A Critique of b-Values Used for Computing Magnitude Scaling Factors

The objective of this paper is to explore the effects of relative density, effective confining stress, and liquefaction initiation criteria on the slope (or b-value) of the cyclic stress ratio versus number of uniform stress cycles to liquefaction curve in log-log space. The b-value is central to the computation of magnitude scaling factors (MSF) used in evaluating liquefaction potential and can be determined from cyclic laboratory tests such as cyclic triaxial (CTRX), cyclic simple shear (CSS), and cyclic torsional (CTS) tests. This paper provides a summary of b-values calculated from published test data representing multiple types of laboratory tests, sands, sample preparation methods, and liquefaction criteria. Trends between b-values and relative density are shown to be more ambiguous than is often assumed. Effective confining stresses and liquefaction criteria are also shown to have an effect on b-values.