ABSTRACT
This chapter outlines variations on soil properties from small strain to medium and large strain exhibited during earthquakes. The soil damping ratio cannot be measured in the field as readily as the wave velocities. Soil behaves as an inelastic nonlinear material except for a small strain level. With increasing soil strains during earthquakes, soils change from linear to nonlinear materials. During strong earthquakes, the soil nonlinearity strongly affects the seismic response of soft soil ground and structures on it, and hence the occurrence of structural damage and soil failures such as liquefaction and slope instability. Nonlinear stress-strain relationship not so strongly nonlinear may be approximated by equivalent linearization. In situ wave velocities are the most popular and significant variables to evaluate small-strain soil properties. There are geophysical methods using elastic waves measured by a set of sensors located only at the ground surface, such as, refraction method, reflection method and surface wave method.
