5:15 PM - 6:30 PM
[SSS11-P01] Elasto-plastic soil-water coupling seismic response analysis of a sedimentary basin with a three-dimensional geometry
Keywords:Sedimentary basin, Seismic response analysis, Elasto-plasticity, Soil-water coupling, Three-dimensional
The seismic wave propagation is strongly affected by the ground non-uniformity. Especially in the sedimentary basin, the amplification in the sedimentary layer, the lens effect, and the edge effect due to the interference of the surface wave generated at the edge of the basin cause the strong ground motion. In this abstract, we conducted a single-phase elastic/two-phase (i.e., soil-water coupled) elasto-plastic seismic response analysis for the three-dimensional spherical basin shown in Table 1(d) and investigated the effects of three-dimensional structures, elasto-plasticity, and the presence of pore water.
First, a single-phase elastic analysis was performed on the three-dimensional mesh (conformed to Miyamoto et al.[1]) shown in Fig. 1. The analysis was conducted with the analysis code GEOASIA[2] developed by the authors. Assuming a plane strain shear box test, the displacement of the front and back surfaces in y-direction was fixed and the periodic boundary was imposed on the left and right surfaces. At the bottom of the model, the vertical displacement was fixed and the viscous boundary condition was imposed in the horizontal direction. The EW component of the Kobe wave shown in Fig. 2 was applied in the x-direction as an input wave. As for the elastic material constants, we considered a clear rigidity contrast (11.4 times in the impedance ratio) between the sedimentary layer and the bedrock. As an analysis result, we confirmed the initial emergence of the ring-shaped strain concentration (Fig. 3), the occurrence of the three-dimensional waves and its long-term retention (Fig. 4).
Next, we compared the three-dimensional result with the reduced-dimensional model shown in Table 1(a)-(c) for evaluating the effect of the three-dimensionality of the sedimentary basin. Figure 5 shows the horizontal response on the ground surface at the center of the basin. As indicated in the figure, all reduced models underestimated the maximum acceleration and the residence time of seismic motion. The result suggests the limitation of the evaluation by the reduced-dimensional model. As for the spectral characteristics, the transfer function of the sedimentary layer at the center of the basin in the three-dimensional case in Fig. 6(d) indicated the amplification in the various frequency range, whereas the one-dimensional calculation in (a) just exhibited the theoretical solution.
Moreover, we conducted the two-phase elasto-plastic analysis. The SYS Cam-clay model [3] was used as the elasto-plastic constitutive equation. The typical parameters for consolidated rock and loose sand were assumed for the bedrock and the sedimentary layer, respectively. The analysis results for 1/10 amplitude of the Kobe wave indicated the decrease of the effective stress (liquefaction) in Fig. 7 and the sloshing behavior of the entire sedimentary layer in Fig. 8. The occurrence of liquefaction could also be confirmed in Fig. 9. Furthermore, the running transfer function in Fig. 10 indicated that the liquefaction reduced the transfer of the shear wave in the sedimentary layer.
(Acknowledgement) Numerical simulations were conducted by utilizing a supercomputer system in Kyoto University, Japan. And we received Grant-in-Aid for Scientific Research (Grant-in-Aid for Scientific Research (A): No. 17H01289).
[1] Miyamoto, T., Irihara, W., Suzuki, T., Fujita, K. and Ichimura, T. (2016): Analysis of strain concentration in alluvium using three dimensional nonlinear seismic ground response analysis (in Japanese), Proc. of JSCE, Vol.72, No.4, I_768-I_776.
[2] Asaoka, A., Noda, T., Yamada, E., Kaneda, K. and Nakano, M. (2002): An elasto-plastic description of two distinct volume change mechanisms of soils, Soils and Foundations, Vol.42, No.5, pp.47-57.
[3] Noda, T., Asaoka, A. and Nakano, M. (2008): Soil-water coupled finite deformation analysis based on a rate-type equation of motion incorporating the SYS Cam-clay model, Soils and Foundations, Vol.48, No.6, pp.771-790.
First, a single-phase elastic analysis was performed on the three-dimensional mesh (conformed to Miyamoto et al.[1]) shown in Fig. 1. The analysis was conducted with the analysis code GEOASIA[2] developed by the authors. Assuming a plane strain shear box test, the displacement of the front and back surfaces in y-direction was fixed and the periodic boundary was imposed on the left and right surfaces. At the bottom of the model, the vertical displacement was fixed and the viscous boundary condition was imposed in the horizontal direction. The EW component of the Kobe wave shown in Fig. 2 was applied in the x-direction as an input wave. As for the elastic material constants, we considered a clear rigidity contrast (11.4 times in the impedance ratio) between the sedimentary layer and the bedrock. As an analysis result, we confirmed the initial emergence of the ring-shaped strain concentration (Fig. 3), the occurrence of the three-dimensional waves and its long-term retention (Fig. 4).
Next, we compared the three-dimensional result with the reduced-dimensional model shown in Table 1(a)-(c) for evaluating the effect of the three-dimensionality of the sedimentary basin. Figure 5 shows the horizontal response on the ground surface at the center of the basin. As indicated in the figure, all reduced models underestimated the maximum acceleration and the residence time of seismic motion. The result suggests the limitation of the evaluation by the reduced-dimensional model. As for the spectral characteristics, the transfer function of the sedimentary layer at the center of the basin in the three-dimensional case in Fig. 6(d) indicated the amplification in the various frequency range, whereas the one-dimensional calculation in (a) just exhibited the theoretical solution.
Moreover, we conducted the two-phase elasto-plastic analysis. The SYS Cam-clay model [3] was used as the elasto-plastic constitutive equation. The typical parameters for consolidated rock and loose sand were assumed for the bedrock and the sedimentary layer, respectively. The analysis results for 1/10 amplitude of the Kobe wave indicated the decrease of the effective stress (liquefaction) in Fig. 7 and the sloshing behavior of the entire sedimentary layer in Fig. 8. The occurrence of liquefaction could also be confirmed in Fig. 9. Furthermore, the running transfer function in Fig. 10 indicated that the liquefaction reduced the transfer of the shear wave in the sedimentary layer.
(Acknowledgement) Numerical simulations were conducted by utilizing a supercomputer system in Kyoto University, Japan. And we received Grant-in-Aid for Scientific Research (Grant-in-Aid for Scientific Research (A): No. 17H01289).
[1] Miyamoto, T., Irihara, W., Suzuki, T., Fujita, K. and Ichimura, T. (2016): Analysis of strain concentration in alluvium using three dimensional nonlinear seismic ground response analysis (in Japanese), Proc. of JSCE, Vol.72, No.4, I_768-I_776.
[2] Asaoka, A., Noda, T., Yamada, E., Kaneda, K. and Nakano, M. (2002): An elasto-plastic description of two distinct volume change mechanisms of soils, Soils and Foundations, Vol.42, No.5, pp.47-57.
[3] Noda, T., Asaoka, A. and Nakano, M. (2008): Soil-water coupled finite deformation analysis based on a rate-type equation of motion incorporating the SYS Cam-clay model, Soils and Foundations, Vol.48, No.6, pp.771-790.