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(2) Exploration Geophysics. J. T. Kim et al.. Hammer. Hammer. js. Geophones. S-R1=8m S-R1=2m. R1-R2=8m Hammer. Geophones. S-R1=6m. R1-R2=2m. SASW Method. js. DR= 1m or 2m. Hammer. MASW Method. js. R1-R2=2m. S-R1=6m. HWAW Method. Fig. 2. Schematic diagram of surface wave methods (Bang, 2006).. Distance (m) 0. 20. 40. 60. 80. 100. 120. 140. 160. 180. 200. 220. 240. 260. 280. 0 –20 –40 –60 1. 50. 100. 150. 300. 600. 1200 2400. Resistivity (Ω-m) Fig. 3. 2D image of DC Resistivity results, showing a weak anomaly area in the core zone.. (a). Rock Fill zone. Surface wave method on the slope Core zone. Bedrock (b). Downstream side of dam. Core zone. Surface wave method on the crest X㡊ῂṚOXYU\tP. XW. {V wO㌗⮮䁷G ZG P. OuvUXZRX]U_PGGka_UZ. jvylG{ylujoGspul. OuvUXYR\U_PGGkaY_UW. Bedrock. OuvUXXRXXU_PGGkaY`U[. ]X. SPTUphole. Y_. Core zone. OuvUYRYUWPGGkaY\U[. OuvUXR`U\PGGkaX_U\. Dapth (m). 10. Fig. 4. Shape and locations of in-situ surveys in the core and rock-fill zone of the ‘M’ dam. (a) Cross-section and locations of in-situ surveys in the rock-fill zone. (b) Vertical section and locations of the in-situ survey in the core zone..
(3) Applicability of the surface wave method to rock fill dams. It has been well known that soil behaves non-linearly for small strains. The maximum shear modulus (Gmax) below the elastic threshold strain, g te, which is a fundamental stiffness parameter in design, is usually inferred from the Vs profile obtained by seismic wave propagation tests. The variation in shear modulus with strain can be determined at small to intermediate strains by resonant column, torsional shear, and triaxial testing equipment and the normalised modulus reduction curve (G/Gmax versus log g) can be found for each layer. Because the modulus value obtained by laboratory testing is affected by sampling disturbance and is difficult to regard as representative of a site, reliable non-linear stiffness variation is usually determined by combining Gmax obtained by field seismic tests and G/Gmax curves from laboratory tests. Gmax converted from the Vs profile can be used as the key soil property for deformation analysis of soil-foundation systems. In current design practice, the Vs profile of the core and rockfill zone of a dam is seldom determined by seismic methods because the borehole seismic method is often restricted in application, due to stabilisation activities and concern for the security of the dam structure, and surface wave methods are limited by unfavourable in-situ site conditions. Consequently, seismic response design for rock-fill dams is performed using an assumed Vs value or an empirical equation recommended by Sawada and Takahashi (1975). For reliable deformation analysis of rock-fill dams, therefore, it is necessary to obtain representative Vs profiles by in-situ seismic tests, by overcoming current difficulties.. Exploration Geophysics. 11. A further difficulty is that the surface wave method has a fundamental assumption that the evaluated system consists of a set of homogeneous layers of constant thickness. In reality, (a) 0.02 sec. slope 0.75. (b) 0.02 sec. (a) Sour ce. R1. R2. R1. R2. θ. YWWGV. slope 0.75. [WWGV [WWGV. (b). Vel. of Rayleigh wave (m/s). Fig. 6. Propagation shape at the sloping surface. (a) Vertical source. (b) Normal source.. 500. (a). Upslope0.5 Downslope0.5 TH2D_slope0.5. 400 300 200 100 0. 0. 20. 40. 60. 80. 100. Vel. of Rayleigh wave (m/s). Frequency (Hz) 500. (b). Upslope0.5_NS. 400. Downslope0.5_NS. 300. TH2D_slope0.5. 200 100 0. 0. 20. 40. 60. 80. 100. Frequency (Hz). Fig. 5. Schematic diagram and axis-symmetric modelling of ground model. (a) Schematic diagram of ground model. (b) Axis-symmetric modelling of sloped surface.. Fig. 7. Comparison of dispersion curves for vertical and normal source in numerical analysis. (a) Dispersion curves for vertical source. (b) Dispersion curves for normal source..
(4) 12. Exploration Geophysics. J. T. Kim et al.. however, such ideal conditions cannot be obtained. Specifically, dams have such geometric characteristics as horizontal variation of component materials (core and rock-fill zone) and finite boundaries with sloping surfaces. Surface wave observations influenced by reflection and interference of waves from different boundaries could result in distortion of the dispersion curve and subsequent results that include fatal errors. Therefore, it is very important to understand the reliability and (a) Receiver array. applicability of the surface wave method when it is used in the investigation of a dam, and a numerical study is needed to assess these problems. In this study, Vs profiles in the core and rock-fill zones were determined by Standard Penetration Testing-Uphole (SPT-Uphole; Bang and Kim, 2007), Spectral Analysis of Surface Waves (SASW; Nazarian and Stokoe, 1984), and Harmonic Wavelet Analysis of Wave (HWAW; Park and Kim, (d) Core: 200 m/s Core: 400 m/s. Source. Rock fill zone. Core: 600 m/s. Core zone Bed rock: 1000 m/s. Bed rock. (e). (b). Core: 400 m/s. Core: 200 m/s Core: 400 m/s. Core: 600 m/s. Rock fill: 300 m/s. Rock fill: 600 m/s Rock fill: 900 m/s. Bed rock: 1000 m/s. Bed rock: 1000 m/s. (c) Core: 400 m/s. Rock fill: 600 m/s. Bed rock: 1000 m/s. Fig. 8. Numerical modelling of ‘M’ dam. (a) 3D numerical model of ‘M’ dam (downstream section). (b) 400 m/s model with core zone only for comparative study. (c) 400 m/s model with core and rock-fill zones. (d) Layered model with core zone only for comparative study. (e) Layered model with core and rock-fill zones..
