Shear Modulus Degradation of a Liquefiable Sand Deposit by Shaking Table Tests
Strength and deformability characteristics of a liquefiable sand deposit including the development of earthquake-induced shear stress and shear strain as well as soil softening via the progressive degradation of shear modulus were studied via shaking table experiments. To do so, a model of a liquefiable sand deposit was constructed and densely instrumented where accelerations, pressures, and displacements at different locations were continuously monitored. Furthermore, the confinement effects on the strength and deformation characteristics of the liquefiable sand deposit due to an external surcharge by placing a heavy concrete slab (i.e. the model of an actual structural rigid pavement) on the ground surface were examined. The results indicate that as the number of seismic-loading cycles increases, the sand deposit softens progressively as large shear strains take place in different sand elements. Liquefaction state is reached after the combined effects of the progressive degradation of the initial shear modulus associated with the continuous decrease in the mean principal stress, and the buildup of the excess of pore pressure takes place in the sand deposit. Finally, the confinement effects given by a concrete slab placed on the surface of the sand deposit resulted in a favorable increasing in the initial shear modulus, an increase in the mean principal stress and a decrease in the softening rate (i.e. the decreasing rate in shear modulus) of the sand, thus making the onset of liquefaction to take place at a later stage. This is, only after the sand deposit having a concrete slab experienced a higher number of seismic loading cycles liquefaction took place, in contrast to an ordinary sand deposit having no concrete slab.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1315545Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 668
 Konagai, K. Kiyota, T. Suyama, S, Asakura, T., Shibuya T., Eto “Maps of soil subsidence for Tokyo bay shore areas liquefied in the March 11th, 2011 off the Pacific Coast of Tohoku Earthquake” Soil Dynamics and Earthquake Engineering, 53 (1):240-253, 2013.
 H. Munoz, F. Tatsuoka, D. Hirakawa, H. Nishikiori, R. Soma, M. Tateyama, K. Watanabe “Dynamic stability of geosynthetic-reinforced soil integral bridge” Geosynthtetics International, 19 (1) 11-38, 2012.
 F. Tatsuoka, H. Munoz, T. Kuroda, H. Nishikiori, R. Soma, T. Kiyota, M. Tateyama, K. Watanabe “Stability of existing bridges improved by structural integration and nailing” Soils and Foundations, 52 (3) (2012), pp. 430-448.
 Zeghal, M. and Elgamal, A-W. “Analysis of site liquefaction using earthquake records”. Journal of Geotechnical Engineering, ASCE, 120, (6): 996-1017, 1994.
 Zeghal, M., Elgamal, A-W., and Tang, H. T. “Lotung downhole array. I: Evaluation of site dynamic properties: evaluation of soil nonlinear properties”. Journal of Geotechnical Engineering, ASCE, 121 (4): 350-362, 1995.
 Zeghal, M., Elgamal, A-W., and Tang, H. T. “Lotung downhole array. II: Evaluation of soil nonlinear properties”. Journal of Geotechnical Engineering, ASCE, 121 (4): 363-378, 1995.
 Brennan, A. J., Thusynthan, N. I. and Madabhushi, P. G “Evaluation of shear modulus and damping in dynamic centrifuge tests”. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 131 (12): 1488-1497, 2005.
 Tatsuoka, F., Iwasaki, T. and Takagi Y. “Hysteretic damping of sands under cyclic loading and its relation to shear modulus”. Soils and Foundations, 18 (2): 25-40, 1978.
 Shibata, T and Solearno, D. S. “Stress-strain characteristics of sand under cyclic loading”. Proc. Japanese Society Civil Engineers, 239 (1): 57-75, 1976.