Incorporation of uncertainty in estimating the rock mass uniaxial strength using a fuzzy inference system
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ORIGINAL PAPER
Incorporation of uncertainty in estimating the rock mass uniaxial strength using a fuzzy inference system Mehmet Sari 1 Received: 1 May 2018 / Accepted: 14 December 2018 # Saudi Society for Geosciences 2019
Abstract Due to its complex nature and inherent uncertainty, it is very hard to directly measure the uniaxial strength of jointed rock masses. In rock mechanics, it is a necessity to employ empirical equations and numerical methods for the estimation of rock mass uniaxial strength. In addition to the existing empirical equations and numerical methods, it is essential to pursuit approaches to incorporate uncertainty in estimating rock mass uniaxial strength. One of the promising techniques pertinent to such situations is the fuzzy inference system (FIS). In the application of FIS, it is expected that the problem or system under investigation should be uncertain and fuzzy, and calculations are drawn mostly from judgment and experience, rather than mathematical expressions. This study proposes a new method of estimating the rock mass uniaxial strength using fuzzy sets theory. For this purpose, three dominant elements essential for the determination of rock mass uniaxial strength; i.e., intact rock uniaxial strength, block size, and joint surface condition, were evaluated as fuzzy variables in the analysis involving the assignment of proper membership functions. A logical and systematic combination of three input variables was employed under a Mamdani rule-based FIS environment, which explicitly takes into account the expert knowledge using built lookup charts. To check the accuracy of the FIS model estimates, an extensive data set was compiled from the published sources. This data set used in the analysis covered a wide range of rock mass types in typical rock engineering projects. It was seen that the uniaxial strength values estimated by the proposed FIS model were mostly in fair agreement (R2 = 0.77) with those estimated by well-known empirical equations. Keywords Rock mass uniaxial strength . Fuzzy logic . Fuzzy inference system . Empirical equations
Introduction Estimation of rock mass strength plays a critical role in the preliminary analysis and design of rock structures, such as dams, roads, bridges, tunnels, and underground excavations. Erroneous results may lead to overestimating or underestimating rock mass strength, which can have catastrophic consequences on the stability of these structures. Therefore, one of the greatest challenges in rock mechanics and engineering is the determination of rock mass strength at field scale. Since rock masses are comprised of intact rock blocks separated by tightly interlocking discontinuities (Fig. 1), it is unlikely to conduct physical tests on samples of comparable size to a rock mass into which engineering * Mehmet Sari [email protected] 1
Department of Mining Engineering, Aksaray University, 68100 Aksaray, Turkey
structures are excavated. However, the stability of these structures is highly dependent on the strength behavior of rock mas
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