(5) Applicability of the surface wave method to rock fill dams. To obtain a shear-wave velocity profile, seismic borehole methods such as the Crosshole test, Downhole test, or SPTUphole method, or seismic surface wave methods such as SASW, Multi-channel Analysis of Surface Waves (MASW), and the new, innovative HWAW methods have been used in the field. Surface wave methods have great potential for rapid and economical determination of the Vs profile of the ground without boring. For dam safety reasons, it is difficult to perform boring, and reliable surface wave methods are urgently needed. In this study, boring with SPT was performed on the dam crest, and borehole seismic studies, especially SPT-Uphole observations, were carried out to measure the N-value and a Vs profile of the core zone, which can be used as a reference value. This is a form of the SPT-Uphole method, modified to obtain the Vs profile of a site effectively, and a schematic diagram of the method is shown in Figure 1 suggested by Bang and Kim (2007). This method uses SPT as a source to generate the impact energy for the seismic testing and performs the test during SPT. Boring and SPT-Uphole test are performed in tandem; therefore, the SPT-Uphole method can be performed simultaneously while boring, without the additional cost required for the preparation of the test hole (including the casing, grouting, and sourcing work) compared to other borehole seismic methods. For this reason, it is usually very simple, economical and not labour intensive. To apply the surface wave method on the crest of the dam and on sloping ground, the SASW and HWAW methods as shown in Figure 2 were chosen for this study because of the efficiency of testing and cost effectiveness. The SASW test uses the spectral analysis of surface waves generated by an impulsive source and recorded by a pair of receivers; the system then produces a dispersion curve by calculating the phase difference between each deployment of receiver pairs (Nazarian and Stokoe, 1984). Compared to SASW, the HWAW method, based on the harmonic wavelet transform, uses relatively short receiver spacings and is quick to set up; it has great advantages for 2D Vs imaging (Park and Kim, 2001). The HWAW method mainly uses the surface wave signal where the signal/noise ratio is maximum to evaluate the phase velocity and so can reduce the effects of noise. The surface wave method has a fundamental assumption, that the evaluated system consists of a set of homogeneous layers of constant thickness (Nazarian and Stokoe, 1984); but, in reality, such ideal conditions cannot be obtained. For example, the thickness of each layer varies with location, and most sites contain inclined layers. Also, dams have typical geometric characteristics such as horizontal variation of materials (core and rock-fill zone), and finite boundaries with sloping surfaces. Borehole methods using first-arrival time of waves are little influenced by reflection and interference of waves at interfaces with surrounding materials and boundaries of the site. In contrast to the borehole method, surface wave methods using full waveform analysis are influenced by reflection and interference of waves at different boundaries, and some. Outline of geophysical surveys of the existing ‘M’ dam In this study, to assess reliable methods for obtaining reasonable shear wave velocities in core and rock-fill zone, SPT-Uphole, SASW, and HWAW methods were performed on the crest and sloping surface of the existing ‘M’ dam in Korea. The ‘M’ dam is 60.7 m in height, 287 m in length; the crest elevation is 853.5 m and the crest width is 10 m. Before the boring and seismic survey, DC resistivity tests were carried out along the dam crest and found a low resistivity anomaly in part of the core zone, which was interpreted to be a weak zone (Figure 3). Therefore, boring with standard penetration tests (SPT) was carried out, and SPT-Uphole tests Vertical behaviour 1.5E-08. (a). 1.0E-08. Lamb_vel r=6 ABAQUS_vel r=6. Velocity (m/s). Seismic methods to evaluate the Vs profile in a rock-fill dam. 13. distortion in the dispersion curve of the surface wave method can appear so that results can include fatal errors. In addition, because each surface wave method has its own characteristics in testing and data analysis, the Vs profiles obtained from each test may not coincide. Therefore, it is very important to recognise the reliability and applicability of surface wave methods chosen for investigation of dams, and numerical studies are needed to assess these problems. Several researchers have already studied the effects of inclined layers (Gucunski et al., 1996; Yoon, 2000; Ludovic et al., 2004). The effects of a sloping ground surface, and of variation in surrounding materials, on the Vs profile, however, have not been studied.. 5.0E-09. 0.0E+00 0.00. 0.02. 0.04. 0.06. 0.08. 0.10. 0.12. –5.0E-09. –1.0E-08. –1.5E-08. Time (s) Vertical behaviour 8.0E-09. (b) 6.0E-09 Lamb_vel r=8 4.0E-09. Velocity (m/s). 2001) methods on the crest and sloping surface of the existing ‘M’ dam. To verify the applicability of the surface wave methods for rock-fill dams, and to find a reliable method for measuring the Vs profile, numerical analysis was performed, and the resulting Vs profiles were compared with the widely used empirical method.. Exploration Geophysics. ABAQUS_vel r=8. 2.0E-09 0.0E+00 0.00 –2.0E-09. 0.02. 0.04. 0.06. 0.08. 0.10. 0.12. –4.0E-09 –6.0E-09 –8.0E-09 –1.0E-08. Time (s) Fig. 9. Vertical particle velocity behaviour from 3D modelling. (a) Vertical particle velocity on 400 m/s model (r = 6 m). (b) Vertical particle velocity on 400 m/s model (r = 8 m)..
