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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 94
Edited by: B.H.V. Topping, J.M. Adam, F.J. Pallarés, R. Bru and M.L. Romero
Paper 139

Numerical Investigation of Scale Effect of Shallow Footings

M. Ornek1, M. Laman2, A. Yildiz3 and A. Demir4

1Civil Engineering Department, Mustafa Kemal University, Iskenderun, Hatay, Turkey
2Civil Engineering Department, Korkut Ata University, Osmaniye, Turkey
3Civil Engineering Department, Cukurova University, Balcali, Adana, Turkey
4Civil Engineering Department, Lousiana State University, Baton Rogue, USA

Full Bibliographic Reference for this paper
M. Ornek, M. Laman, A. Yildiz, A. Demir, "Numerical Investigation of Scale Effect of Shallow Footings", in B.H.V. Topping, J.M. Adam, F.J. Pallarés, R. Bru, M.L. Romero, (Editors), "Proceedings of the Seventh International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 139, 2010. doi:10.4203/ccp.94.139
Keywords: scale effect, clay, sand, footing, bearing capacity factor, footing size.

In geotechnical engineering, most bearing capacity formulations have been derived from model-scale footing tests. It is known from the literature that, small-scale models produces higher values of bearing capacity than that of theoretical equations and therefore they should not be used for the design of full-scale footings without a reduction.

Small-scale model tests are easy to perform and they are less expensive when compared with large and full-scale tests. Because of these advantages, model-scale laboratory tests are more preferable to study the behavior of soil, but it is difficult to simulate soil characteristics (water content, density, strength etc.) exactly, especially in cohesive soils. Despite their operational and financial disadvantages, large and full-scale tests give more reasonable results in simulating soil behavior. The difference in performance between the large or full-scale footing tests and the model footing tests has been addressed by geotechnical engineers in many applications and is known as the "scale effect".

This study is focused on a scale effect investigation in shallow footings resting on clay and sand soils. Plaxis 3D Foundation (finite element code for soil and rock analysis) which is a finite element package especially developed for the analysis of deformation and stability in geotechnical engineering problems was used for the numerical analyses. Three-dimensional analyses were performed with circular, square and strip footings of different sizes. The diameters of the circular footings used in the analyses were 0.5, 1.0, 2.0, 5.0 and 10.0m. The widths of the square footings were varied as 0.5, 1.0, 2.0, 5.0 and 10.0m. The widths of the strip footings were kept constant as 1.0m, the lengths were varied as 5.0, 10.0, 20.0, 50.0 and 100.0m. Mohr Coulomb and hardening soil models were used to simulate clay and sand behaviour, respectively. Before conducting the analyses, the validity of the constitutive models was proved using laboratory and field test results performed by authors.

The results obtained from this study summarized as follows. Numerical analyses, using Mohr-Coulomb Model and hardening soil models gave results that closely match the from physical model tests. The effect of footing size has no clear effect on bearing capacity factor when the footings rested on clay soils. The same behavior was obtained for the circular, square and strip footing shapes. The wedge or self weight bearing capacity factor values decreases with an increase in footing diameter and width in circular and square footings overlying sand soils. In strip footings, the wedge weight bearing capacity factor values increase with an increase in length. The wedge weight bearing capacity factor values were expressed as a function of footing size.

This investigation is considered to have provided a useful basis for further research leading to an increased understanding of the design of footing and bearing capacity problems related to scale effect.

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