Rock quality designation-fracture intensity index method for geomechanical classification
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ORIGINAL PAPER
Rock quality designation-fracture intensity index method for geomechanical classification Zekai Şen
Received: 26 January 2013 / Accepted: 17 May 2013 # Saudi Society for Geosciences 2013
Abstract Rock quality designation (RQD) is a simple and effective way of rock mass classification from surface scanlines or preferably borehole measurements. A major drawback in its classical use is that only one representative RQD value is obtained from the field measurements per core run. However, it is shown in this paper that the field measurements along a scanline provide detailed information about the rock quality and the fracture intensity (FI) for a given number of joints. In order to be able to extract the complete information concealed within the field data, the RQD-fracture index diagram concept is proposed and applied to actual field scanline measurements from England. The basis of the suggested procedure is to obtain a series of all possible RQD and FI values from given intact length measurements. This procedure provides additional information as to the local zones of heterogeneities within the rock mass and a new way of rock classification on the basis of the combined effects of RQD and FI. It is also possible to calculate percentages of different rock qualities within the same rock mass. Keywords Classification . Fracture index . RQD . Rock . Quality . Scanline
Introduction In localized and extended engineering structures, the geological conditions are important to be assessed because they have influence at different phases, from the feasibility to planning, design, construction, and safety of these structures. Therefore, reliable evaluation of geomechanical Z. Şen (*) Civil Engineering Faculty, Istanbul Technical University, Maslak, 80626, Istanbul, Turkey e-mail: [email protected]
properties of rock mass requires considering a number of parameters like degree and grade of weathering, structure, discontinuity types, occurrence, distribution, orientation, etc. which are essential for comprehensive precise classification of rock masses. Not only the collection of data to assess the geomechanical rock mass quality essential but also the selection of the suitable classification system and parameters is vital in engineering studies. The application of the classification system should also be indicated so as to see how suitable to the intended engineering purpose. Naturally fractured rocks present complex patterns of discontinuities such as fissures, fractures, cleavages, faults, etc., which reduce the stress and strain behaviors of the original intact rocks in an undesirable manner. The discontinuities arise due to different reasons such as folding, faulting, thermal cooling, tectonic activity, earthquakes, and chemical solution. Their quantification for engineering purposes poses difficult problems which cannot be dealt with the analytical techniques in a unique and deterministic way leading to firm decision variables such as the strength of the rock. Geomechanical properties of rock masses are assesse
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