Geomechanics and Engineering

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A new rock brittleness index on the basis of punch penetration test data

  • Ghadernejad, Saleh (School of Mining Engineering, University of Tehran) ;
  • Nejati, Hamid Reza (Rock Mechanics Division, School of Engineering, Tarbiat Modares University) ;
  • Yagiz, Saffet (School of Mining and Geosciences, Nazarbayev University)
  • Received : 2019.11.09
  • Accepted : 2020.04.07
  • Published : 2020.05.25
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Abstract

Brittleness is one of the most important properties of rock which has a major impact not only on the failure process of intact rock but also on the response of rock mass to tunneling and mining projects. Due to the lack of a universally accepted definition of rock brittleness, a wide range of methods, including direct and indirect methods, have been developed for its measurement. Measuring rock brittleness by direct methods requires special equipment which may lead to financial inconveniences and is usually unavailable in most of rock mechanic laboratories. Accordingly, this study aimed to develop a new strength-based index for predicting rock brittleness based on the obtained base form. To this end, an innovative algorithm was developed in Matlab environment. The utilized algorithm finds the optimal index based on the open access dataset including the results of punch penetration test (PPT), uniaxial compressive and Brazilian tensile strength. Validation of proposed index was checked by the coefficient of determination (R2), the root mean square error (RMSE), and also the variance for account (VAF). The results indicated that among the different brittleness indices, the suggested equation is the most accurate one, since it has the optimal R2, RMSE and VAF as 0.912, 3.47 and 89.8%, respectively. It could finally be concluded that, using the proposed brittleness index, rock brittleness can be reliably predicted with a high level of accuracy.

Keywords

Acknowledgement

The authors would like to thank the students and staff at the Earth Mechanics Institute, Colorado School of Mines, too numerous to mention, whose work over the last couple of decades has led to the currently existing rock test database.

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