Evaluation of Finite Element, Finite Difference and Elasticity Methods for Hypothetical Raft Foundations Installed on Layered Strata
- 178 Downloads
Different numerical methods including 2-D finite element (FE) analysis were implemented for hypothetical raft foundations of high length/breadth ratios to evaluate the reliability of (1) Boussinesq’s method, (2) “rigid-punch” (RP) elastic methods and (3) finite difference (FD) incorporating subgrade reaction theory. A dedicated computer program was developed and used in addition to professional software packages to analyse uniformly loaded rafts of various length/width ratios and stiffnesses, interacting with multi-layered soils of different properties. It was found that the greater the flexibility of the raft the closer was the agreement between the deformations computed from FE and FD methods and the settlements predicted from FE and RP methods. Additionally, the FE method yielded the most realistic predictions principally because of its capability to model and account for the interactions between soil layers as well as the continuity of the soil support. The results revealed that soil stresses computed from elastic methods were inaccurate in cases where a relatively incompressible bedrock existed within depths equivalent to 4 times the raft width or less. This led to a recommendation that in order to predict raft deformations accurately, only those methods that account for both soil-structure and soil–soil interaction should be used in designing raft foundation in practice.
KeywordsRaft foundations Finite elements and finite differences Elastic solutions
Kingston University, the first author’s employer, is thanked for permitting the use of various facilities including computing and laboratory equipment. The University also provided financial support and facilitated valuable discussions between academic staff whose contributions are acknowledged. The second author wishes to thank his dear mother Marzieh, father Azim and brothers Ehsan and Aryan, for their support and patience throughout the programme of work.
- Arbabi A (2011) Finite element modelling of raft foundations on sand overlying clay. Unpublished MSc. Dissertation, Kingston University, UKGoogle Scholar
- ARUP (2011) Oasys safe: geotechnical analysis program. Version 2011. Arup Geotechnics, London, UKGoogle Scholar
- Balunaini U, Damalla Y, Madhav MR (2013) Settlement due to uniform circular load on finite two-layer system. Geotech Geol Eng J, 31:255–265, Springer, DordrechtGoogle Scholar
- Boussinesq J (1885) Application des Potentiels a l'Etude de l'Equilibre et de Mouvement des Solides Elastiques. Gauthier-Villard, ParisGoogle Scholar
- Bowles JE (1996) Foundation analysis and design, 5th edn. McGraw-Hill, New YorkGoogle Scholar
- Das BM (2012) Principles of foundation engineering. 7th Edition, pp 243–262. CENGAGE Learning, 200 First Stamford Place, Suite 400, Stamford CT06902, USA. ISBN-13 978-0495668107Google Scholar
- MATLAB™ (2011) The mathworks IncGoogle Scholar
- Milovic SD (1998) A comparison between observed and calculated large settlements of raft foundations. Can Geotech J 35:251–263, NRC Press, CanadaGoogle Scholar
- Stavridis LT (2009) Rigid foundations resting on an elastic layered soil. Geotech Geol Eng J, 27:407–417, Springer, DordrechtGoogle Scholar
- Tomlinson MJ, Boorman R (2001) Foundation design and construction, 7th edn. Pearson Education Ltd, HarlowGoogle Scholar
- Oasys Safe 19.0 SP4 Build 31 (software), Oasys Ltd (part of the ARUP group) http://www.oasys-software.com