Investigation into effect of scratch length and surface condition on Cerchar abrasivity index

Yaralı O. | Duru H.

Article | 2016 | Tunnelling and Underground Space Technology60 , pp.111 - 120

The Cerchar abrasivity index (CAI) obtained from Cerchar abrasivity tests is an indicator of abrasiveness of rocks, and widely used for the estimation of bit/cutting tool life and wear rates in various mining and tunnelling applications. The effect of scratch length on CAI is investigated in this study by use of West apparatus and 6 different steel styluses with Rockwell Hardness of HRC40-42, HRC44-46, HRC48-50, HRC50-52, HRC54-56, and HRC58-60. The tests are carried out on 15 different rock samples (sedimentary, igneous, and metamorphic) on which rough and sawn cut surfaces with scratch lengths varying between 2 mm and 20 mm with a . . .n increment of 2 mm, thus resulting in total 27,000 scratches. It is observed that the CAI values between 85% and 93% are reached at the sliding distance of 10 mm while about the final CAI value of 99% is reached at 15 mm. It is also observed that the CAI values on rough surfaces are about 18% higher than those on sawn cut surfaces. Besides, it is determined that the most suitable surface condition in CAI test is sawn cut surfaces according to the coefficient of variation of CAI values in measurement depending on the stylus hardness and the measurement surface condition. © 2016 Elsevier Lt Daha fazlası Daha az

An application of the modified Holmberg-Persson approach for tunnel blasting design

Yilmaz O. | Unlu T.

Article | 2014 | Tunnelling and Underground Space Technology43 , pp.113 - 122

In this study, the applicability of the modified Holmberg-Persson approach for a tunnel blast design was investigated. For this purpose, firstly, a detailed description of the modified Holmberg-Persson approach was made. After that, data collection program for the statistical analysis of the ground vibration parameters induced by the tunnel blasting was presented and then the determination of the critical peak particle velocity level associated with the rock damage was described. Finally, site-specific limiting peak particle velocity values obtained by measuring the overbreak after blasting were given. The results of the field inves . . .tigations were discussed and a new equation to calculate the crushed zone radius was derived. The studies have shown that Holmberg-Persson approach which was originally suggested for perimeter control design technique, can also be applied for a full blasting round to select the proper explosive-hole combinations. © 2014 Elsevier Ltd Daha fazlası Daha az

Prediction of the performance of impact hammer by adaptive neuro-fuzzy inference system modelling

Kucuk K. | Aksoy C.O. | Basarir H. | Onargan T. | Genis M. | Ozacar V.

Article | 2011 | Tunnelling and Underground Space Technology26 ( 1 ) , pp.38 - 45

Impact type excavators are widely used for excavations, performed in weak-laminated-foliated-anisotropic rocks. Therefore the prediction of the performance of impact hammer is very important in many mining and civil engineering projects.This paper describes the construction of adaptive neuro-fuzzy inference system model for predicting the performance of impact hammer type excavator by considering rock and excavating machine properties such as block punch strength index, geological strength index system and impact hammer power. Extensive field and laboratory studies were conducted in the tunnel construction route of the second stage . . .of Izmir Metro Project, which excavated in laminated-foliated flysch rocks. The results of the constructed adaptive neuro-fuzzy inference system and traditional multiple regression models were compared. Although the prediction performance of traditional multiple regression model is high, it is seen that adaptive neuro-fuzzy inference model exhibits better prediction performance according to statistical performance indicators. By means of the developed model, the performance of impact type excavators can be predicted in terms of net excavation based on the selected rock and machine properties. © 2010 Elsevier Ltd Daha fazlası Daha az

The drillability assessment of rocks using the different brittleness values

Yarali O. | Kahraman S.

Article | 2011 | Tunnelling and Underground Space Technology26 ( 2 ) , pp.406 - 414

The brittleness is a fundamental rock property and effective in drilling and rock excavation. Knowing the relations between the drillability and the brittleness will help the rock engineers. For this reason, to investigate the relations between the drilling rate index (DRI) and the different brittleness values, 32 different rock types were tested in the laboratory. Uniaxial compressive strength and tensile strength were determined for the brittleness calculations. The brittleness of B3 (the ratio of compressive strength minus tensile strength to compressive strength plus tensile strength), and the brittleness of B8 (the half of the . . .product of compressive strength and tensile strength) were calculated from the test results. In addition, Sievers' J-miniature drill test and the brittleness test were carried out and DRI values were calculated. Then, B3 and B8 were correlated with DRI values. A good correlation between DRI and the brittleness of B3 could not be found. However, a strong exponential relation between DRI and the brittleness of B8 was found. Comparing the results with the literature showed that there was an agreement between this study and previous studies. It can be concluded that B8 can be used for the assessment of rock drillability. © 2010 Daha fazlası Daha az

Assessment of relationships between drilling rate index and mechanical properties of rocks

Yarali O. | Soyer E.

