Abstract The paper presents a comparative study between semi-empirical methods for the estimation of pre-consolidation pressure and undrained shear strength from Piezocone (CPTu) data. The first method, proposed by Massad, was developed from observing the variation of these parameters with depth; the second method, proposed by Mayne, was developed from simplifications and relationships between the Spherical Cavity Expansion Theory (SCET) and the Critical State Theory; the third method was proposed by Mayne, which considers the variations due to soil type from the CPT Index to estimate the pre-consolidation pressure. The methods were validated based on their applications to the marine clay from Santos Coastal Plain, Brazil, Bothkennar clay from Scotland, and Torp Clay from Sweden. It is intended to verify if the results are consistent with each other, with the stress history of these soils and with the available test results. The application of the Massad’s method led to results close to the available reference values. The results of the Mayne’s method based on SCET showed great variability in behavior comparing to the test data depending on the case study. By the Mayne’s method based on CPT Index values, the calculated pre-consolidation pressures were slightly higher than the values of the available test data. The variations in the results highlighted the importance of validating estimates based on semi-empirical methods through specific tests and the knowledge of geological history contributes to predicting the behavior of clays, since they showed good agreement with the available data from oedometer tests.

Abstract This paper presents the interpretation of bi-directional load tests performed on three auger piles, in the city of São Paulo, Brazil, using a method based on transfer functions for the shaft and toe. Elastic shortenings of the shaft were directly measured through a displacement indicator at the pile top and two telltales at the upper and bottom plates of the expansive cell. The equivalent top-down load-settlement curves were estimated and compared with two other methods from the literature, one which considers the pile infinitely rigid; and the other, which takes the pile elastic shortening into account. The curves resulted in good agreement considering the pile compressibility. Yet for the infinitely rigid pile, the settlements resulted in up to 75% smaller. Furthermore, the influence of stress relief on the toe behavior due to shaft lifting was investigated. For the cases studied, involving bored and auger piles with the slenderness ratio (Ls/r) greater than 20, the percentage of this effect was generally small, up to 5% of the toe load, being negligible for practical uses.

Abstract The advances in pile monitoring have motivated attempts to support dynamic formulas to estimate pile bearing capacity. Based on numerical analysis of the wave equation and the results of dynamic loading tests in three piles the paper deals with the investigation of the soundness of some of the most used in Brazil, namely, the so called Chellis-Velloso Formula, the Energy Approach Equation and Uto’s Formula. The former gained strength through a misinterpretation of Casagrande (1942) statement that the elastic compression of a pile during driving is a measure of the dynamic force with which the soil is tested, and not of its static resistance. Therefore, the elastic compression and rebound, measured during driving, are generally smaller than the corresponding static values. The second is based on an elasto-plastic load-displacement relationship without physical meaning, besides the fact that the effective energy in driving a pile is related to the work of dynamic forces and has nothing to do with the static resistances. The third was derived from a simplified solution of the wave equation, assuming among other hypothesis that there is no friction along pile shaft. The paper shows the ineffectiveness of attempts to universally validate these formulas with dynamic pile monitoring and the implications in the simulation of static loadings.