REPRODUCTION BY DYNAMIC CENTRIFUGE MODELING FOR E-DEFENSE LARGE-SCALE SOIL STRUCTURE INTERACTION TESTS

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1 Paper No. RDCSA REPRODUCTION BY DYNAMIC CENTRIFUGE MODELING FOR E-DEFENSE LARGE-SCALE SOIL STRUCTURE INTERACTION TESTS Masayoshi SATO 1, Kentaro TABATA 2, Akio ABE 3 ABSTRACT In order to establish experimental procedure to reproduce behavior observed in E-Defense large-scale shake table tests, dynamic centrifuge tests of specimens satisfying a similitude requirement were performed. The E-Defense large-scale tests considered in this study were carried out to investigate dynamic interaction behavior of a soil-pile-structure system in horizontal sand deposit of 8m diameter and 6.3m height prepared in a laminar box. The study also aims to confirm and evaluate the law of similitude by comparing the centrifuge tests with the E-Defense large-scale tests as a prototype. In CASE-1 of the centrifuge tests of a 1:26.7-scale model with sand deposit of 3 mm diameter and 236 mm height, acceleration responses were not sufficiently reproduced in the test due to the large scale ratio of the model. In CASE-2 of a 1:2-scale model with sand deposit of 4 mm diameter and 315 mm height, reproducibility of acceleration responses was improved because of the model larger than that in CASE-1. In contrast, since the shaking table of the centrifuge had no performance to induce necessary displacement, reproducibility of displacement in both CASE-1 and CASE-2 was inadequate. Keywords: Large-scale test,, Reproduction, Soil-pile-structure interaction, Similarity rule INTRODUCTION When experimental research is carried out on soil behavior problems, in many cases it is often necessary to clarify the targeted phenomenon by comparing test results. To carry out such experimental research, it is desirable for the test model size to be as close as possible to the scale of actual situation. However it is difficult to carry out many and varied large-scale tests in terms of cost and duration of the research. Thus, it is efficient to carry out parametric tests on a small-scale, and only especially-important tests on a largescale. From this point of view, centrifuge tests are suitable for carrying out small-scale parametric tests. This is why they are able to satisfy similitude requirements concerning the stress and strain relationship, which is important in research on soil behavior problems. However, at the same time, centrifuge tests have some problems in that they are not able to satisfy similitude requirements regarding soil grain size and strain velocity during shaking of the sand deposit. Furthermore, centrifuge test models are often simplified because they are made by reducing the sizes of the assumed prototype structures by a ratio of from 1/15 to 1/5. Therefore it is important to obtain test results by examining whether centrifuge tests can reproduce seismic behavior of the actual ground and 1 Principal Senior Researcher, National Research Institute for Earth Science and Disaster Prevention, e- mail: m.sato@bosai.go.jp 2 Senior Researcher, National Research Institute for Earth Science and Disaster Prevention, tabata@bosai.go.jp. 3 Head of Tsukuba Laboratory, Tokyo Soil Research Co., Ltd., abe.akio@tokyosoil.co.jp 1

The authors have carried out the following three tests based on the supposition that they represent an actual situation: one on dry sand using a large-scale box [Sato et al.

