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DOI: /LE/10/3-4/9 Landscape & Environment 10 (3-4) ROCK MASS RATING IN BÜKK MTS., N HUNGARY BASED ON PETROPHYSICAL PARAMETERS AND PARTING CONDITIONS RICHARD WILLIAM MCINTOSH* BALÁZS ENCS Department of Mineralogy and Geology, University of Debrecen, H-4032 Debrecen, Egyetem tér 1., Hungary * Received 8 July 2016, accepted in revised form 10 September 2016 Abstract In the region of Bánkút and Ómassa, Bükk Mountains the strength of the rocks of 29 outcrops was studied based on Rock Mass Rating (RMR). Strength of the rock masses showed no correlation with the material of the Formations they exposed, however, correlation between the orientation of valleys and ridges and the location of the most deformed rocks and thus that of the rock masses with poorest qualification could be observed. Keywords: unconfined compressive strength, parting, rock mass rating, Bükk Mts. 1. Introduction Studying the relationship between geological conditions and the geomorphology of a landscape has always been in the focus of geomorphology research (Gerasimov 1946; Birot 1958; Twidale 1971). The relationship between structural and morphological elements was analysed on the basis of morphotectonic studies (Scheidegger 1980, 2001; McIntosh 2014) while others considered the relationship between the strength of rocks and slope conditions responsible for forming the morphology of an area (Selby 1980; Telbisz 1999; Püspöki et al. 2005; Demeter Szabó 2008a, b). This latter group of research used generally one single parameter, unconfined compressive strength (UCS) to describe the strength of the geological medium forming an area. In the present paper an attempt is made to use rock strength determined on the basis of several parameters in studying the relationship between geology and morphology in a study area. Parameters applied for determining rock strength are taken from engineering practice where they have been applied primarily for artificial rocks, drill cores and artificial establishments to be built in natural rock masses (road and railway cuts, tunnels, etc.). The authors believe that the strength of rocks forming the geological setting of an area could be described in a much more complex way using six parameters than on the basis of a single frequently measured in laboratory parameter. 2. Material and methods Relationship between the geology and morphology of the study area located in the Bükk Mountains, North Hungary (Fig. 1) is studied on the basis of rating the rock mass of 29 outcrops (Table 1). The study area located in and around the Garadna Valley between the Big and Little Plateaus is composed of numerous Palaeozic 162 Landscape & Environment 10 (3-4) Fig. 1. Location of the study area in Bükk Mts., N Hungary and Mesozoic formations. The limestone and dolomite rocks of 5 of these formations were involved in the field measurements (Table 2). Studied outcrops were evaluated on the basis of 6 parameters in the Rock Mass Rating system (Table 1) established by Bieniawski (1973) and further developed by (Gálos Vásárhelyi 2006). Unconfined compressive strength, RQD values and the distance between parting surfaces were directly measured in the outcrops. State of parting surfaces, presence of water and the direction of parting surfaces were evaluated by field inspection. In order to estimate unconfined compressive strength in the field surface hardness measurements were performed using a Proceq Silverschmidt N type Schmidt hammer. Outcrops were divided into sections and 10 measurements were made in each section. Averages of the sections were also averaged for the entire outcrop. Volume of parting was determined based on Rock Quality Designation (RQD) value developed by Deere (1969) initially for measuring cores. According to the formula below, the ratio of continuous sections longer than 10 cm (without parting) is calculated compared to the total length of the rock mass: where h10= length of the continuous rock sections longer than 10 cm without parting, h= length of the total studied outcrop section. Both horizontal and vertical RQD values