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Effect of the specimen length on ultrasonic P-wave velocity in some volcanic rocks and limestones
Journal of African Earth Sciences 112 (2015) 142e149
Contents lists available at ScienceDirect
Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci
Effect of the specimen length on ultrasonic P-wave velocity in some volcanic rocks and limestones Kadir Karaman a, Ayberk Kaya b, *, Ayhan Kesimal a a b
Karadeniz Technical University, Faculty of Engineering Department of Mining Engineering, 61080, Trabzon, Turkey Recep Tayyip Erdogan University, Faculty of Engineering Department of Geological Engineering, 53100, Rize, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 July 2015 Received in revised form 20 September 2015 Accepted 21 September 2015 Available online 25 September 2015
Ultrasonic P-wave velocity (UPV) is commonly used in different fields such as civil, mining, geotechnical, and rock engineering. One of the significant parameters which affect the UPV of rock materials is likely to be the length of test cores although it is not mentioned in the literature. In this study, in order to explore the influence of the specimen length on the UPV, rock samples were collected from eight different locations in Turkey. The NX-sized core specimens having different length of 50, 75, 100, 125, and 150 mm were prepared. Before the analyses, rocks were divided into two groups in terms of their geological origins such as volcanic and chemical sedimentary (limestone) rocks. The UPV tests were carried out under dry and saturated conditions for each 200 core specimens. By evaluating the test results, it was shown that the length of the specimens significantly affects the UPV values. Based on the regression analyses, a method was developed to determine the threshold specimen length of studied rocks. Fluctuations in UPVdry and UPVsat values were generally observed for cores smaller than the threshold specimen length. In this study, the threshold specimen length was determined as 79 mm for volcanic rocks and 109 mm for limestones. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Ultrasonic P-wave velocity Threshold specimen length Volcanic rocks Limestones
1. Introduction Determination of the engineering characteristics of rocks is considered to be among the most significant components in geoengineering projects. One of the ultrasonic techniques, UPV, has been widely used physical parameter of rocks which is determined both in the laboratory and on-site. It is destructiveness and simple to perform, which is why it has been used for many years in civil, mining and geotechnical engineering such as quarrying, rock slopes, underground opening, blasting and ripping. The UPV is affected by many factors such as lithology, unit weight, grain shape and size, anisotropy, porosity, degree of saturation, weathering and alteration, confining pressure, temperature, and discontinuity properties (roughness, filling material, orientation, etc.). Additionally, the shape and size of the samples may affect the UPV (Vasconcelos et al., 2008; Fener, 2011). Most researchers have investigated the relationships between the UPV and engineering properties of rocks (uniaxial compressive
* Corresponding author. E-mail addresses: [email protected] (K. Karaman), erdogan.edu.tr (A. Kaya), [email protected] (A. Kesimal). http://dx.doi.org/10.1016/j.jafrearsci.2015.09.017 1464-343X/© 2015 Elsevier Ltd. All rights reserved.
ayberk.kaya@
and tensile strengths, Schmidt rebound hardness, Poisson's ratio, modulus of elasticity, porosity, unit weight, etc.). They obtained that UPV is closely related with properties of rock (e.g. Tugrul and Zarif, 1999; Yasar and Erdogan, 2004; Kahraman, 2007; Sharma and Singh, 2008; Yagiz, 2011; Khandelwal, 2013; Aydin, 2014). A number of authors reported that it has been used for a variety of other specific fields such as the assessment of grouting (Knill, 1970; Turk and Dearman, 1987), rock bolt reinforcement (Price et al., 1970), efficiencies of blasting in the rock mass (Young et al., 1985), the estimation of strength and deformation of rock mass (Gladwin, 1982), the weathering degree rock (Karpuz and Pasamehmetoglu, 1997), fractured rock mass characterization (Kahraman, 2002), and thermal conductivity of rocks (Ozkahraman et al., 2004). UPV is also used in seismic, seismology and in petroleum geosciences (Ikelle and Amundsen, 2005). The effect of saturation and porosity on the sound velocities was studied by some researchers. Thill and Bur (1969) researched the effect of water saturation on sound velocity for granodiorite. The authors indicated the UPV changes considerably with porosity and degree of saturation although intact rock has only a minute amount of porosity. Ramana and Venkatanarayana (1973) reported that both weight and UPV of the samples increased with increasing
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Fig. 1. The map showing sampling locations.