2 January 211, 1-13 structures. In other words, it is necessary to examine the similarity rule. Nevertheless, it is still the case that the phenomenon regarding seismic soil behavior requires further validation. The authors have carried out the following three tests based on the supposition that they represent an actual situation: one on dry sand using a large-scale box [Sato et al., 1997], one on group-pile foundations in dry sand [Sato et al., 22] and one on group-pile foundations in a liquefiable deposit [Kagawa et al., 24]. The centrifuge test models were made by reducing the sizes of the prototype structures, and tests were carried out to confirm the reproduction performance of such structures. The purpose of this study was to examine whether centrifuge tests are able to satisfy the similitude requirements for large-scale tests. Reproduction tests by centrifuge modeling concerning soil-pilestructure interaction were carried out based on the supposition that tests on a large-scale cylindrical laminar box using the three-dimensional full-scale earthquake testing facility at E-Defense represent an actual situation; both test results were compared regarding the accelerations and displacements of structures and soil deposits and bending strains of the piles. EXPERIMENTAL METHODS Large-Scale Cylindrical Laminar Box Tests using E-Defense Fig. 1 shows a specimen of the [Tabata and Sato, 21]. A laminar cylindrical box was used in the test and had an inside dimension of 8. m in diameter and 6.5 m in height. Fig. 2 shows the large-scale cylindrical laminar box and its outer frame. STRUCTURE (28t) D=154.2mm Dr=7% Fig. 1 Specimen of soil-pile-structure system test using E-Defense. The soil material was silica sand, whose grain size distribution was similar to that of Toyoura Sand as shown in Fig. 3. The soil specimen, which was non-liquefied sand (i.e. dry sand) had a relative density of about 7%. The structure was single lumped mass, which was composed of an upper weight (28. t), and a footing (1. t), while 4 columns supported the weight. The structures consisted of four types, which were; no structure, a high frequency structure with a column length of 1 m, a solid structure with a column length of.3 m and a low frequency structure with seismic isolation rubber, which had a length of.3 m. The group-pile foundation was composed of 9 (3 rows by 3 columns) steel piles, whose outer diameter was 2

January 211, 1-13 Percent finer by mass 1 5 Albany samd Toyoura sand.1.1 1 1 Grain size (mm) Fig. 2 Aspect of a cylindrical laminar box using E-Defense. Fig. 3 Grain-size accumulation curve of soil material.

Piles fixed at the head and pinned at the bottom were applied as the boundary conditions. The shaking table excitation tests were carried out using four types of structure.

4 shows the laminar box that was used in the centrifuge test of CASE-1 [Sato and Tabata, 29].

The models of the structure and group-pile foundation were made by reducing the prototype size followed by the similarity rule shown in Table 1.

be made using steel pipe. The soil material and the production method of the sand deposit were almost the same as that of the s. Fig.

3 January 211, 1-13 Percent finer by mass 1 5 Albany samd Toyoura sand Grain size (mm) Fig. 2 Aspect of a cylindrical laminar box using E-Defense. Fig. 3 Grain-size accumulation curve of soil material. D=152.4 mm, thickness t=2 mm and length l=5.8 m. The distance between each pile was 4D, i.e. 4 times the pile diameter. Piles fixed at the head and pinned at the bottom were applied as the boundary conditions. The shaking table excitation tests were carried out using four types of structure. In order to carry out parametric tests three kinds of seismic wave and three levels of excitation acceleration were applied. Centrifuge Tests of CASE-1 (Scale Ratio: 1/26.7) Fig. 4 shows the laminar box that was used in the centrifuge test of CASE-1 [Sato and Tabata, 29]. It had an inside dimension of 3 mm in diameter and 243 mm in height, and was made by reducing the size of the E-Defense cylindrical laminar box by a scale ratio of 1/26.7. The models of the structure and group-pile foundation were made by reducing the prototype size followed by the similarity rule shown in Table 1. The model piles for the centrifuge tests shown in Table 1 were made using aluminum pipe in order to satisfy the similitude requirement of bending stiffness, because they could not be made using steel pipe. The soil material and the production method of the sand deposit were almost the same as that of the s. Fig. 5 shows the transducer locations of the centrifuge test. Z(+) A-S-Z1 A-S-X A-S-Z2 D-S-X A-G-Z1 X(+) A-F-Z1 A-F-X A-F-Z2 A-G-Z2 A-G-X1 D-F-X A-G-X2 A-G-X3 A-G-X4 236m m 243m m A-G-X5 A-G-X6 A-T-Z1 せん断土槽底板 A-G-X7 A-T-Z2 D-T-X1 3mm Fig. 4 of CASE-1 using cylindrical laminar box (Scale ratio:1/26.7). Fig. 5 Transducer location on centrifuge test of CASE-1 using cylindrical laminar box (Scaleratio:1/26.7). 3

