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105 APPENDIX B-3 Port Island Site â Site Characterization General Port Island is an artificial island in Osaka Bay near Kobe, Japan. Approximate locations of the Port Island and its downhole array (site) are shown in Figure B-1. Approximate site coordinates are 34.6718 degrees north latitude and 135.2054 east longitude. Figure B-1. Location of the Port Island Downhole Array with respect to the 1995 M 6.9 HyogokenâNanbu Earthquake Epicenter and the Port of Kobe Facilities. S i t e S i t e E p i c e n t e r o f t h e 1 9 9 5 M 6 . 9 H y o g o k e n â N a n b u E q . P o r t I s l a n d Do w n h o l e Ar r a y O s a k a Ba y K o b e P o r t I s l a n d K o b e Ai r p o r t 1 5 k m R o k k o
106 Geotechnical Instrumentation The Port Island site was instrumented with strong motion (SM) instruments. No pore water pressure transducers were installed. Layout of geotechnical instrumentation within idealized profile is shown in Figure B-2. Figure B-2. Interpreted Soil Profile and Geotechnical Instrumentation at the Port Island Site (modified after Iwasaki, 1995). The SM instruments A1 (ground surface) and A2 (16 m b.g.s.), embedded within the reclaimed layer, were used in evaluations documented in this study. HyogokenâNanbu Earthquake and Ground Motions The 1995 M 6.9 HyogokenâNanbu earthquake was a thrust event with an epicenter in the Osaka Bay, approximately 15 km from the site (Figure B-1). Relevant information is summarized in Table B-1. The earthquake induced relatively strong ground motion response of the site. Observed sand boils indicated that the reclaimed layer liquefied in the subject event (Bardet et al. 1995; Cubrinovski et al. 1996; Elgamal et al. 1996).
107 Table B-1. HygokenâNanbu Earthquake â Event and Strong Motion Parameters at the Site. Earthquake Date M R (km) PGA (N-S) ru Hyogoken- Nanbu January 17, 1995 6.9 15 Surface (A1) 16 m b.g.s. (downhole; A2) Within Reclaimed Land 0.348 g 0.576 g > 0.95 (Inferred) M = Moment Magnitude; R = Approximate site-to-source distance; PGA = Peak Ground Acceleration (larger of the two horizontal components); ru = Maximum recorded excess pore water pressure normalized by the vertical effective-stress; N-S = North-South (direction). Figure B-3 shows the acceleration histories recorded at Port Island in the 1995 M 6.9 Hygokenâ Nanbu earthquake in the North-South (N-S) direction. Both the free-field (i.e., ground surface) record and the record at 16 m b.g.s. are shown. The corresponding acceleration response spectra are shown in Figure B-4. (a) (b) Figure B-3. Acceleration Histories from the 1995 M 6.9 Hygoken-Nanbu Earthquake recorded at the Port Island site: (a) Ground Surface; (b) Recorded 16 m downhole.
108 Figure B-4. Surface and Downhole Spectra (N-S) in the 1995 M 6.9 HygokenâNanbu Earthquake. Geotechnical Information and Representative Soil Profile Construction of the Port Island started in 1966 and was completed in 1980. The island was created by means of deposition (i.e., dumping from barges) of cohesionless soil referred to as the "Mesa Soil" (mostly sand with cobbles and gravel). As reported by Akai et al. (1995), the Mesa Soil was mined from the Rokko Mountains, which are relatively close to the site. The soil was deposited a few meters above sea level, with a total thickness of reclaimed land of 18 m. Only the soil above the sea level was compacted. More information about the construction of Port Island can be found in Iwasaki (1995). The geotechnical investigation was performed before the 1995 M 6.9 HygogokenâNanbu earthquake, i.e., the results of investigation are representative of the pre-earthquake (i.e., pre- soil liquefaction) site conditions. The geotechnical investigation was performed at and in the immediate vicinity of the downhole array. Detailed information is presented in Iwasaki (1995), Nakakita and Watanabe (1977), and Cubrinovski et al. (1996). Site conditions within top 90 m were investigated. The investigations included soil sampling and classification, SPT sounding, and one in-borehole measurement of shear wave velocity. Processed, synthesized and interpreted results of past investigations are shown in Figure B-5.