time of saturation for sedimentary rocks. Lama and Vutukuri (1978) indicated the UPV increased as the degree of saturation increased. Vasconcelos et al. (2008) correlated the UPV with pysicomechanical (uniaxial compressive and tensile strengths, porosity and unit weight) and elastic (Young's modulus) properties of granites. They used the cylindrical specimens (diameter: 75 mm, length: 150 mm) for uniaxial compressive tests and prismatic specimens (40 50 80 mm3) for tensile tests. They considered that the size of samples utilized in the tensile tests were too small for the UPV measurements of coarse-grained granites. Thus, they also performed the UPV measurements in cubic specimens (150 150 150 mm3) used in the porosity tests. Fener (2011) investigated the effect of the specimen diameter on the UPV in laboratory. He performed the UPV measurements on the core specimens having different diameters (the smallest core diameter is 29.68 mm and the largest one is 113.50 mm) and the core specimens have the same length. He found exponential and polynomial relationship between the specimen diameters and UPV. The author stated that a remarkable increase in the UPV was shown for the specimens having largest diameter; however some groups show a decrease in UPV based on the increase in diameter of core sample. Since the researchers prefer to perform the UPV and other rock mechanics tests on same specimens, the length of the specimens are chosen according to the standards or suggested methods. For example, according to the ISRM (2007) suggested method to determine the uniaxial compressive strength (UCS), the test samples shall be right circular cylinders having a length to diameter ratio of 2.5e3.0 and a diameter preferentially of not less than NXsized core, roughly 54.7 mm. Further, before testing the UCS, UPV
test is generally measured on the same core specimens. Thus, the rock specimens having a non-standard length are ignored in tests based on the suggested methods. However, more reliable correlations may be obtained by adding the rock specimens having an threshold specimen length even if the non-standard lengths are used for only UPV testing. In relevant literature published around the world, no study has been carried out to investigate the effect of the core sample length on the UPV in intact rocks. In this study, it is hence aimed to investigate the effect of core sample length on the UPV in volcanic rocks and limestones, exploring the threshold specimen length. 2. Material and method 2.1. Sampling Eight rock types were sampled and rock blocks were collected from different locations in Trabzon, Giresun, Gumushane, Amasya, and Mugla regions of Turkey (Fig. 1, Table 1), four of which are volcanic rocks and four are limestones. Block samples used in this study were controlled for macroscopic imperfections such as cracks and weathering in order to that it might provide standard testing samples. As the anisotropic characteristics of rocks directly affect the ultrasonic P-wave velocity (Piniska, 1977) in this study, the rock types with free of anisotropy which are considered to be homogenous were preferred. No anisotropic rocks having schistosity, foliation and bedding plane were chosen to evaluate. Volcanic rock and limestone specimens were collected from the lithologically massive formations. Another significant factor that influences the UPV is the grain
Table 1 The location and lithology of rocks sampled. Rock code
Rock class
Rock Type
Lithology
Location
1 2 3 4 5 6 7 8
Igneous Igneous Igneous Igneous Sedimentary Sedimentary Sedimentary Sedimentary
Volcanic Volcanic Volcanic Volcanic Chemical Chemical Chemical Chemical
Andesite Basalt Vesicular basalt Dacite Beige limestone White limestone Black limestone Grey limestone
Trabzon/Arakli Giresun/Gorele Trabzon/Center Giresun/Tirebolu Amasya/Gumushacikoy Mugla/Yatagan Duzce/Akcakoca Gumushane/Torul
1.70 1.98 9.76 0.75 0.29 0.15 0.20 0.50
150 mm 125 mm 100 mm
1.45 1.85 9.75 0.82 0.31 0.25 0.22 0.52 1.48 1.72 9.70 0.95 0.27 0.20 0.20 0.52
75 mm 50 mm
1.83 2.22 9.40 1.62 0.26 0.24 0.26 0.58 4750 4495 2798 5035 4632 5179 5147 3475
150 mm 125 mm
4733 4317 3294 5163 4579 5348 5200 4310 4772 4591 3603 5629 4643 4989 5399 4002
100 mm 75 mm
4701 4590 3959 5515 3874 3739 4589 3137
50 mm
3853 3282 3237 5224 3312 3439 4272 2227 4036 3842 3332 4386 3228 4283 4684 2852
150 mm 125 mm 100 mm
Andesite Basalt Vesicular basalt Dacite Beige limestone White limestone Black limestone Grey limestone 1 2 3 4 5 6 7 8
75 mm
4024 3734 3372 4308 3288 4381 4693 2798
50 mm
3796 3670 3390 4549 3292 4134 4544 2583
Average napp (%) Average UPVsat (m/s) Average UPVdry (m/s) Test number Lithology Rock code
Table 2 The average UPVdry, UPVsat, and napp values of rock samples.
The NX-sized core specimens used in the experimental studies were obtained from blocks to the required dimension using core drilling machine. The ends of the samples were machined for flat ground and made parallel to each other. The cut end faces of the core samples were smoothened to maintain precision of within ±0.02 mm and made perpendicular to within ±0.05 mm to the core axis using comparator. After a macroscopical checking, only unweathered, homogeneous, and free of visible joint specimens were considered. In order to obtain the exact results as well as the best comparison, the experiments were carried out under the same conditions. Core specimens were prepared at five different lengths with the same diameter for each rock type. The core length for the smallest specimen is 50 mm and 150 mm for the longest specimen. The core diameters are the same (NX: 54.7 mm) in order to minimize the interaction between the UPV and the core diameter. The UPV testing applied on the dry and saturated specimens. Ultrasonic pulse method for the UPV testing was performed using the Pundit-plus model equipment. An accuracy of 0.1 mm for the length of the measuring base was used. Before the measurements, the cut ends of samples were polished to provide flat and smooth surface. A thin film of petroleum jelly (vaseline) was fulfilled to the surface of the transducers (receiver and transmitter) so as to provide full contact and to remove the air gap between transducers and the specimen surface. In the laboratory, direct, semidirect and indirect methods could be performed for UPV measurement. The direct procedure known to be the most reliable and satisfactory method, was performed during the test in order that the receiver and transmitter might be positioned on the opposite cut end surfaces of the samples used. In the tests, the ultrasonic pulse time was measured with an accuracy of 0.1 ms. The UPV was obtained by dividing the length of the NX-sized core and the travel pulse time. Mean UPV value was obtained by averaging the P-wave values of five tests on the same lithology type. A total of 200 core specimens having different lengths were used in the experiments. Core specimens used for UPV measurement were also evaluated in the calculation of apparent porosity. The sample volume was determined from an average of three caliper readings. Samples were saturated with distilled water at room temperature for 24 h. Achieving 100% saturation is theoretically impossible for homogeneous rocks apart from the clastic rocks due to unconnected voids in their structures. However, the assumption of 100% saturation is made after 24/48 h in distilled water for homogeneous volcanic, plutonic rocks and limestones which have apparent porosity (e.g. Sharma and Singh, 2008; Fener, 2011; Karaman and Kesimal, 2015; Kaya and Karaman, 2015; Karaman et al., 2015). After the saturated core specimens were performed for UPV tests, weight of each specimen was calculated. The dry weight of samples was defined after drying for 24 h at a temperature of 105 C in oven. The values of apparent porosity were obtained using saturation and caliper techniques. The volume of pores was determined from dry and saturated weights. Apparent porosity values of each sample were derived from the ratio of the void volumes to the sample volume. All tests were implemented based
3705 3682 3174 4377 2870 2983 4042 2237
2.2. Experimental procedures
3235 2502 2469 4029 2417 2195 3850 1700
size of the minerals. The travel length of the pulse though the rock samples shall be at least 10 times the mean grain size based on the ISRM (2014) suggested methods. For this reason, volcanic (extrusive) rocks with aphanitic textures (micro minerals are distributed in matrix) and limestones with micritic matrixs were used for experimental studies to provide required sample lengths.