(6) 14. Exploration Geophysics. J. T. Kim et al.. were performed at that area. Then, the surface wave methods SASW and HWAW were performed, with the survey line passing through the borehole location to evaluate the Vs profile of the core zone. On the sloping surface of the downstream side of. dam, SASW and HWAW methods were performed to measure the Vs profile of rock-fill zone. Figure 4 shows the locations of the in-situ seismic surveys in the core and rock-fill zone of the ‘M’ dam.. (a). (b) 2 m° 4 m° 6 m° 8 m° 10 m° 12 m° 14 m° 16 m° 18 m° 20 m° 22 m° 24 m° 26 m° 28 m° 30 m° 32 m° 34 m° 36 m° 38 m° 40 m° 42 m° 44 m° 46 m° 48 m° 50 m° 52 m° 54 m° 56 m° 58 m° 60 m° 62 m° 64 m° 0. 0.2. 0.4. 0.6. 0.8. 1.0. Time (s) Fig. 10. Wave propagation and the acquired signals in numerical modelling of the ‘M’ dam. (a) Shape of wave propagation along core zone in rock-fill dam. (b) The signals acquired at receiver locations..
(7) Applicability of the surface wave method to rock fill dams. Exploration Geophysics. Numerical analysis. Vs (m/s). To verify the applicability of the surface wave method to rock-fill dams, two types of numerical analysis were performed. One simulated the surface wave method on a sloping ground surface to check its applicability to the sloping surface of the rock-fill zone. The other simulated the surface wave method on a material with a finite boundary with surrounding materials, for application to the evaluation of core stiffness by testing on the crest of dam.. 0. 100. 200. 300. 400. 500. 600. 5 10. Depth (m). 15. Numerical analysis was performed, varying several parameters such as slope angle, direction of wave propagation, setup of source, and stiffness contrast on a sloping ground surface (Kim et al., 2009). The numerical model consisted of two layers (Figure 5) and had a width of 80 m. The upper layer had a thickness of 3 m and the lower one had a thickness of 37 m. The infinite elements were half the size of the finite elements (FE) in the model. A four-node bilinear axis-symmetric quadrilateral element (CAX4) with infinite elements (CINAX4) as the absorbing boundary was implemented, and the size was 0.1 m in the upper layer and 0.2 m in the lower one. This study utilises 10 elements to express a single wavelength (Ihlenburg, 1998). The calculation time step was 0.5 ms. Numerical processing was performed up to 8 s (ABAQUS/Standard Version 6.5). An impact force of 1N was applied as a source. First, a vertical source (in the gravity direction) was applied. After 0.02 s had elapsed, the wave propagation shape was shown in Figure 6a. The shapes of the propagating wave in the upslope and downslope directions were different and the shape was. Phase velocity (m/s). 0. (a). Simulation of surface wave method on sloping ground. 20 25 Vs: reference Vs by core+rock fill model. 30 35 40 45. Vs (m/s) 0. 200. 400. 600. 800. 0. (b) 5. Depth (m). 10. 15. 20. Dispersion curve. 25. 550. Theoretical dispersion curve Kausel. 30. 500. Numerical analysis : only core. 600. 15. (a) Vs by core+rock fill model. Numerical analysis : core+rockfill. 450. Vs: reference. 35. 400. Fig. 12. Vs profiles interpreted from the numerical simulation dispersion curves. (a) Vs profiles for the 400 m/s numerical model. (b) Vs profiles for the layered numerical model.. 350 300 250. 400. 200 1. 10. 100. 350. Wavelength (m) Dispersion curve. (b). 550. Theoretical dispersion curve Kausel. 500. Numerical analysis : only core. 450. Numerical analysis : core+rockfill. 300. 250. Vs (m/s). Phase velocity (m/s). 600. 400 350. 200 Osaki and Iwasaki (1973) Osaki and Iwasaki (1973). 150. 300 250. Osaki and Iwasaki (1973) Imai and Tonouchi (1982) Imai and Tonouchi (1982) Zen et al. (1987) Average. 100. 200 150 100. 50. 1. 10. 100. Wavelength (m). 0 15. Fig. 11. Dispersion curves obtained by numerical analysis and analytic solution. (a) Dispersion curves for the 400 m/s model. (b) Dispersion curves for the layered model.. 25. 35. 45. N value from SPT (blows counts) Fig. 13. Vs profiles predicted by several empirical equations..