109 (a) (b) Figure B-5. Results of Site Exploration Programs: (a) SPT sounding; (b) Relative Density. The SPT sounding blow counts (N) shown in Figure B-5 are as reported in Iwasaki (1985). They were converted to: (i) ðð 0 (energy-corrected SPT blow count), (ii) (ðð ) 0 (energy- and overburden-corrected SPT blow count), and (iii) (ðð ) 0ððð ð (equivalent clean sand energy- and overburden-corrected SPT blow count) using the Idriss and Boulanger (2010) procedure. The Cubrinovski and Ishihara (2001) correlation between SPT blow counts and relative density, ðð, of granular soils was used to calculated the ðð profile shown in Figure B-5. The representative shear wave velocity profile at the downhole array, as established by Iwasaki (1995), is shown in Figure B-6.
110 Figure B-6. Shear Wave Velocity Profile at Port Island Downhole Array (after Iwasaki, 1995). Material Properties Shear modulus reduction and damping curves for the "Mesa Soil" (mostly sand with cobbles and gravel) are not available. Based upon relative density of the âMesa Soilâ (45 â 60%; see Figure B-5(b)), modulus reduction curves for Monterey Sand (Dr = 45%) by Dobry et al. (1982), were selected. Monterey sand is coarse drainage sand that does not resemble the âMesa Soilâ in terms of grain size distribution. Dobry et al. (1982) did not present the damping curve curves for Monterey Sand (Dr = 45%). Therefore, damping curve was generated by constitutive modeling. In particular the MKZ model (Matasovic, 1993; Matasovic and Vucetic, 1993) was used to generate damping curve that accompanies the modulus reduction curve shown in Figure B-7. Figure B-7. Reclaimed Land at the Port Island Site; Modulus Reduction Curve for Monterey Sand (Dr = 45%) (after Dobry et al., 1982).
111 References Akai, K., Bray, J. D., Christian, J. T., Boulanger, R. W., and Al., E. (1995). Geotechnical Reconnaissance of the Effects of the January 17, 1995, Hyogoken-Nanbu Earthquake, Japan. U.S. Department of Commerce. Bardet, J. P., Oka, F., Sugito, M., and Yashima, A. (1995). The great Hanshin earthquake disaster, preliminary investigation report. University of Southern California, Los Angeles, California. Cubrinovski, M., and Ishihara, K. (2001). âCorrelation between penetration resistance and relative density of sandy soils.â 15th International Conference on Soil Mechanics and Geotechnical Engineering, University of Canterbury. Civil and Natural Resources Engineering., Istanbul, Turkey, 393â396. Cubrinovski, M., Ishihara, K., and Tanizawa, F. (1996). âNumerical simulation of the Kobe Port Island liquefaction.â Proc. 11th World Conf. Earthquake Engineering, Elsevier Science Ltd Acapulco, Mexico. Dobry, R., Ladd, R. S., Yokel, F. Y., Chung, R. M., and Powell, D. (1982). Prediction of pore water pressure buildup and liquefaction of sands during earthquakes by the cyclic strain method. National Bureau of Standards, U.S. Department of Commerce, U.S. Government Printing Office, Washington, D.C. Elgamal, A.-W., Zeghal, M., and Parra, E. (1996). âLiquefaction of reclaimed island in Kobe, Japan.â Journal of Geotechnical Engineering, American Society of Civil Engineers, 122(1), 39â49. Idriss, I. M., and Boulanger, R. W. (2010). SPT-based liquefaction triggering procedures. Report No. UCD/CGM-10/02, Davis, California. Iwasaki, Y. (1995). âGeological and geotechnical characteristics of Kobe area and strong ground motion records by 1995 Kobe earthquake Tsuchi-to-Kiso.â Japanese Soc. of Soil Mech. and Found. Engrg., 43(6), 15â20. Matasovic N. (1993), âSeismic Response of Composite Horizontally Layered Soil Deposits,â Ph.D. Dissertation, Civil Engineering Dept., University of California, Los Angeles, 483 p. Matasovic, N. and Vucetic, M. (1993), âCyclic Characterization of Liquefiable Sands,â ASCE Journal of Geotechnical Engineering, Vol. 119, No. 11, pp. 1805 1822. Nakakita, Y., and Watanabe, Y. (1977). âSoil stabilization by preloading in Kobe Port Island.â Proc. 9th Int. Conf. on Soil Mechs. and Fund. Eng. Vol. case hist., Japanese Society of Soil Mechanics and Foundation Engineering, Tokyo, Japan, 611â622.