Relating K (alpha) & K (sigma) to SPT blow count and to CPT tip resistance for use in evaluating liquefaction potential

The static shear stress ratio correction factor and the overburden stress correction factor have been used as a means for extending field-based liquefaction correlations from level ground conditions to sloping ground conditions and to greater initial vertical effective confining stresses than covered by the empirical data. The recently formulated relative state parameter index was shown to be a practical index for describing the experimentally observed variation of the static shear stress ratio correction factor with both relative density and effective confining stress. The variations of cyclic stress ratio (CSR) with the modified SPT blow count (N
1
)
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or with the normalized CPT tip resistance can also be expressed in terms of this relative state parameter index
E
R
, which then provides a means to estimate the variations of (CSR) with both relative density and effective confining stress, and hence the means to develop expressions relating the overburden stress ratio correction factor to relative density and effective confining stress. This paper describes the subsequent development of relations that can be used to estimate static shear stress ratio correction factor and overburden stress ratio correction factor as functions of both relative density and effective confining pressure. These relationships are also expressed in terms of modified SPT blow count and normalized CPT tip resistance to facilitate their use in practice for estimating the cyclic resistance of soils susceptible to liquefaction during earthquakes. 10 pp., 1 table, 5 figures.