4 Soil Pile Footing Structure Input wave Item 5th International Conference on Earthquake Geotechnical Engineering January 211, 1-13 Table 1. Similitude requirements used in centrifuge test. Symbol Scale ratio At E-Defense, parametric tests were carried out by applying various types of excitation. In the case of this centrifuge modeling the aim was to reproduce two types of excitation; (1) solid structure and NS component of the JR Takatori waves recorded in the Hyogoken-Nambu Earthquake, with maximum acceleration of 81 Gal, shaking in one direction and (2) high frequency structure and NS component of the TAFT wave, with maximum acceleration of 76 Gal, shaking in one direction. Centrifuge Tests of CASE-2 (Scale Ratio: 1/2) Fig. 6 shows that a laminar box was used in the centrifuge test of CASE-2 [Sato and Tabata, 29]. It had an inside dimension of 4 mm in diameter and 357 mm in height. It was made by reducing the size of the E-Defense laminar box by a scale ratio of 1/2. Unit (1/26.7) (1/2) Height H 1/N mm 6, Diameter L 1/N mm 8, 3 4 Density ρt 1 g/cm Length of pile L 1/N mm 5, Diameter D 1/N mm Thickness t 1/N mm Young's modulus E 1 MN/m 2 2.6E+5 7.1E+4 7.1E+4 Area A 1/N 2 m E E E-6 Geometrical moment of inersia I 1/N 4 m E E E-11 Normal stiffness E A 1/N 2 MN 1.95E E E-1 Bending stiffness E I 1/N 4 MNm E-1 1.9E E-6 Thickness D 1/N mm Length L 1/N mm 1, Mass m 1/N 3 kg 1.E E E+ Thickness D 1/N mm 1, Length L 1/N mm 1, Mass m 1/N 3 kg 2.8E E+ 3.52E+ Column length H 1/N mm Natural frequency f N Hz Excitation accleration α N Gal 9 2,43 1,8 Time t 1/N sec Frequency f N Hz Z(+) A-S-Z1 A-S-X A-S-Z2 D-S-X A-G-Z1 X(+) A-F-Z1 A-F-X A-F-Z2 A-G-Z2 A-G-X1 D-F-X A-G-X2 A-G-X3 A-G-X4 315mm 357mm A-G-X5 A-G-X6 A-T-Z1 せん断土槽底板 A-G-X7 A-T-Z2 D-T-X1 4mm Fig. 6 of CASE-2 using cylindrical laminar box (Scale ratio:1/2). Fig. 7 Transducer location on centrifuge test of CASE-2 using cylindrical laminar box (Scale ratio:1/2). 4