were measured and averaged. Distance of partings was measured in every section of the outcrops and all sections were given a score in points that were averaged for the whole outcrop. State of parting surfaces, the presence of water and the orientation of partings were evaluated for each section of the outcrops and for the whole outcrop as well. Regarding the score of each parameter in the original RMR system a total of 100 points could be scored by one rock mass. In the system presented here, however, the maximum score is 120 points due to the Landscape & Environment 10 (3-4) Table 1. Rock Mass Rating (RMR) system modified after Török (2007) UCS (MPa) 1 score Horizontal RQD (%) 50 score Vertical RQD (%) 50 score Distance between partings (m) 0.06 State of parting surface presence or water on parting surface score Very rugged, not continuous, fresh rock Slightly rugged, open 1mm, slightly weathered Slightly rugged, open 1mm, strongly weathered Fault, open 1-5mm Clay filled fault plane, open 5mm score dry moist wet drops of water flowing water score Parting orientation very good good adequate bad very bad score Class of rock mass I II III IV V Qualification very good good satisfactory poor very poor Rock Mass Rating 20 addition of horizontal RQD values therefore the original assessment categories have been slightly modified as well (Table 1). Petrographic description of the rock samples is given on the basis of microscopic analysis performed using a Nikon Microphot SA research microscope in the laboratory of the Department of Mineralogy and Geology, University of Debrecen. 3. Results and discussion Strength of natural rock masses in 29 outcrops has been studied in the Garadna Valley in the Bükk Mts. In the modified RMR system outcrops scored between 16 and 67 points (Table 2). Table 2 shows that the outcrops are composed mainly of limestone and dolomite that are regarded to be very good considering rock strength in the literature. Rock masses with best score are exposed far from each other and their material is classified into different formations. Their score of 67 and 65 points classify them into the top part of the satisfactory category (category III). Almost 60% of the outcrops received this satisfactory qualification while almost 40% of them were qualified as poor (category IV). One outcrop (Borovnyák 18) was qualified very poor (category V). Unfortunately no outcrops scored higher than satisfactory qualification. Based on literature data regarding the Bükk Mountains, the average unconfined compressive strength of Palaeozoic and Mesozoic carbonates is around 98 MPa (Püspöki et al. 2005) thus high strength was expected regarding the rocks of the studied outcrops. In contrast no outcrops scored 164 Landscape & Environment 10 (3-4) Table 2. Rock Mass Rating (RMR) system modified after Török (2007) Outcrop name Rock Formation RMR score Rock of outcrop Outcrop name Mályinka 3A Mályinkai 52 Limestone Borovnyák 21 Mályinka 3B Mályinkai 67 Limestone Borovnyák 22 Mályinka 4 Mályinkai 58 Limestone Borovnyák 23 Borovnyák 2 Borovnyák 2a Borovnyák 5 Borovnyák 7 Borovnyák 8 Borovnyák 12 Borovnyák 14 Borovnyák 15 Borovnyák 17 Borovnyák 18 Borovnyák 19 Borovnyák Limestone Borovnyák Limestone Bánkút 1 38 Limestone Bánkút 2 53 Limestone Ómassa 1 53 Limestone Ómassa 2 56 Limestone Ómassa 3 32 Limestone Ómassa 4 31 Limestone Ómassa 5 43 Dolomite Ómassa 6 16 Dolomite Ómassa village 1 38 Dolomite Ómassa village 2 43 Dolomite Rock Formation Nagyvisnyói Mészkő Nagyvisnyói Mészkő RMR score Rock of outcrop 31 Limestone 53 Limestone 65 Limestone 56,5 Limestone 41 Limestone 50 Limestone 28 Limestone 46 Limestone 36 Limestone 48 Limestone 35 Limestone 54 Limestone 48 Dolomite 47 Dolomite better than satisfactory. This can be explained on the one hand by much smaller in situ UCS values for the rocks of the outcrops and on the other hand by the high ratio of partings in the rock mass reducing its rock strength. Carbonates in the studied outcrops suffered from deformation caused by several stress fields (Fodor 1988; Csontos 1999; Kozák et al. 2001; Németh 2005; McIntosh 2014). Signs of strong deformation