1.47 1.72 10.60 0.97 0.30 0.18 0.30 0.55
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25 25 25 25 25 25 25 25
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on the ISRM (2007) suggested methods, and results of all experimental studies were given in Table 2. 2.3. Evaluation of the test results Evaluation of the data obtained from laboratory studies were performed in two stages. In first stage, the relationships between ultrasonic P-wave velocities under dry and saturated conditions (UPVdry and UPVsat) and apparent porosity (napp %) were investigated using regression analyses for each length. Therefore, the regression lines/curves were drawn for the UPVdry-UPVsat and UPVdry-napp data pairs belong to volcanic rocks and limestones studied. Since porosity is directly affecting the UPV, this parameter is used in the regression analyses. In second stage, the threshold specimen lengths of the NX-sized volcanic rocks and limestones were determined according to the UPV values. The detailed information about this method was given in later stages. 3. Results and discussion 3.1. Results The regression analyses were performed for each specimen
145
length varies between 50 and 150 mm. As shown in Fig. 2, the UPV values obtained from dry and saturated specimens are well correlated and two different trends were observed for volcanic rocks and limestones. The equations of the best-fit lines and the correlation coefficients (r) were determined for each regression. Strong relationships (r: 0.81e0.99) were obtained for the UPVdry and UPVsat. Kahraman (2007) correlated the UPVdry and UPVsat. for all rocks, igneous, metamorphic and sedimentary rocks with different porosity values (lower and higher than 1%). The UPVdry was also correlated with the apparent porosity (napp %). The rocks were classified into two groups based on their geological origins such as volcanic and chemical sedimentary (limestones). The vesicular basalt exhibits a different distribution unlike other volcanic rocks due to its high porosity values (Fig. 3). Therefore, lower UPV for the vesicular basalt was obtained compared to other rocks studied. Since number of rocks having high porosity values is insufficient in this study, the correlation coefficient (r) will not reliable for vesicular basalt. Thus, it was not taken into account in the regression analyses. Significant relationships were found among the parameters, and two different trends were seen for the volcanic rocks and limestones. There is a big difference between the two trends. Limestones follow a more steeply trend line than that of volcanic rocks. The different trend is likely to be related to the apparent porosity of limestones rocks that limited to a narrower range.
Fig. 2. UPVdry of the volcanic rocks and limestones in correlation with UPVsat.
146
K. Karaman et al. / Journal of African Earth Sciences 112 (2015) 142e149
Sound velocity of dry rock specimens decreased with the increase of porosity. The average UPVdry and UPVsat values against specimen length were plotted for each rock lithology (Figs. 4 and 5). As shown in the figures, the UPVdry and UPVsat were remained constant or decreased (or at least fluctuate closely around a constant mean value) for NX-sized cores over the threshold length. In order to predict the threshold specimen length for a consistent UPV value, a method was developed. This method was carried out in two steps. Firstly, UPVdry-Sample length and UPVsat-Sample length data pairs belong to the volcanic rocks and limestones were correlated using regression analyses. Secondly, two regression lines were fitted to the data set; one is an inclined line fitted to the UPVdry and UPVsat values increasing with specimen length; the other is a nearly horizontal line fitted to UPVdry data and negative inclined line fitted to the UPVsat data, showing no or little changes with specimen length. It was considered that the value at the intersection point of two regression lines for each lithology is threshold specimen length value (Figs. 4 and 5). In Table 3, threshold specimen lengths are nearly same for both dry and saturated conditions. Therefore, threshold lengths of core specimens for the some volcanic rocks and limestones were determined by averaging their related values. The average threshold specimen lengths were given
in Table 3. From the table, the threshold specimen lengths were obtained as 79 and 109 mm for volcanic rocks and limestones, respectively. Based on the results of this study, the UPVdry and UPVsat values were approximately remained constant or decreased for cores having a length over the 75 mm for the volcanic rocks and 100 mm for the limestones. In the saturated UPV values, it was obtained higher decrease than the dry UPV values over the threshold specimen lengths usually in vesicular basalt and grey limestone specimens. 3.2. Discussion In the literature, there is a great deal of research exploring the effect of specimen size on the UCS (e.g. Thuro et al., 2001; ASTM, 2002; ISRM, 2007; Tuncay and Hasancebi, 2009; Darlington et al., 2011) and on Schmidt rebound hardness of rocks (e.g. ASTM, 2005b; ISRM, 2007; Demirdag et al., 2009). As for the UPV, ASTM (2005a) published a graph showing values of specimen diameter (in.), specimen length (in.) and average grain size versus the ratio of compression propagation velocity to resonance frequency. Whereas, the lateral minimum dimension is suggested to be not less than 10 times the wave-length based on the ISRM (2014). In addition to this, the travel distance of the pulse through the rock
Fig. 3. UPVdry of the volcanic rocks and limestones in correlation with napp.