(8) 16. Exploration Geophysics. J. T. Kim et al.. asymmetric. So, experimental dispersion curves for upslope and downslope directions are not the same in the low frequency range, as is shown in Figure 7a, because reflected body waves distorted the phase information in normal signals recorded by the receivers. Otherwise, when a normal source was applied, the wave propagation shape was as shown in Figure 6b. The propagation shape upslope and downslope was symmetric about the axis of the normal source, and dispersion curves of both upslope and downslope were identical over the whole frequency range. This means that a signal reliable Vs profile could be found in this way. Whatever the source direction, wave fronts of surface waves are normal to the surface. Therefore, particle motion normal to the slope must be measured at the receivers. In conclusion, to apply the surface wave method to a sloping ground surface, the source impulse must be applied normal to the slope, and the receivers have to record normal. signals. Consequently, a unique Vs profile of the material forming the slope could be derived. Simulation of surface wave method on the crest of a dam When a surface wave method is applied on the crest of a dam to measure the Vs profile of the core zone, the core has a sloping boundary with the surrounding material, as shown in Figure 4a. Therefore, the effects of such conditions on the surface wave method have to be considered to evaluate a reliable Vs value. A 3D numerical model was constructed using geometric information about the downstream section of the ‘M’ dam (Figure 8a). A sixnode linear triangular prism (C3D6), wedge type, was implemented for the FE mesh of the slope section. Time increments for the numerical integration must always be smaller than the half period of the elastic wave. In the same. (a) 6m 9m 12 m 15 m 18 m 21 m 24 m 27 m. Receiver location. 33 m 36 m 39 m 42 m 45 m 48 m 51 m 54 m 57 m 60 m 63 m 66 m 69 m 72 m 0. 0.2. Time (s). 0.4. Fig. 14. Signal traces at each receiver location, for a source at a depth of 24.5 m. The mark is the first peak of the shear wave component. (a) Vertical component. (b) Horizontal component. (c) Sum of two components..
(9) Applicability of the surface wave method to rock fill dams. Exploration Geophysics. manner, the spatial resolution requires that the size of the elements be shorter than half of its wavelength. This study utilises 10 elements to express a single wavelength (Ihlenburg, 1998). Thus, it is possible to determine the element size (le) according to the shortest wavelength (lmin) of interest, and the time integration (ti) with the highest frequency (fmax) in the same manner. This study adopts a 0.5 ms integrating time step and 0.2 m minimum element size, in order to simulate surface waves with a maximum frequency of 200 Hz and a minimum wavelength of 2 m. In deep layers, longer wavelengths are of interest, and waves propagate through the ground at depths similar to their wavelength. Therefore, for efficient FEM analysis, element size increases with depth to a maximum of 1 m. The source, which is a 4th order force-time function of 1N with a contact time tc = 40 ms, was applied at the top end of the model, representing the crest of the dam. Along the crest of the dam 32 receivers were located to acquire signals. Numerical (b). processing was performed up to 8 s (ABAQUS/Standard Version 6.5). In this study, comparative analysis was performed with two types of input parameters. One is a model of uniform lateral composition, with values typical of the core zone (Figure 8b, d ). The other is a model which includes stiffness contrast between core and rock-fill material, simulating real dam (Figure 8c, e). The shear wave velocities defined in the core-only model were 400 m/s in the uniform model, and 200, 400, 600 m/s in the layered model. The shear wave velocities in the rock-fill material in the core + rock-fill model were set at 600 m/s in the uniform model, and 300, 600, 900 m/s in the layered model. The shear velocities in the rock-fill zone were assumed to be 1.5 times those of the core zone, to represent the stiffness contrast between core and rock-fill material. To apply this 3D numerical modelling to simulation of a surface wave method, verification of the representation of the. 6m 9m 12 m 15 m 18 m 21 m 24 m 27 m. Receiver location. 33 m 36 m 39 m 42 m 45 m 48 m 51 m 54 m 57 m 60 m 63 m 66 m 69 m 72 m 0. 17. 0.4. 0.2. Time (s) Fig. 14. (Continued).
(10) 18. Exploration Geophysics. J. T. Kim et al.. full waveform, including P wave, S wave, and Rayleigh wave, is required. A theoretical solution to Lamb’s problem (Achenbach, 1975), for motions of a homogeneous isotropic half-space subjected to a concentrated normal load, was compared with the particle velocity of waves at two points obtained from the numerical core-only model with the same source (Figure 9). The vertical particle velocities obtained from the 3D numerical simulation match well with the theoretical solutions, and this means that the 3D modelling is suitable for simulation of surface waves. Figure 10 shows the shape of wave propagation along the core zone in the rock-fill dam and examples of signal traces at each modelled receiver. Using these signals, the experimental dispersion curves were determined. In Figure 11, dispersion curves obtained by numerical modelling are compared with the theoretical dispersion curve obtained by Kausel’s method for half-infinite ground model. In the case of a 400 m/s model, as. shown in Figure 11a, dispersion curves from the theoretical solution and the core-only model are similar over the whole range of wavelengths. This means that the dispersion curve is only slightly influenced by reflection and interference of waves caused by the finite boundary and sloping surface, because the width is relatively large when compared to the depth of the dam. However, for a model composed of core and rock-fill zones, the phase velocities are overestimated, and differ from the theoretical one over the whole range of wavelengths. Because of the narrow width of the core zone, wave propagation is influenced by reflection and interference of waves arising from the stiffness contrast between the core and rock-fill zones; consequently, some distortion in the dispersion curve appears and the result can include significant error. For the layered model, which represents real ground condition more closely than the uniform (400 m/s) model, the same trend is also seen in Figure 11b. But, the overestimation is much less than in the 400 m/s model case,. (c) 6m 9m 12 m 15 m 18 m 21 m 24 m 27 m. Receiver location. 33 m 36 m 39 m 42 m 45 m 48 m 51 m 54 m 57 m 60 m 63 m 66 m 69 m 72 m 0. 0.4. 0.2. Time (s) Fig. 14. (Continued).