are clearly visible in both the outcrops and the texture of the rocks revealed by microscopic analyses (Pelikán 2005). Strong shearing is indicated by sigma clasts enclosed in the orientated texture (Fig. 2) of a rock sample. Twin lamina of calcite crystals (Fig. 3) also indicate that pressure was applied on the rock while calcite veins crossing each other and the orientated texture suggest that multiple stress fields deformed the rock sample. Strong deformation with multiple stages and directions increases the number of partings in the rock mass and reduces UCS. As a result good qualification was not achieved by either rock masses of the studied outcrops. Even is the most compact rock masses appears a large fault with clayey slickenside (Fig. 4) or a joint (Fig. 5). Table 2 reveals that rock masses with best qualification belong not to one formation. Similarly outcrops with poorest qualification expose the rock masses of different formations. Based on the results the RMR qualification of rock masses is not dependent on formations. RMR values vary in wide range even within one rock formation. For example, one outcrop exposing Hámor Dolomite Formation scored 16 points while another scored 48 points. Similarly rock masses of Ablakoskővölgy Formation are exposed in outcrops scoring 31 points and 58 points as well. Therefore Landscape & Environment 10 (3-4) Fig. 2. Sigma clasts in strongly orientated texture in the rocks of Ablakoskővölgy Formation (II N) Fig. 3. Calcite crystal with twin lamina and calcite filled veins crossing the orientated texture in Gerennavár Limestone near Ómassa (II N) RMR qualification of outcrops depends on local conditions, however, it shows spatial regularities. In Figure 6 rock masses in areas marked by green rectangles and circle (marked as 1, 2 and 3) are stable having relatively high strength in the study area and qualified as satisfactory. In contrast, areas enclosed by red rectangles (marked as 4 and 5) and two outcrops (Borovnyák 18, Ómassa-1) have the poorest RMR qualification. Areas with best qualification are located in the northern edge (area marked as 1) and southern margin (marked as 3) of Nyárjú Hill and along the ridge trending NW SE running into Ómassa. Areas and outcrops with poorest qualification can be found in the Garadna Valley (and in its northern continuation, the Száraz Valley) at places where tributary valleys join the main valley trending E W (area marked as 4 and outcrop Ómassa-1) or where particularly weak zones with strongly fractured, deformation and brecciated rocks occur (outcrop Borovnyák 18 and the area marked as 5). Both the Garadna Valley and the Száraz Valley were formed along major fractures and the smaller tributary valleys also represent fractures. Rocks are most deformed and fractured at places where fractures and joints cross each other (Kozák et al. 2001; McIntosh 2014). Outcrop Borovnyák 18 with the poorest rock mass is located at the eastern termination of the main mass of Nyárjú Hill (at the intersection of the N-S trending Angyal Valley and the Száraz Valley) where it meets the ridge of Borovnyák-tető running towards NE. In the transition zone between the two ridges at the intersection of two structural lines represented by two valleys the rock mass with strongest deformation and greatest volume of parting and also with small UCS and thus with very small RMR value (Table 2) can be found (Fig. 6). Fig. 4. Clay filled fault in Hámor Dolomite outcrop near Ómassa 166 Landscape & Environment 10 (3-4) Fig. 5. Rock mass with united appearance near Bánkút (Nagyvisnyó Limestone Formation) Fig. 6. Spatial distribution of rock mass having higher and smaller strength in the valley head of Garadna Valley in the vicinity of Bánkút and Ómassa Landscape & Environment 10 (3-4) Outcrop Ómassa-1 is located at the intersection of the Garadna Valley and one of its tributary valleys (Fig. 6), i.e. at the intersection of two joints where the rock mass is strongly fractured and brecciated thus showing high volume of partings. Area 5 is found on a steep valley side where ravines developed. Two springs also appear in this area that drive water down into the Garadna Valley every now and again. Opposite this zone of weakness on the northern side of Ómassa Farkas-nyak Valley joins the Garadna Valley suggesting that this area is also located at the intersection of two major structural lines. 