Bildiri ve Sunum Koleksiyonu
Bu koleksiyon için kalıcı URI
Güncel Gönderiler
Öğe Determining REV for jointed rock masses using finite numerical analysis(CRC Press/Balkema, 2024) Chiu, J.K.Y.; Sarı, MehmetThe representative elementary volume (REV) of a jointed rock mass can be determined using finite numerical analysis, but the effect of using different finite element model settings has not been widely studied. This paper aims to compare various finite element codes and their settings for determining the REV size of an excavated jointed rock mass. We used the scriptable, free program ADONIS and Rocscience's RS2 and RS3 to numerically analyse circular excavation in a rock mass intersected by orthogonal joint sets with specified joint spacing. While the determined REV sizes versus the opening diameter to joint spacing ratio are generally comparable for all analyses, the use of XFEM in RS2 results in a relatively larger REV size. Considering computation efficiency, a 2-dimensional, efficient, and representative finite element model for a complete range analysis to obtain a reliable REV size of a jointed rock mass is preferred over a 3-dimensional analysis.Öğe A simple approximation to estimate the hoek-brown parameter 'mi' for intact rocks(2010) Sarı, MehmetA very useful approximation for the estimation of the Hoek-Brown material constant mi is presented in this study and the basic logic behind it is evaluated in detail. The study clearly indicates that the Hoek-Brown material constant mi can be approximately predicted from the ratio between the uniaxial compressive strength and tensile strength of brittle intact rocks. By introducing the brittleness ratio of ?c/?t into the generalized Hoek-Brown failure equation instead of the material constant mi , which, actually, has a fundamental importance, a practical formulation is suggested for this commonly employed failure criterion. © 2010 Taylor & Francis Group.Öğe Numerical modelling of mechanized longwall mining with top coal caving in aegean lignite establishment(Chamber of Mining Engineers of Turkey, 2013) Yaşıtlı, Nazmi Erhan; Bayram, Fatih; Ünver, Bahtiyar; Kavaklı, NevzatEffective caving of top coal is the most critical factor in maintaining an efficient production in longwall with top coal caving method. During production of the top coal by caving, considerable amount of coal may be left in the goaf and in addition, the produced coal may be diluted with rock, consequently, decreasing the extraction ratio and production efficiency. In this study, numerical studies associated with numerical modelling of Eynez Underground Mine have been carried out. Firstly, the longwall panel was modelled by using a software called FLAC3D, developed based on finite difference technique. Secondary, the induced stresses developing around the longwall face have been determined. Finally, the most critical step of production that is top coal caving through the frames of shields has been modelled. In Eynez Underground Mine, top coal was sufficiently fractured but the marl at the roof was not fractured and there occurred a big opening after caving of top coal. In order to achieve efficient and quick production, the marl must be cracked in as uniformly sized pieces as possible.Öğe Stochastic estimation of the Hoek-Brown strength parameters using spreadsheet models(International Society for Rock Mechanics, 2012) Sarı, MehmetEmpirical models are being frequently used to estimate rock mass mechanical properties. It is well known that most empirical methods in rock engineering give averaged values, and that it might be significant variation between the lowest and highest value. Besides, it is highly important to describe relations between input parameters in an empirical model if one wants to obtain accurate results during stochastic analysis. In this paper, we run two different Monte Carlo simulations for the comparison of results generated from empirical Hoek-Brown failure criterion. First simulation model assumes all input parameters used in the criterion as independent variables and second model includes the relationships between input parameters via a correlation matrix. The correlation matrix used in the simulations is succeeded by consulting knowledge of some experts in the field of rock engineering. It is found that with or without considering correlations, the mean values of simulation outputs computing the rock mass strength parameters are not notably different. However, the standard deviations of strength parameters are generally smaller in simulation results taking into account of correlations between input parameters. It is concluded that in a stochastic estimation study, defining the relationships between input parameters would not change the simulation results drastically. © BeFo and ISRM, 2012.Öğe Incorporating Variability and/or Uncertainty of Rock Mass Properties into GSI and RMi Systems Using Monte Carlo Method(Springer, 2015) Sari, Mehmet; Lollino, G; Giordan, D; Thuro, K; CarranzaTorres, C; Wu, F; Marinos, P; Delgado, CThis paper introduces a probability-based methodology that can be used to evaluate alternative approaches on account of the uncertainties associated with predicting the rock mass properties. The use of this methodology is illustrated through its application for two rock mass case studies. In this regard, the probabilistic spreadsheet models are developed for the strength estimation of Kizilkaya ignimbrite and New Zealand greywacke. The frequency histograms and/or the density functions that best describe the data distribution are used as inputs in GSI and RMi systems. This approach allows the variability and/or uncertainty of the available data to be adequately taken into account during simulations. The developed spreadsheet models are also used to quantify the influence of various material and discontinuity characteristics on the resultant strength properties of the studied rock masses. Sensitivity analysis explicitly shows that joint spacing and UCS of intact rock are the most effective parameters on the estimated rock mass strengths.Öğe Comparison of Turkish coal mining safety indices with world countries(Uceat-Chamber Mining Engineers Turkey, 2007) Sarı, Mehmet; Karpuz, C; Hindistan, MA; Tercan, AEComparing its safety statistics with other countries one can conveniently assess the condition of a country in terms of occupational health and safety. In this study, it is aimed to evaluate the safety performance of Turkish coal mining industry by comparing its statistics with safety figures of some coal producing countries. The safety numbers of person injured and person deaths per million tons of coal produced, per thousand employees at work and per million hours of work were determined graphically for Turkey, USA, India, Poland, Australia and S. Africa. In the analysis, Turkish data were separated into three components as TKI, SSK and TTK in order to reflect the safety conditions of different sectors in this country. The collected data for all countries were averaged across last fifteen years in attempt to remove some of the statistical variations caused by annual fluctuations. According to statistical results, TKI compares well with the safety performance of other countries due to its lower fatality and injury rates, especially for per million tons of coal production and per thousand employees at work. On the other hand, TTK and SSK showed the highest rates in all figures comparing accident data owing to facts that its harsh working conditions of the former and its different reporting system of accident occurrences of the later.Öğe Estimating strength of rock masses using fuzzy inference system(CRC Press/Balkema, 2016) Sarı, MehmetThis paper describes how to apply fuzzy inference system (FIS) to estimate the strength of field scale rock masses by judgment and experience of practicing engineers. Three important parameters believed to influence the rock mass behavior namely intact rock strength, block size, and joint surface condition are defined as fuzzy variables. The strength of jointed rock masses is then estimated by incorporating different combinations of three fuzzy inputs into Mamdani rule-based FIS model. To validate the accuracy of the model results, a comprehensive rock mass data is collected from the literature and the strength of rock masses estimated using different empirical equations is compared to the strength of rock masses estimated from the FIS model. It is concluded that the newly developed model compares well with the estimated results and it can be recommended as an alternative method for the rock mass strength predictions instead of empirical approaches in practice. © 2016 Taylor & Francis Group, London.
