Seismic Resistance of Breakwater Foundation Reinforced By Steel Sheet Pile and Gabion - Evaluation Through Element Test -

Abstract eng:
Many coastal protection facilities were damaged by the 2011 Off the Pacific Coast of Tohoku Earthquake and the subsequent tsunami, which spread inundation to the coastal plain area. Countermeasures of compound disaster by future mega earthquake such us, Nankai trough earthquake having high probability etc., are issues that should be resolved urgently. The resilient structures that can reduce damage when they are subjected to earthquake and tsunami higher than the design earthquake and tsunami are being developed. A resilient reinforcement technique of breakwater foundation using gabion mound (mound covered with gabion) and steel sheet pile that can minimize damage when the tsunami is higher than the design tsunami height has been developed by Hazarika, et al. (2015). Model tests for evaluating the technique using 1G shaking table has been described in a series paper by Hazarika et al. (2017). In this paper, elements tests were performed for the materials used in foundation materials of the 1G model shaking table test to evaluate the material behavior under cyclic loading. The authors performed monotonic and cyclic triaxial tests for the rubble used as mound material in the model test to evaluate shear deformation properties during static and dynamic loading. Results of this research show that the mound material can mobilize excellent shear resistance under both static and seismic loading condition. The undrained shear strength of the crushed stone used for foundation materials showed a value larger than the gravelly soil and sand of the equal relative density. The cyclic undrained shear strength of the crushed stone showed cyclic mobility during shearing, and also excess pore water pressure ratio Δu/σc' did not reach the perfection liquefaction state defined in 0.95. From the triaxial test results, crushed stone used for mound material was found to have a very large shear resistance. Therefore, it can be inferred that the material contributes to the stability of caisson at all times including under seismic loading.

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