Article | 2013 | Tunnelling and Underground Space Technology33 , pp.46 - 53

This paper examines the relationships between drilling rate index (DRI) and some mechanical properties of rocks in order to evaluate the effect of strength and indexes of rock on rock drillability. For this purpose, some index properties (in situ Schmidt rebound hardness (SRH), Shore scleroscope hardness (SSH), and point load strength (PLS)) and strength properties (uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS)) values of 32 sedimentary, igneous and metamorphic rock samples were determined. The relationships between DRI and both strength and indexes properties were evaluated using regression analysis and s . . .tatistical methods. As a result, decreasing linear relationships were found between DRI and uniaxial compressive strength, Schmidt rebound hardness, Shore scleroscope hardness, diametral and axial point load strength. © 2012 Elsevier Ltd Daha fazlası Daha az

Predicting performance of EPB TBMs by using a stochastic model implemented into a deterministic model

Copur H. | Aydin H. | Bilgin N. | Balci C. | Tumac D. | Dayanc C.

Article | 2014 | Tunnelling and Underground Space Technology42 , pp.1 - 14

The current study is an attempt to address the stochastic nature of the rock excavation process by suggesting a stochastic performance prediction model implemented into a deterministic model developed for hard rock TBMs. Full-scale linear cutting experiments using constant cross-section and V-type of disc cutters are performed on two different limestone samples to provide the basic input required for the deterministic model used for estimation of instantaneous penetration rate, daily advance rate, thrust and torque requirements of TBMs. Stochastic estimation is performed by using a Monte Carlo simulation program by applying iteratio . . .ns to implement the probabilistic distribution of each model parameter and provide knowledge of a confidence level. Results of the suggested model are verified by measuring the field performance of two earth pressure balance (EPB) TBMs excavating competent rocks in semi-closed mode. The results indicate that the suggested model works well for prediction of instantaneous cutting/penetration rate for both TBMs and both types of disc cutters. However, an improvement on the model is required for estimation of cutterhead torque and thrust of EPB TBMs. The stochastic model implemented into the deterministic model results in almost similar predictions with the deterministic model in 50% (best guess) probability. However, the stochastic modeling provides a tool for exploring the full implications of linear cutting experiments and allows assessing the probability of occurrence and predicting variations of the TBM performance parameters, covering the uncertainties/risks. © 2014 Elsevier Ltd Daha fazlası Daha az

Three dimensional numerical rock damage analysis under blasting load

Yilmaz O. | Unlu T.

Article | 2013 | Tunnelling and Underground Space Technology38 , pp.266 - 278

In this study, the behaviour of rock mass subjected to blasting load is investigated using three dimensional finite difference numerical modelling. In the analyses, Mohr-Coulomb failure criterion has been used for the characterisation of the rock mass strength. Stresses acting on the borehole boundary have been simulated by an exponential function which reaches its maximum within a short time and then falls to zero value in a considerable period. The strain rate effect on the mechanical properties of rock material has also been taken into account in the analyses. Different explosive and site conditions have been studied to investiga . . .te the effects of loading rate and anisotropic high in situ stresses on blasting performance and blast induced damage zones. Results have shown that the most efficient explosive in rock blasting will be the one with low frequency content but with a sufficiently high borehole wall pressure. In addition, it has been verified that the directions and the magnitudes of major principle stresses affect the development of the crack zone around the borehole. Finally, it has been seen that proposed equation for the dynamic compressive strength of rock material fits very well to general suggestions. © 2013 Elsevier Ltd Daha fazlası Daha az

Effect of Poisson's ratio on the normalized radial displacements occurring around the face of a circular tunnel

Unlu T. | Gercek H.

Article | 2003 | Tunnelling and Underground Space Technology18 ( 5 ) , pp.547 - 553

The distribution of displacements occurring around the advancing face of a tunnel is one of the widely discussed topics in tunnelling. Unavailability of a closed-form solution for this problem has directed the researchers to the utilization of numerical analyses mainly. In this study, a three-dimensional finite difference stress analysis program, i.e. FLAC3D, has been employed for determining the variation of radial boundary displacements along the longitudinal direction of a circular tunnel located in a hydrostatic in situ stress field. According to the results for a linear elastic material behavior, the normalized radial displacem . . .ents occurring in the vicinity of the face are affected by Poisson's ratio of the surrounding medium. In addition, it has been noted that, depending on Poisson's ratio, the value of elastic pre-deformation occurring at the face ranges between 20 and 30% of the final tunnel deformation occurring far from the face. Furthermore, expressions obtained by non-linear curve fitting are presented for the normalized radial displacements occurring ahead of and behind the excavation face of the tunnel. © 2003 Elsevier Ltd. All rights reserved Daha fazlası Daha az

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