Ozgur Yilmaz

Bu çalışmanın temel amacı, kaya veya beton ve harç gibi malzemelerin önemli mekanik özellikleri arasında yer alan dolaylı çekme ve doğrudan çekme dayanımlarının tane yapısına bağlı olarak nasıl bir değişim gösterdiklerini araştırmaktır. Bu çalışmada yapılacak deneyler için çeşitli boyut aralıklarında kum, çimento ve su kullanılarak yapay örnekler hazırlanmış ve tek ve üç eksenli basınç dayanımı ve doğrudan ve dolaylı çekme dayanımı deneylerine tabi tutulmuştur. Sonuç olarak, çok sayıdaki örnekler üzerinde gerçekleştirilen doğrudan ve dolaylı (Brezilya) deneylerinden elde edilen sonuçlar içsel sürtünme açısı ve tane boyutunun, kaya malzemelerinin dolaylı çekme dayanımı ve doğrudan çekme dayanımı üzerindeki etkilerini belirgin olarak göstermektedir.

In the mining industry, bench blasting efficiency is determined by rock fragmentation. Therefore, it is crucial to predict the result of rock fragmentation before blasting. It is widely accepted that empirical fragmentation models like Kuz-Ram and Chung and Katsabanis (C&K) are the most reliable tools for predicting the size distribution of rock fragments following blasting. The main aim of this study is to provide an approach to estimating the optimal burden according to the intended mean fragment size using rock fragmentation models. It is necessary to determine or know the rock factor used in the mentioned models in attempting to apply the method proposed in this study. Initially, studies were conducted to determine the most appropriate burden according to the intended mean fragment for a quarry where the rock factor is known. After this, simplified equations were derived for the optimal burden depending on the rock factor, the intended mean fragment size, the bench height and the density of the explosive.

The Karadon mine, where field studies were carried out, is located in the north west of Turkey and is considered to be a highly gaseous coal mine. Explosives and ignition systems used in underground coal mines are determined by laws, statutes, regulations and strict rules. Restrictions arising from legal requirements, such as restrictions on charging and stemming lengths and blasting agents to be used, make the use of well-known tunnel blasting techniques difficult or sometimes not possible. In such cases, the designs made with the equations given in the literature must be revised and rearranged. The objective of this study is to recommend solutions to the blasting difficulties that are encountered in gaseous underground coal mines in which there are limitations arising from legal requirements. This study summarizes and analyses the blasting practices currently employed at Karadon mine along with their disadvantages. New blasting designs were then made using the methods suggested in the literature, and these designs were revised according to legal requirements. By keeping the charge concentration constant relative to its original value, the burden and spacing distances were adjusted. As a result of this study, it has been seen that rearrangement by keeping the charge concentration constant compared to its original value is an appropriate engineering solution.

Since direct tensile testing is time-consuming and expensive, the Brazilian test may overestimate the tensile strength of rocks because of its biaxial stress instead of the uniaxial tension condition, an alternative testing method is required to determine tensile strength of intact rock samples. The aim of this paper is to introduce a new push–pull tensile testing apparatus (PPTA), which can be used for determining direct tensile strength of cylindrical intact rock specimens. The PPTA introduces a new clamping mechanism that can also be utilized for the determination of conventional direct tensile strength of intact rock specimens. During the study, direct tensile tests and indirect Brazilian tests were carried out using rock specimens and artificial rock specimens that were made by using graded river sand, cement, and water mixtures to compare results obtained from the PPTA tests. Results of the experimental study have shown that there is a good correlation between the results obtained from the direct tensile tests and the PPTA. In addition, elastic and elasto-plastic numerical modeling studies were also carried out using the three-dimensional finite difference method (FLAC 3-D) to investigate stress development within rock sample during testing and failure initiation. Results of the modeling studies showed that failure of the core sample is due to maximum principal tensile stresses and crack initiation starts from the outer periphery of the core and propagates inside the center, which is an acceptable failure mode for direct tensile testing. Finally, results of the experimental and numerical studies have shown that push-pull tensile testing apparatus (PPTA) is a practical and reliable tool for determining direct tensile strength of intact rocks. Because it does not require sample preparation, it can easily be used either in laboratory or in situ.