K. Karaman et al. / Journal of African Earth Sciences 112 (2015) 142e149
sample shall be at least 10 times the mean grain size. However, it was commonly known that the length to diameter ratios varying from 2 to 3 were generally used by appliers in practice for UPV testing without determining the average grain size of the specimen. Therefore, this study could have made a significant contribution to practical solution of the UPV experiments especially for the some volcanic rocks and limestones. However, the length effect on intrusive rocks (granite, diorite, etc.) may be different from that on volcanic rocks and limestones; this should be further examined. 4. Conclusion In this study, NX-sized cores having lengths between 50 and
147
150 mm were evaluated to investigate the specimen length on the UPV. According to the findings derived from the present study, the main results were presented below; 1) The UPVdry-UPVsat and UPVdry-napp data pairs were correlated using regression analyses. Significant relationships were found among the parameters for the volcanic rocks and limestones. Two different trends were observed for those rock groups according to the regression analyses. Limestones followed a more steeply sloped line than that of volcanic rocks. 2) UPV values versus specimen length were plotted for all rocks. Core specimens having lengths 50 mm and 75 mm, an increase in the UPV values based on an increase in length was shown for
Fig. 4. Method for threshold specimen length determination for volcanic rocks and limestones using average UPVdry values.
148
K. Karaman et al. / Journal of African Earth Sciences 112 (2015) 142e149
Fig. 5. Method for threshold specimen length determination for volcanic rocks and limestones using average UPVsat values.
the volcanics. Further, a significant increase in the UPV was obtained for limestone specimens having lengths 50 mm, 75 mm and 100 mm. Over the length of 75 mm for the volcanic rocks and 100 mm for the limestones, higher decreasing on UPV values was seen. This study showed that both the UPVdry and UPVsat are strongly contingent upon the variation of the specimen length. 3) According to the results of the statistical analyses, threshold specimen length for the volcanic rocks and limestones were determined as 79 and 109 mm, respectively. UPVdry values were remained constant or at least fluctuate closely around a constant mean value for NX-sized cores over the threshold
specimen length. However, UPVsat values were tended to decrease over the critical core specimen length for some rocks (vesicular basalt and grey limestone). These results rendered the UPV measurements unnecessary for the core samples over the length of 79 and 109 mm for the volcanic rocks and limestones, respectively. 4) Threshold specimen length was tried to predict for some rocks studied (i.e. volcanics and limestones). However, this only goes for the eight types of rock used and additional research on different rock types are needed especially for intrusive and metamorphic rocks as well as anisotropic rocks.
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Table 3 The threshold specimen length for volcanic rocks and limestones according to average UPVdry and UPVsat values. Rock code
Lithology
1 2 3 4
Andesite Basalt Vesicular basalt Dacite
5 6 7 8
Beige limestone White limestone Black limestone Grey limestone
a b
Threshold specimen length for each rock lithology (mm) According to average UPVdry
According to average UPVsat
76 73 83 85 79a 104 109 115 104 108b
76 75 76 87 79a 104 119 98 117 110b
Threshold specimen length for volcanic rocks. Threshold specimen length for limestones.
Acknowledgments Authors would like to express their sincerest gratitude to the editor and reviewers for their excellent comments. Also thanks to Dr. Bayram Ercikdi for improving paper quality and English editing of the text. References ASTM, 2002. Standard Test Method for Unconfined Compressive Strength of Intact Rock Core Specimens. American Society for Testing and Materials, 29388eD3005. ASTM, 2005b. Standard Test Method for Laboratory Determination of Pulse Velocities and Ultrasonic Elastic Constants of Rock. American Society for Testing and Materials, pp. D 2845e2905. ASTM, 2005a. Standard Test Method for Determination of Rock Hardness by Rebound Hammer Method. American Society for Testing and Materials, pp. D 5873e5905. Aydin, A., 2014. Upgraded ISRM suggested method for determining sound velocity by ultrasonic pulse transmission technique. Rock Mech. Rock Eng. 47, 255e259. Darlington, W.J., Ranjith, P.G., Choi, S.K., 2011. The effect of specimen size on strength and other properties in laboratory testing of rock and rock-like cementitious brittle materials. Rock Mech. Rock Eng. 44, 513e529. Demirdag, S., Yavuz, H., Altindag, R., 2009. The effect of sample size on Schmidt rebound hardness value of rocks. Int. J. Rock Mech. Min. Sci. 46, 725e730. Fener, M., 2011. The effect of rock specimen dimension on the P-wave velocity. J. Non Eva 30, 99e105. Gladwin, M.T., 1982. Ultrasonic stress monitoring in underground mining. Int. J. Rock Mech. Min. Sci. 19, 221e228. Ikelle, L., Amundsen, L., 2005. Introduction to Petroleum Seismology. Investigations in Geophysics Series No. 12. Society of Exploration Geophysicists, USA. ISRM, 2007. The complete ISRM suggested methods for rock characterization, testing and monitoring: 1974e2006. In: Ulusay, R., Hudson, J.A. (Eds.), Suggested Methods Prepared by the Commission on Testing Methods. Compilation arranged by the ISRM Turkish National Group, ISRM, Ankara. ISRM, 2014. The ISRM suggested methods for rock characterization, testing and monitoring: 2007-2014. In: Ulusay, R. (Ed.), Suggested Methods Prepared by the Commission on Testing Methods. International Society for Rock Mechanics, Springer. Kahraman, S., 2002. The effects of fracture roughness on P-wave velocity. Eng. Geol. 63, 347e350. Kahraman, S., 2007. The correlations between the saturated and dry P-wave velocity of rocks. Ultr 46, 341e348. Karaman, K., Kesimal, A., 2015. Evaluation of the influence of porosity on the engineering properties of volcanic rocks from the Eastern Black Sea Region: NE Turkey. Arab. J. Geosci. 8, 557e564. Karaman, K., Kaya, A., Kesimal, A., 2015. Use of the point load index in estimation of
