What is the cyclic stress ratio used for in relation to soils?

The cyclic stress ratio is a critical parameter used in geotechnical engineering, particularly in assessing the liquefaction potential of soils, especially sandy soils during seismic events. It represents the ratio of the cyclic shear stress induced in the soil to the effective overburden stress. When subjected to repeated loading, such as that caused by an earthquake, certain soil types can lose their strength and behave like a liquid; this phenomenon is known as liquefaction.

In sands, the cyclic stress ratio helps engineers to evaluate how susceptible a soil deposit is to liquefaction under cyclic loading conditions. By understanding the cyclic stress ratio, engineers can make informed decisions regarding site safety and necessary mitigative measures, such as ground improvement techniques.

The other options do not fit the function of the cyclic stress ratio. For example, measures of thermal properties relate to different aspects of soil behavior under thermal changes, while a rating of shear resistance in cohesive soils pertains to undrained conditions rather than cyclic loading. Lastly, calculations for soil porosity focus on the void space within the soil matrix, which is unrelated to the cyclic behavior and potential for liquefaction. Hence, the correct answer highlights the specific role of the cyclic stress ratio in assessing liquefaction potential in sandy soils.