Laboratory tests on cyclic undrained behavior of loose sand with cohesionless silt and its application to assessment of seismic performance of subsoil

• This study evaluates the effect of fines on the liquefaction resistance of sands.
• The present study keeps compaction energy constant during torsional shear tests.
• By using the volume compressibility, FC reduces the liquefaction resistance of sand.
• Closed-form solutions were developed to evaluate the seismic performance of a slope.
• The developed solutions are used to determine the required extent of soil improvement.

Geotechnical earthquake engineering in the recent times has been paying special attention to themes such as liquefaction of sand with cohesionless fines, performance-based design, and seismic mitigation measures for housing areas. Because recent earthquakes in Japan and New Zealand caused many liquefaction problems in residential zones, the above-mentioned issues have become even more important than before. The present study conducted laboratory tests on sand with cohesionless fines in order to show how the seismic performance of loose subsoil is assessed, thus developing a practical methodology of performance-based mitigations. Most experimental data obtained is presented together with interpretations, and the mathematical framework for the performance assessment is described together with an example of specified mitigation methods. It is worth mentioning that the target of this assessment is the residential land of people who cannot afford high costs of testing and analysis, therefore, the methodology is simplified as much as possible.