the strength rating for the RMR system. J. Afr. Ear. Sci. 106, 40e49. Karpuz, C., Pasamehmetoglu, A.G., 1997. Field characterization of weathered Ankara andesites. Eng. Geol. 46, 1e17. Kaya, A., Karaman, K., 2015. Utilizing the strength conversion factor in the estimation of uniaxial compressive strength from the point load index. Bull. Eng. Geol. En. http://dx.doi.org/10.1007/s10064-015-0721-1. Khandelwal, M., 2013. Correlating P-wave velocity with the physico-mechanical properties of different rocks. Pure Appl. Geophys. 170, 507e514. Knill, T.L., 1970. The application of seismic methods in the interpretation of grout takes in rock. In: Proceedings of the Conference on In-situ Investigation in Soils and Rocks. Bri Geo Soc, vol. 8, pp. 93e100. Lama, R.D., Vutukuri, V.S., 1978. Handbook on Mechanical Properties of Rocks, vol. 2. Trans Tech Publications, Clausthal, Germany. Ozkahraman, H.T., Selver, R., Isik, E.C., 2004. Determination of the thermal conductivity of rock from P-wave velocity. Int. J. Rock Mech. Min. Sci. 41, 703e708. Piniska, J., 1977. Correlation between mechanical and acoustic properties of flysch sandstones. Proc. Int. Symp. Geo. Ita. Capri 1, 387e394. Price, D.G., Malone, A.W., Knill, T.L., 1970. The application of seismic methods in the design of rock bolt system. In: Proceedings of the First International Congress. Int Assoc Eng Geol, vol. 2, pp. 740e752. Ramana, Y.V., Venkatanarayana, B., 1973. Laboratory studies on Kolar rocks. Int. J. Rock Mech. Min. Sci. Geo. Abst. 10, 465e489. Sharma, P.K., Singh, T.N., 2008. A correlation between P-wave velocity, impact strength index, slake durability index and uniaxial compressive strength. Bull. Eng. Geol. En. 67, 17e22. Thill, R.E., Bur, T.R., 1969. An automated ultrasonic pulse measurement system. Geo 34, 101e105. Thuro, K., Plinninger, R.J., Zah, S., Schutz, S., 2001. Scale effects in rock strength properties. Part 1: unconfined compressive test and Brazilian test. In: Proceedings of the ISRM Regional Symposium EUROCK, Espoo, Finland, pp. 169e174. Tugrul, A., Zarif, I.H., 1999. Correlation of mineralogical and textural characteristics with engineering properties of selected granitic rocks from Turkey. Eng. Geol. 51, 303e317. Tuncay, E., Hasancebi, N., 2009. The effect of length to diameter ratio of test specimens on the uniaxial compressive strength of rock. Bull. Eng. Geol. En. 68, 491e497. Turk, N., Dearman, W.R., 1987. Assessment of grouting efficiency in a rock mass in terms of seismic velocities. Bull. Int. Assoc. Eng. Geol. 36, 101e108. Vasconcelos, G., Lourenco, P.B., Alves, C.A.S., Pamplona, J., 2008. Ultrasonic evaluation of the physical and mechanical properties of granites. Ult 48, 453e466. Yagiz, S., 2011. P-wave velocity test for assessment of geotechnical properties of some rock materials. Bull. Mat. Sci. 34, 947e953. Yasar, E., Erdogan, Y., 2004. Correlating sound velocity with density, compressive strength and Young's modulus of carbonate rocks. Int. J Rock Mech. Min. Sci. 41 (5), 871e875. Young, R.P., Hill, T.T., Bryan, I.R., Middleton, R., 1985. Seismic spectroscopy in fracture characterization. Q. J. Eng. Geol. Hydroge. 18, 459e547.
Contents lists available at ScienceDirect
Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci
Effect of the specimen length on ultrasonic P-wave velocity in some volcanic rocks and limestones Kadir Karaman a, Ayberk Kaya b, *, Ayhan Kesimal a a b
Karadeniz Technical University, Faculty of Engineering Department of Mining Engineering, 61080, Trabzon, Turkey Recep Tayyip Erdogan University, Faculty of Engineering Department of Geological Engineering, 53100, Rize, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 July 2015 Received in revised form 20 September 2015 Accepted 21 September 2015 Available online 25 September 2015
Ultrasonic P-wave velocity (UPV) is commonly used in different fields such as civil, mining, geotechnical, and rock engineering. One of the significant parameters which affect the UPV of rock materials is likely to be the length of test cores although it is not mentioned in the literature. In this study, in order to explore the influence of the specimen length on the UPV, rock samples were collected from eight different locations in Turkey. The NX-sized core specimens having different length of 50, 75, 100, 125, and 150 mm were prepared. Before the analyses, rocks were divided into two groups in terms of their geological origins such as volcanic and chemical sedimentary (limestone) rocks. The UPV tests were carried out under dry and saturated conditions for each 200 core specimens. By evaluating the test results, it was shown that the length of the specimens significantly affects the UPV values. Based on the regression analyses, a method was developed to determine the threshold specimen length of studied rocks. Fluctuations in UPVdry and UPVsat values were generally observed for cores smaller than the threshold specimen length. In this study, the threshold specimen length was determined as 79 mm for volcanic rocks and 109 mm for limestones. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Ultrasonic P-wave velocity Threshold specimen length Volcanic rocks Limestones
1. Introduction Determination of the engineering characteristics of rocks is considered to be among the most significant components in geoengineering projects. One of the ultrasonic techniques, UPV, has been widely used physical parameter of rocks which is determined both in the laboratory and on-site. It is destructiveness and simple to perform, which is why it has been used for many years in civil, mining and geotechnical engineering such as quarrying, rock slopes, underground opening, blasting and ripping. The UPV is affected by many factors such as lithology, unit weight, grain shape and size, anisotropy, porosity, degree of saturation, weathering and alteration, confining pressure, temperature, and discontinuity properties (roughness, filling material, orientation, etc.). Additionally, the shape and size of the samples may affect the UPV (Vasconcelos et al., 2008; Fener, 2011). Most researchers have investigated the relationships between the UPV and engineering properties of rocks (uniaxial compressive
* Corresponding author. E-mail addresses: [email protected] (K. Karaman), erdogan.edu.tr (A. Kaya), [email protected] (A. Kesimal). http://dx.doi.org/10.1016/j.jafrearsci.2015.09.017 1464-343X/© 2015 Elsevier Ltd. All rights reserved.