5 January 211, 1-13 The model of CASE-2 was made by reducing the prototype size followed by the similarity rule shown in Table 1 which is the same manner of CASE-1. Fig. 7 shows the transducer locations of the centrifuge test. The types of excitation for reproduction by centrifuge modeling were the same as CASE-1. EXPERIMENTAL RESULTS Comparisons of the CASE-1 Centrifuge Tests and Large-Scale Tests at E-Defense A comparison with the centrifuge and results in terms of acceleration responses of the ground surface in the JR Takatori wave and a solid structure test case is shown in Fig. 8 (1), while the acceleration responses of the structure, the footing and the bending strain of the pile are shown in Fig. 8 (2). In Fig. 8 (1), GL stands for a ground level. With respect to the bending strain of the piles was measured at 9 mm below the pile head, those that had been broken or bent during the E-Defense destruction excitation test were selected. Fig. 8 (3) shows a comparison of the displacement of the structure and the table input. Fig. 8 (1) shows a comparison of table input acceleration, revealing that the amplitude in the centrifuge test tends to be larger than that of the large-scale. Therefore, the acceleration amplitudes of GL-5 mm and GL-3 mm in the centrifuge test were larger than that of the E-Defense large-scale test. Based on the comparison, the table input acceleration of the centrifuge test and the large-scale were large different. It is the reasons to be required a table control of high frequency and excitation of large acceleration. The acceleration amplitude of the footing on the centrifuge test was comparatively consistent with that of the E-Defense large-scale test, as shown in Fig. 8 (2). However, the acceleration amplitude of the structure and bending strain of the pile on the centrifuge test was larger than that of the. As shown in Fig. 8 (3), the displacement amplitude of the structure and the table input on the centrifuge test were considerably larger than that of the. The excitation periods of the table displacement especially were very different and the wave forms were entirely different. In Fig. 9 (1) a comparison of the centrifuge test and the in terms of ground acceleration in the case of tests on a high frequency structure, shows the TAFT waves. Similarly the accelerations of the structure and the footing and the bending strain of the pile are shown in Fig. 9 (2), while a comparison of the displacement of the structure, the footing and the table, are shown in Fig. 9 (3). Compared with the acceleration amplitude on GL-5 mm, GL-3 mm and the table input, the input acceleration of the centrifuge test was a little larger than that of the, so that the centrifuge test was larger than that of the in terms of the ground accelerations. The centrifuge test results were not in good agreement with that of the in terms of the acceleration amplitude of the structure and the footing and bending strain of the pile as shown in Fig. 9 (2). However, the amplitude agreements were not bad in comparison with those in Fig. 8 (2). Moreover the centrifuge test results were larger than that of the in terms of the displacement of the structure, the footing and the table input as shown in Fig. 9 (3). The amplitude agreement of the table input in Fig. 9 (3) was better than that in Fig. 8 (3). Overall, the performances to reproduce the by the centrifuge test were not good in CASE- 1, though they were in agreement with some responses concerning the acceleration amplitude. In addition, reproduction performance by the centrifuge test varied with the kind of seismic wave, and the performance using the TAFT wave tended to be better than that using the JR Takatori wave. 5

6 Strain(x1-6 ) 5th International Conference on Earthquake Geotechnical Engineering January 211, (a) Ground acceleration(gl-5mm) (b) Ground acceleration(gl-3mm) (c) Input acceleration(gl-63mm) (1) Responses of acceleration on ground. 8 E-Defence test (b) Footing (c) Bending strain (Depth from pile-head:-9mm) (2) Responses of acceleration on structure, footing and bending strain of pile (b) Input displacement (3) Responses of displacement on structure and table input. Fig. 8 Comparisons of centrifuge test and on response acceleration of CASE-1 (Scale ratio:1/26.7, Solid structure, JR Takatori wave). 6

7 January 211, (a) Ground acceleration (GL-5mm) (b) Ground acceleration (GL-3mm) (c) Input acceleration (GL-63mm) (1) Responses of acceleration on ground (b) Footing (c) Bending strain (Depth from pile-head:-9mm) (2) Responses of acceleration on structure, footing and bending strain of pile Strain(x1-6 ) (b) Footing (c) Input displacement (3) Responses of displacement on structure, footing and table input Fig. 9 Comparisons of centrifuge test and on response acceleration of CASE-1 (Scale ratio:1/26.7, High frequency structure, TAFT wave). 7