(11) Applicability of the surface wave method to rock fill dams. Exploration Geophysics. Vs (m/s) 200 0. 400. 600. 800 6m 9m 12 m 15 m 18 m. 10. 21 m 24 m 27 m 36 m 39 m 42 m. 20. Depth (m). 45 m 48 m 51 m. 19. so that results of this model may include less error than uniform model. In Figure 12, Vs profiles obtained from the dispersion curves for the core and rock-fill models are compared with reference velocities for each model. The shear wave velocities obtained by numerical analysis are overestimated compared with the reference values. While the velocity calculated for the 400 m/s model is more than 500 m/s below 7 m of depth, the velocities obtained from the layered model are a little bigger than the input Vs values, and might be used in engineering analysis. Generally, soil strata are similar to the layered model, and the stiffness ratio (1.5 times) between core and rock-fill materials used in this study is thought to be the maximum value of that ratio. Consequently, it can be concluded that the surface wave method can be applied on the crest of the ‘M’ dam although resulting values might be a little overestimated.. 57 m 60 m. 30. 63 m. Results of in-situ tests. 66 m. Boring with SPT. 69 m 72 m Average Vs 40. 50. Fig. 15. Vs profile at each receiver location, from the SPT-Uphole survey. The bold line is the average value.. Boring was performed on the crest of the dam, to a depth of 50 m. The ground was uniformly core zone material, and SPT-N values were adjusted with reference to energy ratio N60. To evaluate the Vs profile of the core zone, several empirical equations were used, and results are shown in Figure 13 (Ohsaki and Iwasaki, 1973; Imai and Tonouchi, 1982; Zen et al., 1987). Shear wave velocities in the core zone determined from SPT N values varied from 200 m/s to 370 m/s; the averaged value is shown in Figure 13. Vs (m/s). Dispersion curve. 600. Phase velocity (m/s). 200 0. 400. 600. 800. 1000. (a). 500. 2m. 8m. 16 m. 24 m. 32 m. THD. 400 300 10. 200. M dam_HWAW 100. M dam_SASW. 0 1. 10. 100. Depth (m). Wave length (m) Dispersion curve Phase velocity (m/s). 600. (b). 500. THD. 20. EXD. 400 300 200. 30. 100 0 1. 10. 100. Wave length (m) Fig. 16. Experimental and theoretical dispersion curves from surface wave methods in the core zone. (a) Experimental and theoretical dispersion curves from the SASW method. (b) Experimental and theoretical dispersion curves from the HWAW method.. 40. Fig. 17. Vs profiles from surface wave methods in the core zone..
(12) 20. Exploration Geophysics. J. T. Kim et al.. SPT-Uphole method Measurements using the SPT-Uphole method were made during boring. Using two-component (radial-horizontal and vertical) geophones is recommended to obtain better travel time information from deep sources (Bang and Kim, 2007). Figure 14a and b show examples of measured signal traces of the vertical and horizontal components from each receiver location, for a source at 24.5 m depth. Twenty-two pairs of vertical and horizontal geophones were used, and the receivers were located from 6 m to 72 m from the borehole, at a spacing of 3 m. Figure 14c shows a plot the root mean square signals of the vertical and horizontal components in the time domain (the sum of two-component signals). The travel time of the shear wave was obtained by using the peak point of the sum of two-component signals. Figure 15 shows the Vs profiles at each receiver location, from travel time information obtained from sum of two-component signals from sources at all depths. As shown in Figure 15, Vs profiles are in a narrow range as a whole, except for some outlier points from errors in field testing. This means that the core zone of ‘M’ dam is horizontally uniform. Using those Vs profiles, average shear wave velocity as a function of depth was calculated and is plotted with a bold line in Figure 15. SASW and HWAW method in core zone SASW and HWAW surveys were performed on the crest of the dam near the borehole. The receiver spacing for the SASW method was increased from 2 m to 48 m, and the receiver spacing and source offset for the HWAW method, which uses a single array, were 10 m and 2 m. Figure 16 shows experimental and theoretical dispersion curves for each method; Figure 17 shows the resulting Vs profiles. The experimental dispersion. curve and theoretical dispersion curves are labelled with EXD and THD in the figure. The dispersion curves were calculated to ~90 m of wavelength; Vs profiles lay in the range of 200–620 m/s to a depth of 35 m. The Vs profiles from the SASW and HWAW methods are very similar. Since the trend of the Vs profiles resembles that of the input velocity function for the numerical layered model, the numerical analysis suggests that the results of the surface wave methods might be only slightly influenced by the stiffness contrast between core and rock-fill zone materials. So, it is thought that the surface wave methods have resulted in reasonable values for core properties, even though the resulting values could be a little overestimated. SASW and HWAW method in rock-fill zone If a dam has a berm in the rock-fill zone, it is easier to perform surface wave surveys. But not every dam has a berm, and therefore surface wave surveys must be performed on sloping surfaces as in this example. On a sloping surface, receivers are established normal to the surface and the source impact was normal to the surface, using a urethane sledge hammer. The SASW and HWAW surveys were performed in the downslope direction. The receiver spacing in the SASW method ranged from 2 m to 24 m, and receiver spacing and source offset for the HWAW method were 10 m and 2 m respectively. Figure 18 shows experimental and theoretical dispersion curves from each method; Figure 19 shows the resulting Vs profiles. Dispersion curves were calculated to ~30 m of wavelength, and the Vs values lay in the range of 150–400 m/s. When testing on a sloping surface, it is difficult to generate a source Vs (m/s) 0. Dispersion curve. 