4. Conclusions Based on the RMR evaluation of 29 outcrops in the Bükk Mts. the following conclusions can be made: The 6 parameters including UCS, RQD value, parting distances, state of parting surfaces, presence of water and the orientation of partings can be applied successfully in describing the strength of natural rock mass; RMR scores of outcrops do not depend on the formation the rocks of which are exposed by the outcrop; RMR qualification shows relationship with morphology. Outcrops with highest RMR score are located in united morphological elements composed of compact and less deformed rock mass. Outcrops with poorest qualification are located in zones of strongest deformation, generally at the intersection of major fractures or structural lines occurring in the form of intersecting valleys in the morphology. Acknowledgements Research work of Balázs Encs was supported by DETEP programme at the University of Debrecen. Authors express their thank to Tamás Debreczeni, Tamás Juhász, Lajos Nagy, Tibor Perge and Bence Sohajda for their help in fieldwork. 5. References 167 Bieniawski, Z.T. (1973): Engineering classification of jointed rock masses. Trans. S. African Institute of civil engineers. 15(12): Birot, P. (1958): Morphologie Structurale. Presses Univers, Paris. Csontos L. (1999): A Bükk hegység szerkezetének főbb vonásai. Földtani Közlöny. 129(4): Deere, D.U. (1969): Geological considerations. In: Stagg, K.G. Zienkiewicz, O.C. (Eds.)(1969): Rock mechanics in engineering practice Demeter, G. Szabó, Sz. (2008a): Identifying lithological features using morphometric parameters derived from DEM. Acta GGM Debrecina Geology, Geomorphology and Physical Geography Series. 3: Demeter, G. Szabó, Sz. (2008b): Morfometriai és litológiai tényezők kapcsolatának kvantitatív vizsgálata a Bükkben és északi előterén: A statisztikus felszínelemzés alkalmazásának lehetőségei a geomorfológiában. Kossuth Egyetemi Kiadó, Debrecen, Fodor L. (1988): Többfázisú redőképződés a Bükkhegységi Nagy Ökrös környékén. Földtani Közlöny. 118(1): Gálos, M. Vásárhelyi, B. (2006): Kőzettestek osztályozása az építőmérnöki gyakorlatban. Műszaki Egyetemi Könyvkiadó, Budapest. Gerasimov, I.P. (1946): Experience with geomorphological interpretation of the general scheme of geological structure of URSS. Probleme Fizische Geographie. 12: Kozák, M. Püspöki, Z. McIntosh, R.W. (2001): Structural Development Outline of the Bükk Mountains Reflecting Recent Regional Studies. Acta Geographica, Geologica ac Meteorologica Debrecina. 35: McIntosh, R.W. (2014): A Bükkium morfotektonikája. Kézirat, PhD értekezés. Debreceni Egyetem, Debrecen. Németh N. (2005): A DK-i Bükk keleti részének szerkezetföldtani viszonyai. PhD értekezés, Miskolci Egyetem Pelikán, P. (2005): A Bükk hegység földtana, Magyarázó a Bükk-hegység földtani térképéhez (1:50000). MÁFI kiadvány Püspöki, Z. Szabó, Sz. Demeter, G. Szalai, K. McIntosh, R.W. Vincze, L. Németh, G. (2005): Statistical relationship between lithological characteristics and morphological factors an example for statistical surface analysis. Geomorphology. 71: 168 Landscape & Environment 10 (3-4) Scheidegger, A.E. (1980): The orientation of valley trends in Ontario. Zeitschrift für Geomorphologie N.F. 24(1): Scheidegger, A.E. (2001): Surface joint systems, tectonic stresses and geomorphology: a reconciliation of conflicting observations. Geomorphology. 38: Selby, M.J. (1980): A rock mass strength classification for geomorphic purposes with tests from Antarctica and New Zealand. Zeitschrift für Geomorphologie N.F. 24(1): Telbisz, T. (1999): Computer simulation in geomorphology. Bulletin of the Hungarian Geographical Society Török, Á. (2007): Geológia mérnököknek. Műegyetem Kiadó, Budapest. ISBN Twidale, C.R. (1971): Structural Landforms. The M.I.T. Press, London
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