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PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros
Bearing Capacity Evaluation of Shallow Foundations using the Distinct Element Method
M.C. Weng, S.H. Tung, C.C. Yu and C.I. Ho
Department of Civil and Environmental Engineering, National University of Kaohsiung, Taiwan
M.C. Weng, S.H. Tung, C.C. Yu, C.I. Ho, "Bearing Capacity Evaluation of Shallow Foundations using the Distinct Element Method", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 235, 2009. doi:10.4203/ccp.91.235
Keywords: shallow foundation, distinct element method, granular material.
Traditionally, the bearing capacity of shallow foundations is obtained using the limit equilibrium method suggested by Terzaghi. This theory has some features, such as simplicity combined with reasonable accuracy, that appeals to geotechnical engineers. However, for granular material, such as sand and gravel, its behaviour is significantly influenced by the particle features, which are difficult to model using continuum mechanics. Therefore, the particle-based methods provide an alternative.
This research investigates the bearing capacity of shallow foundations using the distinct element method (DEM). In order to understand the relationship between the properties of the particle bearing capacity, the software PFC2D, based on the DEM, is adopted. In the calculation process, the translational and rotational motion of each element is determined using Newton's second law, while the force-displacement law is used to analyze the contact forces from the relative motion at each contact.
For model generation, a sandbox model of 600 mm width and 300 mm height was analysed. The lateral and lower boundaries were considered as rigid plates, and the upper boundary was unconstrained. A rigid frictional foundation of 42 mm width was put on the cohesionless particles. Then, the compression test was simulated by vertically moving the foundation downward at a constant velocity of 0.1 mm/s. The parameters including the packing of particles, the basic friction angle, the particle size and the particle stiffness are considered to determine the factors of major influence on the bearing capacity.
The simulation results show that: (1) in the dense packing state, the failure pattern is similar to the general shear failure, and in the loose packing state, the pattern reflects the punch failure; (2) an increasing friction angle increase the bearing capacity; (3) the larger size and the higher stiffness will lead to the higher strength, but these major influence factors are not considered in the previous limit equilibrium theory.
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