8 January 211, 1-13 Comparisons of the CASE-2 Centrifuge Tests and Large-Scale Tests at E-Defense A comparison of the centrifuge and results in terms of ground acceleration in the JR Takatori wave and solid structure test case is shown in Fig. 1 (1), while comparisons in terms of the acceleration of the structure, the footing and the bending strain of the pile are shown in Fig. 1 (2). Comparisons with the displacement of the structure and the table are shown in Fig. 1 (3). Compared with the ground acceleration of GL-5 mm, GL-3 mm and the table in Fig. 1 (1), the centrifuge test results were in agreement with the results in terms of the amplitude and the phase, and the reproduction performance of the centrifuge tests were much improved in comparison with Fig. 8 (1). As shown in Fig. 1 (2), the centrifuge test results were in agreement with the results in terms of the amplitudes and the phases of the acceleration on the structure and the footing and the bending strain of the pile, and the reproduction performance of the centrifuge tests were comparatively good. The centrifuge test results were much larger than that of E-Defense in terms of the structure displacement as shown in Fig. 1 (3). In terms of the amplitude of the table displacement, the E-Defense test result was larger than that of the centrifuge test, so that the agreement was not good. This trend is the same as in Fig. 8 (3). Furthermore, in terms of the period of the table displacement, the centrifuge test was very different from that of the E-Defense as shown in Fig. 8 (3), so that the wave forms were different. Comparisons in terms of ground acceleration response in the test case of a high frequency structure, using the TAFT wave are shown in Fig. 11 (1). Moreover, comparisons with the acceleration on the structure, the footing and of the bending strain of the pile are shown in Fig. 11 (2). Comparisons with the displacement of the structure, the footing and the table input are shown in Fig. 11 (3). Compared with the table acceleration in Fig. 11 (1), the centrifuge and the results were good with regard to the amplitude and the phase. Both test results substantially agreed in terms of the amplitude and the phases of the ground surface accelerations at GL-5 mm and GL-3 mm. In terms of the acceleration of the structure as shown in Fig. 11 (2), the amplitude of the centrifuge test was a little smaller than that of the E- Defense test, while the agreement of both test results was fairly good in the amplitude and the phase, and was also good regarding the footing and the bending strain of the pile. In terms of the displacements of the structure and the footing on the amplitude and the phases, both test results agreed comparatively well, however the amplitude of the footing of the centrifuge test was much bigger than that of the E-Defense test in Fig. 9 (3). Agreement of the table displacement was not good, but the reproduction performance of the centrifuge test was better than that in Fig. 9 (3). The reproduction performance of the centrifuge test using the TAFT wave tends to be better than that of the JR Takatori wave as in CASE-1, because the JR Takatori wave has more low frequency components than the TAFT wave. As a consequence, the performance to reproduce the by the centrifuge test in CASE-2 was improved in comparison with CASE-1, because the scale ratio of CASE-2 with 1/2 is larger than that of CASE-1 with 1/26.7. In consequently, the model of CASE-2 was made more accurately. Note that the difference of the scales between 1/2 and 1/26.7 is distinctive for such scales of the specimens. Specifically, the reproduction performance by the centrifuge test seemed to improve in the case where the model size was larger. However, in both the tests of CASE-1 and CASE-2, the displacement reproduction performance was not good. The main factors were why the maximum displacement stroke of the centrifuge shaker was very small at ±.5 mm and why excitation of 3 Hz or less was impossible. 8

9 Acc. (Gal) Acc. (Gal) Acc. (Gal) Strain(x1-6 ) th International Conference on Earthquake Geotechnical Engineering January 211, 1-13 (a) Ground Acceleration (GL-5mm) (b) Ground Acceleration (GL-3mm) -75 (c) Input acceleration (GL-63mm) (1) Responses of acceleration on ground (b) Footing (c) Bending strain (Depth from pile-head:-9mm) (2) Responses of acceleration on structure, footing and bending strain of pile (b) Input displacement (3) Responses of displacement on structure and table input Fig. 1 Comparisons of centrifuge test and on response acceleration of CASE-2 (Scale ratio:1/2, Solid structure, JR Takatori wave). 9