ayberk.kaya@
and tensile strengths, Schmidt rebound hardness, Poisson's ratio, modulus of elasticity, porosity, unit weight, etc.). They obtained that UPV is closely related with properties of rock (e.g. Tugrul and Zarif, 1999; Yasar and Erdogan, 2004; Kahraman, 2007; Sharma and Singh, 2008; Yagiz, 2011; Khandelwal, 2013; Aydin, 2014). A number of authors reported that it has been used for a variety of other specific fields such as the assessment of grouting (Knill, 1970; Turk and Dearman, 1987), rock bolt reinforcement (Price et al., 1970), efficiencies of blasting in the rock mass (Young et al., 1985), the estimation of strength and deformation of rock mass (Gladwin, 1982), the weathering degree rock (Karpuz and Pasamehmetoglu, 1997), fractured rock mass characterization (Kahraman, 2002), and thermal conductivity of rocks (Ozkahraman et al., 2004). UPV is also used in seismic, seismology and in petroleum geosciences (Ikelle and Amundsen, 2005). The effect of saturation and porosity on the sound velocities was studied by some researchers. Thill and Bur (1969) researched the effect of water saturation on sound velocity for granodiorite. The authors indicated the UPV changes considerably with porosity and degree of saturation although intact rock has only a minute amount of porosity. Ramana and Venkatanarayana (1973) reported that both weight and UPV of the samples increased with increasing
K. Karaman et al. / Journal of African Earth Sciences 112 (2015) 142e149
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Fig. 1. The map showing sampling locations.
time of saturation for sedimentary rocks. Lama and Vutukuri (1978) indicated the UPV increased as the degree of saturation increased. Vasconcelos et al. (2008) correlated the UPV with pysicomechanical (uniaxial compressive and tensile strengths, porosity and unit weight) and elastic (Young's modulus) properties of granites. They used the cylindrical specimens (diameter: 75 mm, length: 150 mm) for uniaxial compressive tests and prismatic specimens (40 50 80 mm3) for tensile tests. They considered that the size of samples utilized in the tensile tests were too small for the UPV measurements of coarse-grained granites. Thus, they also performed the UPV measurements in cubic specimens (150 150 150 mm3) used in the porosity tests. Fener (2011) investigated the effect of the specimen diameter on the UPV in laboratory. He performed the UPV measurements on the core specimens having different diameters (the smallest core diameter is 29.68 mm and the largest one is 113.50 mm) and the core specimens have the same length. He found exponential and polynomial relationship between the specimen diameters and UPV. The author stated that a remarkable increase in the UPV was shown for the specimens having largest diameter; however some groups show a decrease in UPV based on the increase in diameter of core sample. Since the researchers prefer to perform the UPV and other rock mechanics tests on same specimens, the length of the specimens are chosen according to the standards or suggested methods. For example, according to the ISRM (2007) suggested method to determine the uniaxial compressive strength (UCS), the test samples shall be right circular cylinders having a length to diameter ratio of 2.5e3.0 and a diameter preferentially of not less than NXsized core, roughly 54.7 mm. Further, before testing the UCS, UPV
test is generally measured on the same core specimens. Thus, the rock specimens having a non-standard length are ignored in tests based on the suggested methods. However, more reliable correlations may be obtained by adding the rock specimens having an threshold specimen length even if the non-standard lengths are used for only UPV testing. In relevant literature published around the world, no study has been carried out to investigate the effect of the core sample length on the UPV in intact rocks. In this study, it is hence aimed to investigate the effect of core sample length on the UPV in volcanic rocks and limestones, exploring the threshold specimen length. 2. Material and method 2.1. Sampling Eight rock types were sampled and rock blocks were collected from different locations in Trabzon, Giresun, Gumushane, Amasya, and Mugla regions of Turkey (Fig. 1, Table 1), four of which are volcanic rocks and four are limestones. Block samples used in this study were controlled for macroscopic imperfections such as cracks and weathering in order to that it might provide standard testing samples. As the anisotropic characteristics of rocks directly affect the ultrasonic P-wave velocity (Piniska, 1977) in this study, the rock types with free of anisotropy which are considered to be homogenous were preferred. No anisotropic rocks having schistosity, foliation and bedding plane were chosen to evaluate. Volcanic rock and limestone specimens were collected from the lithologically massive formations. Another significant factor that influences the UPV is the grain
Table 1 The location and lithology of rocks sampled. Rock code
Rock class
Rock Type
Lithology
Location
1 2 3 4 5 6 7 8
Igneous Igneous Igneous Igneous Sedimentary Sedimentary Sedimentary Sedimentary
Volcanic Volcanic Volcanic Volcanic Chemical Chemical Chemical Chemical
Andesite Basalt Vesicular basalt Dacite Beige limestone White limestone Black limestone Grey limestone
Trabzon/Arakli Giresun/Gorele Trabzon/Center Giresun/Tirebolu Amasya/Gumushacikoy Mugla/Yatagan Duzce/Akcakoca Gumushane/Torul
1.70 1.98 9.76 0.75 0.29 0.15 0.20 0.50
150 mm 125 mm 100 mm
1.45 1.85 9.75 0.82 0.31 0.25 0.22 0.52 1.48 1.72 9.70 0.95 0.27 0.20 0.20 0.52
75 mm 50 mm
1.83 2.22 9.40 1.62 0.26 0.24 0.26 0.58 4750 4495 2798 5035 4632 5179 5147 3475
150 mm 125 mm
4733 4317 3294 5163 4579 5348 5200 4310 4772 4591 3603 5629 4643 4989 5399 4002
100 mm 75 mm
4701 4590 3959 5515 3874 3739 4589 3137
50 mm
3853 3282 3237 5224 3312 3439 4272 2227 4036 3842 3332 4386 3228 4283 4684 2852
150 mm 125 mm 100 mm
Andesite Basalt Vesicular basalt Dacite Beige limestone White limestone Black limestone Grey limestone 1 2 3 4 5 6 7 8
75 mm
4024 3734 3372 4308 3288 4381 4693 2798
50 mm
3796 3670 3390 4549 3292 4134 4544 2583
Average napp (%) Average UPVsat (m/s) Average UPVdry (m/s) Test number Lithology Rock code
Table 2 The average UPVdry, UPVsat, and napp values of rock samples.