500. 0. 200. 400. 600. 800. Phase velocity (m/s). (a) M dam_SASW. 400. M dam_HWAW 300 200 100. 2m. 4m. 16 m. 16 m. 24 m. THD. 5. 0 1. 10. 100. Depth (m). Wave length (m) Dispersion curve. 500. Phase velocity (m/s). (b) 400 300. 10 200 THD. EXD. 100 0 1. 10. 100. Wave length (m) Fig. 18. Experimental and theoretical dispersion curves from surface wave methods in the rock-fill zone. (a) Experimental and theoretical dispersion curves from the SASW method. (b) Experimental and theoretical dispersion curves from the HWAW method.. 15. Fig. 19. Vs profiles from surface wave methods in the rock-fill zone..
(13) Applicability of the surface wave method to rock fill dams. Exploration Geophysics. with high energy and low frequency. Therefore the survey line and the resulting dispersion curve are relatively shorter. The Vs profiles from the SASW and HWAW methods are very similar. The ratios of Vs between core and rock-fill materials at the same depth are in the range of 1 to 1.2, which supports the conclusion that the Vs evaluated from surface wave surveys in the core zone of the ‘M’ dam are reasonable. Comparison of results of several tests with empirical equation calculations To evaluate the shear wave velocities for the rock-fill dam, the results obtained by field tests were compared with the empirical equation suggested by Sawada and Takahashi (1975). Figure 20 shows a comparison of observed and empirical Vs in the core zone. The results of the seismic methods match well with the lower limit of the empirical equation; however, Vs predicted from SPT-N observations is underestimated over the whole range of depths. Consequently, the seismic method, applied at the crest of a dam, is reasonable for evaluating Vs in the core zone. However, additional parametric studies should be required, using various models and input parameters, before seismic methods are applied to general rock-fill dams. Figure 21 shows a comparison of Vs results in the rock-fill zone. As shown in the figure, the results of surface wave surveys match well with the empirical equation, although Vs profiles at greater depths on the slope could not be obtained. This shows that the surface wave methods can deal successfully with unfavourable field conditions, such as a sloping surface and material composed of rubble stone, and still present a reliable. 21. value for rock-fill zone properties. So, after improving the test setup, including providing appropriate impact sources and receivers, surface wave methods can evaluate the Vs profile of the rock-fill zone for the whole range of depths. Conclusion In this study, to find a reliable method for estimating shear wave velocities in core and rock-fill materials in a rock fill dam, boring, and a range of seismic methods including SPTUphole, SASW, and HWAW methods, were performed on the crest and sloping surface of the existing ‘M’ dam. Also, numerical analysis was performed to verify the applicability of surface wave methods to a rock-fill dam. Finally, Vs profiles derived from each method were compared with results of the empirical method of Sawada and Takahashi (1975). From the results of the numerical simulation of surface wave methods on a sloping ground surface, it is concluded that the Vs profile of the material beneath the slope could be derived reasonably using a source and receiver aligned normal to the slope surface. Also, applying the surface wave method on the crest of a dam gives reasonable velocities in this example, but the simulation shows that results could include a little error possibly due to reflection of waves from the boundary between the core and rock-fill zone. Through field tests and comparison with empirical equation estimates, the seismic method is found to be reasonable for evaluation of Vs in the core zone. In general, because boring is restricted in dams, surface wave methods are recommended as reliable methods. However, additional parametric studies should generally be undertaken. For the rock-fill zone, the results of. Vs (m/s) 0. 400. 600. 800. 1000. Vs (m/s). 0. 0. 200. 400. 600. 800. 1000. 0 Sawada(1975) Core zone_ lower limit. 10. Sawada(1975) Rockfill zone_ unsaturated. Sawada(1975) Core zone_ upper limit Vs by SPT-N value HWAW. SASW. SASW. HWAW. SPT-Uphole. Depth (m). Depth (m). 20. 10. Sawada(1975) Rockfill zone_ saturated. 20. 30. 30 40. 40 50. Fig. 20. Comparison of Vs profiles from several methods in the core zone.. Fig. 21. Comparison of Vs profiles from several methods in the rock-fill zone..
