Comparing Methods for Predicting Immediate Settlement of Shallow Foundations on Cohesive Soils Based on Hypothetical and Real Cases


ÖZER M.

ENVIRONMENTAL & ENGINEERING GEOSCIENCE, vol.18, no.4, pp.371-387, 2012 (SCI-Expanded) identifier identifier

Abstract

Many methods are available in literature for the prediction of immediate settlement of shallow foundations resting on cohesive soils. Of these, eight popular methods that are commonly used in practice are summarized briefly and compared using both hypothetical and real cases. In hypothetical cases, various scenarios with respect to the foundation geometry and embedment depth (i.e., different L/B and D-f/B ratios) under fixed loading and soil conditions were considered. Real cases, including all parameters required for the immediate settlement computations, were derived from literature after intensive effort. The results obtained from the comparisons of the hypothetical cases showed that the immediate settlements computed by the methods evaluated in this study are considerably different depending on the ratios of L/B and D-f/B. When the real cases were considered, for the majority of the cases, the best settlement estimates were obtained from the Bowles method. However, for mat foundations, the best settlement estimates were obtained from the Mayne method. In addition, immediate settlement values of foundations founded on multi-layer soil profiles were also compared for both hypothetical and real cases. Two soil layers having different elastic modulus and thickness under fixed loading conditions, embedment depth, and aspect ratio for the foundation were considered in the hypothetical cases. Immediate settlements were calculated by weighted mean, harmonic mean, and principles of superposition in conjunction with the Mayne method, as well as with the full Mayne method with Gibson modulus. Results obtained from the hypothetical cases demonstrated that the immediate settlements calculated by these procedures are remarkably different depending on the variation in the elastic modulus and thickness of the soil layers. For the evaluation of real cases, immediate settlements were calculated by both Mayne and Bowles methods, as well as with the full Mayne method itself. As a result, the full Mayne method with Gibson modulus was determined to produce perfect settlement estimates for real cases compared with the conventional procedures such as weighted mean, harmonic mean, and principles of superposition. In addition, among conventional procedures, principles of superposition in conjunction with the Bowles method provide comparable settlement estimates to the full Mayne method.