The NX-sized core specimens used in the experimental studies were obtained from blocks to the required dimension using core drilling machine. The ends of the samples were machined for flat ground and made parallel to each other. The cut end faces of the core samples were smoothened to maintain precision of within ±0.02 mm and made perpendicular to within ±0.05 mm to the core axis using comparator. After a macroscopical checking, only unweathered, homogeneous, and free of visible joint specimens were considered. In order to obtain the exact results as well as the best comparison, the experiments were carried out under the same conditions. Core specimens were prepared at five different lengths with the same diameter for each rock type. The core length for the smallest specimen is 50 mm and 150 mm for the longest specimen. The core diameters are the same (NX: 54.7 mm) in order to minimize the interaction between the UPV and the core diameter. The UPV testing applied on the dry and saturated specimens. Ultrasonic pulse method for the UPV testing was performed using the Pundit-plus model equipment. An accuracy of 0.1 mm for the length of the measuring base was used. Before the measurements, the cut ends of samples were polished to provide flat and smooth surface. A thin film of petroleum jelly (vaseline) was fulfilled to the surface of the transducers (receiver and transmitter) so as to provide full contact and to remove the air gap between transducers and the specimen surface. In the laboratory, direct, semidirect and indirect methods could be performed for UPV measurement. The direct procedure known to be the most reliable and satisfactory method, was performed during the test in order that the receiver and transmitter might be positioned on the opposite cut end surfaces of the samples used. In the tests, the ultrasonic pulse time was measured with an accuracy of 0.1 ms. The UPV was obtained by dividing the length of the NX-sized core and the travel pulse time. Mean UPV value was obtained by averaging the P-wave values of five tests on the same lithology type. A total of 200 core specimens having different lengths were used in the experiments. Core specimens used for UPV measurement were also evaluated in the calculation of apparent porosity. The sample volume was determined from an average of three caliper readings. Samples were saturated with distilled water at room temperature for 24 h. Achieving 100% saturation is theoretically impossible for homogeneous rocks apart from the clastic rocks due to unconnected voids in their structures. However, the assumption of 100% saturation is made after 24/48 h in distilled water for homogeneous volcanic, plutonic rocks and limestones which have apparent porosity (e.g. Sharma and Singh, 2008; Fener, 2011; Karaman and Kesimal, 2015; Kaya and Karaman, 2015; Karaman et al., 2015). After the saturated core specimens were performed for UPV tests, weight of each specimen was calculated. The dry weight of samples was defined after drying for 24 h at a temperature of 105 C in oven. The values of apparent porosity were obtained using saturation and caliper techniques. The volume of pores was determined from dry and saturated weights. Apparent porosity values of each sample were derived from the ratio of the void volumes to the sample volume. All tests were implemented based
3705 3682 3174 4377 2870 2983 4042 2237
2.2. Experimental procedures
3235 2502 2469 4029 2417 2195 3850 1700
size of the minerals. The travel length of the pulse though the rock samples shall be at least 10 times the mean grain size based on the ISRM (2014) suggested methods. For this reason, volcanic (extrusive) rocks with aphanitic textures (micro minerals are distributed in matrix) and limestones with micritic matrixs were used for experimental studies to provide required sample lengths.
1.47 1.72 10.60 0.97 0.30 0.18 0.30 0.55
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25 25 25 25 25 25 25 25
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on the ISRM (2007) suggested methods, and results of all experimental studies were given in Table 2. 2.3. Evaluation of the test results Evaluation of the data obtained from laboratory studies were performed in two stages. In first stage, the relationships between ultrasonic P-wave velocities under dry and saturated conditions (UPVdry and UPVsat) and apparent porosity (napp %) were investigated using regression analyses for each length. Therefore, the regression lines/curves were drawn for the UPVdry-UPVsat and UPVdry-napp data pairs belong to volcanic rocks and limestones studied. Since porosity is directly affecting the UPV, this parameter is used in the regression analyses. In second stage, the threshold specimen lengths of the NX-sized volcanic rocks and limestones were determined according to the UPV values. The detailed information about this method was given in later stages. 3. Results and discussion 3.1. Results The regression analyses were performed for each specimen
145
length varies between 50 and 150 mm. As shown in Fig. 2, the UPV values obtained from dry and saturated specimens are well correlated and two different trends were observed for volcanic rocks and limestones. The equations of the best-fit lines and the correlation coefficients (r) were determined for each regression. Strong relationships (r: 0.81e0.99) were obtained for the UPVdry and UPVsat. Kahraman (2007) correlated the UPVdry and UPVsat. for all rocks, igneous, metamorphic and sedimentary rocks with different porosity values (lower and higher than 1%). The UPVdry was also correlated with the apparent porosity (napp %). The rocks were classified into two groups based on their geological origins such as volcanic and chemical sedimentary (limestones). The vesicular basalt exhibits a different distribution unlike other volcanic rocks due to its high porosity values (Fig. 3). Therefore, lower UPV for the vesicular basalt was obtained compared to other rocks studied. Since number of rocks having high porosity values is insufficient in this study, the correlation coefficient (r) will not reliable for vesicular basalt. Thus, it was not taken into account in the regression analyses. Significant relationships were found among the parameters, and two different trends were seen for the volcanic rocks and limestones. There is a big difference between the two trends. Limestones follow a more steeply trend line than that of volcanic rocks. The different trend is likely to be related to the apparent porosity of limestones rocks that limited to a narrower range.
