used strength criteria for the intact rock material and mi constant is an important parameter of the H-B criterion. The mi constant in the H-B criterion can be determined from reference tables, triaxial compression tests and empirical studies for different rock materials. However, experimental studies for determining the mi constant for tuffs are limited. On this context, a series of triaxial compressive strength tests were carried out on two different tuff samples under varying confining pressures. Using the least squares regression, H-B criterion parameters were computed. As a result, it was seen that computed mi constants were lower than the tabulated constants and unconfined compressive strength of the tuffs were overestimated by the H-B equation. Furthermore, post-failure images of the samples indicated that failure angle increased with increasing confining pressure.

Keywords

Rock mechanics, Hoek-Brown failure criterion, Triaxial compression test, Confining pressure, mi constant

Thanks

I would like to acknowledge Kubilay ALKAN and Mehmet ARSLAN for their efforts during experimental studies.

Tüflerin Hoek-Brown Sabitinin (mi) Belirlenmesi için Bir Deneysel Çalışma

Abstract

Lineer olmayan yenilme ölçütleri, kaya malzemelerinin çekme, basma, yanal basınç altında basma ve kırılgan-sünek geçişi gibi tüm aşamalarını temsil etme noktasında kullanışlı araçlardır. Hoek-Brown (H-B) yenilme ölçütü sağlam kaya malzemesi için önerilmiş olan en önemli ölçütlerden birisidir ve mi sabiti ölçütün önemli bir parçasıdır. Hoek-Brown yenilme ölçütünde farklı kaya malzemeleri için mi sabiti çizelgede önerilen değerlerden, üç eksenli basınç deneylerinden ya da görgül çalışmalardan belirlenebilmektedir. Ancak tüflerin mi sabitinin belirlenebilmesi için yapılan deneysel çalışmalar sınırlıdır. Bu amaçla, iki farklı türde tüf örnekleri üzerinde farklı yanal basınçlar kullanılarak bir seri üç eksenli basınç dayanımı deneyleri gerçekleştirilmiştir. En küçük kareler regresyon yöntemini kullanarak H-B yenilme ölçütünün parametreleri tespit edilmiştir. Sonuç olarak, tespit edilen mi değerlerinin tabloda verilen değerden daha düşük olduğu belirlenmiştir. Ayrıca, tek eksenli basınç dayanımı değerinin H-B denklemi ile gerçek değerden daha yüksek olarak hesaplandığı görülmüştür. Buna ek olarak, yenilme sonrası numune görüntüleri, yenilme açısının artan yanal basınç ile arttığını göstermiştir.

Keywords

Kaya mekaniği, Hoek-Brown yenilme ölçütü, Üç eksenli basınç deneyi, Yanal basınç, mi sabiti

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