(14) 22. Exploration Geophysics. surface wave methods match well with empirical equation estimates, and could be considered to be reliable. Surface wave methods deal successfully with unfavourable field conditions and, consequently, can evaluate the Vs profile of the rock-fill zone for the whole range of depths, if the test setup is chosen appropriately. Acknowledgments This study was supported by fund of Smart Infra Structure Technology Center (SISTeC) and field testing was supported by Korea Infrastructure Safety and Technology Corporation (KISTEC). All of them are gratefully acknowledged.. References ABAQUS/Standard Version 6.5 User Manual, Finite element software package: Hibbit, Karlsson & Sorenson, Inc. Achenbach, J. D., 1975, Wave propagation in elastic solids: Elsevier Science Ltd. Bang, E. S., 2006, Study on field seismic methods for obtaining reliable shear wave velocity profile, Dissertation, Doctor, KAIST. Bang, E. S., and Kim, D. S., 2007, Evaluation of shear wave velocity profile using SPT based uphole method: Soil Dynamics and Earthquake Engineering, 27, 741–758. doi:10.1016/j.soildyn.2006.12.004 Gucunski, N., Ganji, V., and Maher, M., 1996, Effect of soil nonhomogeneity on SASW testing: Proceedings of Uncertainty in Geologic Environment from Theory to Practice. Ihlenburg, F., 1998, Finite element analysis of acoustic scattering: Springer-Verlag.. J. T. Kim et al.. Imai, T., and Tonouchi, K., 1982, Correlation of N-value with S-wave velocity and shear modulus: Proceedings of the 2nd European Symposium of Penetration Testing, Amsterdam. Kim, J. T., Park, H. J., Kim, D. S., and Kim, S. W., 2009, Evaluation of the applicability of surface wave method on the sloping surface: Proceedings of 10th International Conference on Structural Safety and Reliability. Ludovic, B., Abraham, O., Bitri, A., Leparoux, D., and Côte, P., 2004, Effects of dipping layers on seismic surface waves profiling: a numerical study: Proceedings of Symposium on the Application of Geophysics to Engineering and Environmental Problems, Colorado Springs, CO. Nazarian, S., and Stokoe, K. H., 1984, In situ shear wave velocities from spectral analysis of surface wave: Proceedings of 8th Conference on Earthquake Engineering, San Francisco. Ohsaki, Y., and Iwasaki, R., 1973, On dynamic shear moduli