High Overburden Stress Effects in Liquefaction Analyses

A reevaluation is presented of two factors that can strongly affect the estimation of liquefaction resistance for clean sands under high effective overburden stresses (σv′): the relation used to normalize penetration resistances to a σv′ of 1 atm (i.e., CN), and the adjustment factor for the effects of σv′ on cyclic resistance ratio (i.e., Kσ). These two factors have been investigated in a number of ways and several relations exist for each of them. An improved CN relation is developed based on cone penetration theory and validation against calibration chamber test data for both cone penetration and standard penetration tests. A relative state parameter index (ξR) is shown to provide a consistent theoretical framework for interrelating the penetration and cyclic loading resistances. It is subsequently shown that the CN and Kσ relations are interrelated through the sand properties and relative density (DR) in ways that have compensating effects on the predicted cyclic resistance. The derived relations provide an improved representation of the effects of high σv′ levels, and reduce the conservatism that results when some established relations are extended to σv′ levels higher than they were calibrated for.