10 Strain(x1-6 ) th International Conference on Earthquake Geotechnical Engineering January 211, 1-13 (a) Ground acceleration (GL-5mm) (b) Ground acceleration (GL-3mm) -5 (c) Input acceleration (GL-63mm) (1) Responses of acceleration on ground (b) Footing (c) Bending strain (Depth of pile-head:-9mm) (2) Responses of acceleration on structure, footing and bending strain of pile (b) Footing (c) Input displacement (3) Responses of displacement on structure, footing and table input Fig. 11 Comparisons of centrifuge test and on response acceleration of CASE-2 (Scale ratio:1/2, High frequency structure, TAFT wave). 1

11 January 211, 1-13 CONCLUSIONS (1) In order to examine the performance to reproduce the E-Defense large-scale tests by centrifuge tests, they were carried out using a model scale ratio of: 1/26.7 and 1/2, so that data useful for examining the similarity rules could be obtained. (2) For the centrifuge test of CASE-1, a model reduced by a scale ratio of 1/26.7, the sizes of which were 3 mm in diameter and 236 mm in height was made. Though overall some accelerations of the ground could be reproduced, the reproduction results of the structure acceleration varied widely because the model was small. (3) In the centrifuge test of CASE-2, the model was reduced by a scale ratio of 1/2, the sizes of which were 4 mm in diameter and 316 mm in height. Because the size of the model was larger, its accuracy was improved. The reproduction results were improved in comparison with the test of CASE-1. (4) It was found that the larger model improved the accuracy of manufacturing the ground and the structure, and that the reproduction performance was improved. (5) The reproduction performance by the centrifuge test varied according to the kind of seismic waves used as the table input. Tests using the TAFT wave have tended to be reproduced better than those using the JR Takatori wave. (6) In both the tests of CASE-1 and CASE-2, the displacements could not be reproduced well. This is mainly why the capacity of the maximum displacement on the centrifuge shaker used in the reproduction test was small. REFERENCES Kagawa, T., Sato, M., Minowa, C., Abe, A. and Tazoh, T.(24). Centrifuge Simulation of Large-Scale Shaking Table Tests, ASCE, Journal of Geotechnical and Geoenvironmental Engineering, Vol.13, No.7, pp Tabata K. and Sato, M.(21). E-Defense Shaking Table Tests on the Behavior of a Pile-foundation Structure in Full-Scale Model Ground Under Multi-Dimensional Motions, Proceedings of the International Conference on 9th U.S. National and 1th Canadian Conference on Earthquake Engineering, Tronto, Canada, Paper No.1273, p.1. Sato, M., Taji, Y., Ishihara, K., Kagawa, T. and Minowa C.(1997). Large-Scale Laminar Box Tests on Foundation and Buried Structure -No.6 Reproduction of Dynamic Behavior on Dry Sand Deposit by Centrifuge modeling-, Proceedings of the 32th Japan National Conference on Geotechnical Engineering, pp (in Japanese). Sato, M., Minowa, C. and Saito, Y.(22). Reproduction of Large-Scale 1g Test on Dry Sand Deposit and Pile Foundation using Centrifuge Modeling, Proceedings of the International Conference on Physical Modeling in Geotechnics, ICPGM '2, pp Sato, M. and Tabata K.(29). Study on Reproduction Procedure of E-Defense Large-Scale Soil Tests Evaluated by Dynamic Centrifuge Modeling -Tests on Dynamic Soil-Pile-Structure Interaction in Horizontal Sand Deposit-, Report of the National Research Institute for Earth Science and Disaster Prevention, No.76, pp (in Japanese). 11

REPRODUCTION OF A LARGE-SCALE 1G TEST ON UNSATURATED SAND DEPOSITS AND PILE FOUNDATIONS USING CENTRIFUGE MODELING

REPRODUCTION OF A LARGE-SCALE G TEST ON UNSATURATED SAND DEPOSITS AND PILE FOUNDATIONS USING CENTRIFUGE MODELING 293 Masayoshi SATO, Takaaki KAGAWA 2 And Chikahiro MINOWA 3 SUMMARY A dynamic centrifuge