and Poisson’s ratio of soil deposits: Soil and Foundation, 13, 61–73. Park, H. C., and Kim, D. S., 2001, Evaluation of the dispersive phase and group velocities using harmonic wavelet transform: NDT & E International, 34, 457–467. doi:10.1016/S0963-8695(00)00076-1 Sawada, Y., and Takahashi, T., 1975, Study on the material properties and the earthquake behaviors of rockfill dams: Proceedings of 4th Japan Earthquake Engineering Symposium, 695–702. Yoon, J. G., 2000, Application of the SASW method in an Inclined Layer – Numerical study, Dissertation, Master, KAIST. Zen, K., Yamazaki, H., and Umehara, Y., 1987, Experimental study on shear modulus and damping ratio of natural deposits for seismic response analysis: Report of the Port and Harbour Research Institute, 26, 41–113. Manuscript received 30 September 2009; accepted 3 December 2009..
(15) Applicability of the surface wave method to rock fill dams. Exploration Geophysics. 23. 斲崫堖櫖昢汞͑ 祢彺砒͑ 匶憛͑ 洇殯昷͑ 磏儆͑ 櫶割͑ ₖ㫛䌲1, ₖ☯㑮1, 䠢㭖1, 㦖㍳2, ₖ㎇㤆3 1 䞲ῃὒ䞯₆㑶㤦G Ị㍺G G 䢮ἓὋ䞯ὒG 2 䞲ῃ㰖㰞㧦㤦㡆ῂ㤦G 㰖㞞㩚㡆ῂG 3 䞲ῃ㻶☚Ὃ㌂G . 殚͑ 檃G ឪ⯲ ➆⅗√ ₩ ╆Ჿ√⯲ Ⲟគ㞦 ☧ᡞᜮ ᕎ⯫ត㨎▷ ❶ Ṿ⭊ ⶫ⬮㧶 ῖ○Ⰾᔲ, Ⱆ₲ⲛ⯖ᳶ 㪞ⰿ ❶㩲⯞ 㙏㨎 㬧㧲ᜮ ╆᳚ႚ Ṩ⹚ ⧤⧲. ❶㈮ᆏ 㕪╆ℯ⯲ ᅗ⭊ ឪ ㅎ⯲ ⧢ⲯ○ ₩ ⧢╛⯲ Ⰾ⮺ᳶ Ⲷ㧶ᢲᜮ ᅗ⭊ႚ Ṩᅺ, 㣶Ἆ㞦 ዊℯ⯚ ⪎⧟㧶 㪞ⰿⴊᄎ ᧦ῒ⩪ ⲛ⭃Ⰾ ⭃Ⰾ㧲⹚ ⧤⧲. ᰖ▶ ឪ⯲ ᕎ⯫ត㨎▷ ❶ 㪞ⰿ ❶㩲ᅊᆖ ⩠Ⰾ ῖ○⯞ ႚⲯ㧲⪆ ⲛ⭃㧲ᄊᔲ ῒ㩦 ⰪᵦḖ Ⰾ⭃㧲⪆ 㨎▷⯞ ⚲㨣㧲ᅺ Ⱒᜮ ❾ⲯⰎ. → ⪊ሆ⩪▶ᜮ ╆Ჿឪ⩪▶⯲ Ⲟគ㞦 ☧ᡞ⯲ 㬧 ₩ ❺ᵊ○ Ⱒᜮ Ⲟគ㞦 ☧ᡞ ㊻ⲯ ዊℯ⩪ រ㧶 ⪊ሆḖ ⚲㨣㧲ዊ ⮞㧲⪆ ❾ⴎ㧲ᜮ ‘M’ ឪ⯲ Ṣᶂ ₩ ╆Ἆ⩪▶ 㣶Ἆ㞦 ዊℯ⯞ ⚲㨣㧲⪚⯖Ἂ, 㣶Ἆ㞦 ዊℯ⯲ ⲛ⭃○⯞ ᄚ⸷㧲ዊ ⮞㧲⪆ ⚲㋲㨎▷⯞ ⚲㨣㧲⪚. ㇶⴟⲛ⯖ᳶ ឪㅎ ႛ √⯲ Ⲟគ㞦 ☧ᡞḖ ᡞ㈶㧲⪚⯖Ἂ, ⚲㋲㨎▷ᆖ 㕞○㞦 㕪╆ ₩ 㣶Ἆ㞦 ዊℯ⯲ ⋞ᇪ⪊ሆḖ 㙏㧲⪆ ╆Ჿឪ⩪▶⯲ 㣶Ἆ㞦 ዊℯ⯲ ⲛ⭃○⯞ ᄚ⸷㧲⪚. 渂殚檺䚲Ⳋ䕢G ₆⻫SG 㩚┾䕢G ㏣☚SG ㌂⩻╦SG 㕂⼓SG ㌂⩻G G. 㕙ᵄតᩏᴺߩࡠ࠶ࠢࡈࠖ࡞࠳ࡓ߳ߩㆡ↪ᕈ⹏ଔ ㊄ ㎠హ1㊄ ᧲ᵟ1ᧉ ᙗବ1ᣇ ㌁⏋2㊄ ⋭3 1 㖧࿖⑼ቇᛛⴚ㒮 2 㖧࿖⾰⾗Ḯ⎇ⓥ㒮 3 㖧࿖㋕␠ . ⷐ ᣦ㧦 ⴕߩ࠳ࡓ⸳⸘ߦ߅ߡޔ㔡േᔕ╵ߩ⸳⸘ߦ㑐ߒߡ㊀ⷐߥ․ᕈߩ߭ߣߟߢࠆ ߩ᧚ࠕࠦߣ᧚ࠢ࠶ࡠߩࡓ࠳ޔS ᵄㅦᐲ߇႐⹜㛎߆ࠄหቯߐࠇࠆߎߣߪ߹ࠇߢࠆޔߪࠇߎޕሹౝ㔡តᩏᴺ߇ࡓ࠳ޔო㕙ቯᎿߩᓇ㗀ߣ࠳ࡓߩ᭴ㅧߩ ోᕈ߳ߩ㈩ᘦߩߚߦߩߘޔㆡ↪߇㒢ቯߐࠇߡࠆ߆ࠄߢࠅߚ߹ޔ㕙ᵄតᩏߩታᣉߦߚߞߡ႐ߩ᧦ઙߩㆡਇㆡߦࠃ ߞߡߘߩㆡ↪߇㒢ቯߐࠇࠆ߆ࠄߢࠆߩࡓ࠳ޔߡߞࠃޕ㔡േᔕ╵ߩ⸳⸘ߦߪޔቯߐࠇߚ S ᵄㅦᐲߩ୯߿⚻ޔ㛎⊛ߦዉ߆ࠇ ߚ S ᵄㅦᐲߩ୯ࠍߞߡࠆߩ߇⁁ߢࠆߣ᧚ࠢ࠶ࡠߩࡓ࠳ޕਛᔃㇱߦ߅ߌࠆ S ᵄㅦᐲࠍផ▚ߒޔS ᵄㅦᐲࠍ⸘᷹ߔࠆା㗬 ᕈߩ㜞ᣇᴺࠍߺߟߌࠆߚߦޔታߔࠆ M ࠳ࡓߩ㗂ㇱߣᢳㇱಽߢ㕙ᵄតᩏᴺߩㆡ↪ࠍ⹜ߺߚߩߢࡓ࠳࡞ࠖࡈࠢ࠶ࡠޕ 㕙ᵄᴺߩㆡ↪ᕈࠍ⏕ߔࠆߚޔᢙ୯⸃ᨆ߽ⴕޔᢙ୯⸃ᨆߣ߶߆ߩ⹜㛎ߩ⚿ᨐߣߩᲧセ߆ࠄߩߢࡓ࠳࡞ࠖࡈࠢ࠶ࡠޔ 㕙ᵄតᩏᴺߩㆡ↪ᕈ߇⏕ߐࠇߚޕ ࠠࡢ࠼㧦ࡠ࠶ࠢࡈࠖ࡞࠳ࡓࡠ࠶ࠢࡈࠖ࡞ㇱ㕙ᵄតᩏᴺ5 ᵄㅦᐲᢿ㕙. http://www.publish.csiro.au/journals/eg.
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Hydrothermal exploration aboard the R/V Onnuri was performed along the northern Central Indian Ridge (CIR) between 8°S and 12°S in January 2010. The main objectives of this
