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    Assessing deformability of siltstone under compressive loading by ultrasonic wave propagation
    (2011) Karakus M.; Tutmez B.
    Determination of stress-strain behaviour of rocks plays a crucial role in understanding the response of rocks during loading. However, it is a tedious, expensive and a time-consuming process to obtain such characteristics both in the laboratory and in situ. On the other hand, non-destructive testing methods such as ultrasonic velocities can produce a reliable and fast solution to indentify state of strain and stress in rocks. The present paper aims to provide insight into the relations amongst ultrasonic wave velocities, amplitudes and deformability properties of porous siltstone under compressive loading. For this purpose, pulse (v P) and shear wave velocities (v S) along with amplitudes (AP - AS), and applied loads with resultant strain were measured simultaneously so that response of siltstone to compression can be evaluated. In addition, initial v P and v S were recorded at the beginning of each test to calculate dynamic elastic properties of the specimens. This provided a comparison between static and dynamic elasticity properties of siltstone. Crack damage associated with the onset of dilation was also investigated. The results showed that there is a non-linear logarithmic relation between velocities and stress-strain level for siltstones.
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    An overview of Turkish lignite qualities by logistic analysis
    (2013) Tutmez B.; Hozatli B.; Cengiz A.K.
    As an indispensable energy source, lignite is almost exclusively used in power generation in Turkey. To assess the quality level of Turkish lignite, a multivariate statistical analysis was conducted. The relationship among the lignite quality parameters has been investigated using a response method that is the logistic regression method. The analysis determines the effect of multiple predictor variables such as moisture, ash and sulphur presented simultaneously to predict membership of the two calorific value categories. By this way, a reliable binary response regression structure was constructed considering all the lignite fields in Turkey. Both the experiments on identifying the influential measurements and the measure of goodness of fit indicated that the overall model has a big capability to exhibit the relationship among the parameters of the Turkish lignite. © 2013 The Editorial Office of Journal of Coal Science and Engineering (China) and Springer-Verlag Berlin Heidelberg.
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    Residual-based evaluation for spatially-varying processes
    (TMMOB Maden Muhendisleri Odasi, 2017) Tutmez B.
    Evaluation of variability in a mining site is one of the main motivations of geosciences uncertainty analysis. In parameter estimation, both maximum-likelihood-based methods and ordinary least squares (OLS) correspond constant variance, which is the variability of a measurement is the same in any case of the values of the explanatory variables connected with it. When the assumption of constant variance is not satisfied, a data transformation and use of generalized least squares regression (GLS) is required. GLS approach considers the inequality of variance in the measurements. In the present study, GLS fitting is performed by residual maximum likelihood (REML) method in which each observation is represented additively in terms of fixed and random effects. By using the Bauxite Mine data, the performances of the REML-based GLS model are also compared with conventional Geographically Weighted Regression (GWR) Model performances and the results are discussed.