Pile-soil interaction of laterally loaded piles may be characterized by either linear subgrade modulus methods or the nonlinear loadtransfer relationships, termed p-y curves. The selection of a subgrade modulus to analyze lateral behavior of piles relies heavily on individual judgment because the subgrade modulus itself is a functionof pile deflection. Analyses of laterally loaded piles by means of p-y curves often require extensive numerical procedures on a digitalcomputer. A concept of equivalent subgrade modulus, which incorporates the nonlinear nature of the p-y model, is derived from a parametric study of the effects of pile-soil stiffness under three well-known clay criteria: soft clay and stiff clay above and below the watertable. Design curves of equivalent subgrade modulus versus a dimensionless lateral load factor are developed. A design procedure to predict maximum deflection and maximum moment of laterally loaded pilesin clays is proposed and used to predict published field test data.This paper appears in transportation research record no. 1331, Integrity testing of foundations 1991
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