Fig. 2. UPVdry of the volcanic rocks and limestones in correlation with UPVsat.
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Sound velocity of dry rock specimens decreased with the increase of porosity. The average UPVdry and UPVsat values against specimen length were plotted for each rock lithology (Figs. 4 and 5). As shown in the figures, the UPVdry and UPVsat were remained constant or decreased (or at least fluctuate closely around a constant mean value) for NX-sized cores over the threshold length. In order to predict the threshold specimen length for a consistent UPV value, a method was developed. This method was carried out in two steps. Firstly, UPVdry-Sample length and UPVsat-Sample length data pairs belong to the volcanic rocks and limestones were correlated using regression analyses. Secondly, two regression lines were fitted to the data set; one is an inclined line fitted to the UPVdry and UPVsat values increasing with specimen length; the other is a nearly horizontal line fitted to UPVdry data and negative inclined line fitted to the UPVsat data, showing no or little changes with specimen length. It was considered that the value at the intersection point of two regression lines for each lithology is threshold specimen length value (Figs. 4 and 5). In Table 3, threshold specimen lengths are nearly same for both dry and saturated conditions. Therefore, threshold lengths of core specimens for the some volcanic rocks and limestones were determined by averaging their related values. The average threshold specimen lengths were given
in Table 3. From the table, the threshold specimen lengths were obtained as 79 and 109 mm for volcanic rocks and limestones, respectively. Based on the results of this study, the UPVdry and UPVsat values were approximately remained constant or decreased for cores having a length over the 75 mm for the volcanic rocks and 100 mm for the limestones. In the saturated UPV values, it was obtained higher decrease than the dry UPV values over the threshold specimen lengths usually in vesicular basalt and grey limestone specimens. 3.2. Discussion In the literature, there is a great deal of research exploring the effect of specimen size on the UCS (e.g. Thuro et al., 2001; ASTM, 2002; ISRM, 2007; Tuncay and Hasancebi, 2009; Darlington et al., 2011) and on Schmidt rebound hardness of rocks (e.g. ASTM, 2005b; ISRM, 2007; Demirdag et al., 2009). As for the UPV, ASTM (2005a) published a graph showing values of specimen diameter (in.), specimen length (in.) and average grain size versus the ratio of compression propagation velocity to resonance frequency. Whereas, the lateral minimum dimension is suggested to be not less than 10 times the wave-length based on the ISRM (2014). In addition to this, the travel distance of the pulse through the rock
Fig. 3. UPVdry of the volcanic rocks and limestones in correlation with napp.
K. Karaman et al. / Journal of African Earth Sciences 112 (2015) 142e149
sample shall be at least 10 times the mean grain size. However, it was commonly known that the length to diameter ratios varying from 2 to 3 were generally used by appliers in practice for UPV testing without determining the average grain size of the specimen. Therefore, this study could have made a significant contribution to practical solution of the UPV experiments especially for the some volcanic rocks and limestones. However, the length effect on intrusive rocks (granite, diorite, etc.) may be different from that on volcanic rocks and limestones; this should be further examined. 4. Conclusion In this study, NX-sized cores having lengths between 50 and
147
150 mm were evaluated to investigate the specimen length on the UPV. According to the findings derived from the present study, the main results were presented below; 1) The UPVdry-UPVsat and UPVdry-napp data pairs were correlated using regression analyses. Significant relationships were found among the parameters for the volcanic rocks and limestones. Two different trends were observed for those rock groups according to the regression analyses. Limestones followed a more steeply sloped line than that of volcanic rocks. 2) UPV values versus specimen length were plotted for all rocks. Core specimens having lengths 50 mm and 75 mm, an increase in the UPV values based on an increase in length was shown for
Fig. 4. Method for threshold specimen length determination for volcanic rocks and limestones using average UPVdry values.
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K. Karaman et al. / Journal of African Earth Sciences 112 (2015) 142e149
Fig. 5. Method for threshold specimen length determination for volcanic rocks and limestones using average UPVsat values.
the volcanics. Further, a significant increase in the UPV was obtained for limestone specimens having lengths 50 mm, 75 mm and 100 mm. Over the length of 75 mm for the volcanic rocks and 100 mm for the limestones, higher decreasing on UPV values was seen. This study showed that both the UPVdry and UPVsat are strongly contingent upon the variation of the specimen length. 3) According to the results of the statistical analyses, threshold specimen length for the volcanic rocks and limestones were determined as 79 and 109 mm, respectively. UPVdry values were remained constant or at least fluctuate closely around a constant mean value for NX-sized cores over the threshold
specimen length. However, UPVsat values were tended to decrease over the critical core specimen length for some rocks (vesicular basalt and grey limestone). These results rendered the UPV measurements unnecessary for the core samples over the length of 79 and 109 mm for the volcanic rocks and limestones, respectively. 4) Threshold specimen length was tried to predict for some rocks studied (i.e. volcanics and limestones). However, this only goes for the eight types of rock used and additional research on different rock types are needed especially for intrusive and metamorphic rocks as well as anisotropic rocks.
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Table 3 The threshold specimen length for volcanic rocks and limestones according to average UPVdry and UPVsat values. Rock code
Lithology
1 2 3 4
Andesite Basalt Vesicular basalt Dacite
5 6 7 8
Beige limestone White limestone Black limestone Grey limestone
a b
Threshold specimen length for each rock lithology (mm) According to average UPVdry
According to average UPVsat
76 73 83 85 79a 104 109 115 104 108b
76 75 76 87 79a 104 119 98 117 110b
Threshold specimen length for volcanic rocks. Threshold specimen length for limestones.
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