A review of partial saturation in liquefaction assessment: theory, laboratory studies, and field case histories

Liquefaction triggering analyses commonly assume that soils below the groundwater table (GWT) are fully saturated. In loose, granular soil deposits, this assumption suggests an increased potential for liquefaction. However, soil deposits below the GWT may be only partially saturated due to the presence of entrapped air in the pore water, which can significantly alter liquefaction resistance. Laboratory studies have shown that liquefaction resistance increases as the degree of saturation (S r ) decreases. P-wave velocity (V P ) is a reliable parameter for assessing saturation conditions in both laboratory and field settings. In fully saturated soils, compression waves propagate at velocities comparable to that of water, (~ 1500 m/s), whereas V P values below this threshold indicate partial saturation. Laboratory results show a strong, nearly exponential empirical relationship between V P and liquefaction resistance, with resistance increasing significantly as V P decreases. This relationship enables the development of partial saturation correction factors that can be applied to the factor of safety against liquefaction triggering, thereby improving prediction accuracy by accounting for the additional liquefaction resistance associated with partial saturation. This paper provides researchers and practitioners with a consolidated basis for understanding and accounting for partial saturation in liquefaction assessment, progressing from its theoretical and experimental basis to field identification and application. The review consolidates findings dispersed across individual studies and provides a new synthesis of field case histories within a common framework, enabling consistent comparison and a unified interpretation of the influence of partial saturation on liquefaction response. The findings highlight how accounting for partial saturation can support more representative liquefaction hazard and risk assessment.