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An analysis is presented of a database of 67 tests on 21 clays and silts of undrained shear stress-strain data of fine-grained soils. Normalizations of secant in terms of initial mean effective stress (i.e., versus ) or undrained shear strength (i.e., versus ) are shown to be much less successful in reducing the scatter between different clays than the approach that uses the maximum shear modulus, , a technique still not universally adopted by geotechnical researchers and constitutive modelers. Analysis of semiempirical expressions for is presented and a simple expression that uses only a void-ratio function and a confining-stress function is proposed. This is shown to be superior to a Hardin-style equation, and the void ratio function is demonstrated as an alternative to an overconsolidation ratio (OCR) function. To derive correlations that offer reliable estimates of secant stiffness at any required magnitude of working strain, secant shear modulus is normalized with respect to its small-strain value , and shear strain is normalized with respect to a reference strain at which this stiffness has halved. The data are corrected to two standard strain rates to reduce the discrepancy between data obtained from static and cyclic testing. The reference strain is approximated as a function of the plasticity index. A unique normalized shear modulus reduction curve in the shape of a modified hyperbola is fitted to all the available data up to shear strains of the order of 1%. As a result, good estimates can be made of the modulus reduction across all strain levels in approximately 90% of the cases studied. New design charts are proposed to update the commonly used design curves. [ABSTRACT FROM AUTHOR]

The response of a laterally loaded pile is normally dominated by the limiting force per unit length profile (LFP, ) mobilized along the pile to the depth of the plastic zone (e.g., maximum slip depth, max ) and depends on pile-soil relative rigidity (via the subgrade modulus of elasticity ). The values of and the shear modulus (, thus ) were deduced extensively against the measured response of 32 and 20 piles tested in situ in clay and sand, respectively. In this paper, simplified closed-form solutions are presented for the design of laterally loaded piles. The parameters of the and the obtained previously are utilized to examine the impact of loading eccentricity on piles and to assess the validity of existing -profiles. Expressions are also explored and provided regarding determinations of the -profiles, the modulus of the subgrade reaction (via ), the ranges of the plastic zone (max ), and the depth of elastic influence (via the critical pile length ), along with the correlations between the shear modulus of soil and undrained shear strength () and/or the standard penetration test blow count (). It is noted that the popularly adopted LFPs (such as Matlock's LFP, Reese's LFP, and American Petroleum Institute code methods) are not sufficiently accurate for 60-85% of the 52 piles investigated herein, especially for those with a diameter >1.5 m. [ABSTRACT FROM AUTHOR]