Title page for ETD etd-06082010-020513

Type of Document Master's Thesis
Author Esterhuizen, Jacob J. B.
URN etd-06082010-020513
Title The evaluation of embankment stresses by coupled boundary element - finite element method
Degree Master of Science
Department Civil Engineering
Advisory Committee
Advisor Name Title
Kuppusamy, Thangavelu Committee Chair
Brandon, Thomas L. Committee Member
Duncan, James Michael Committee Member
  • Finite element method
Date of Defense 1993-06-05
Availability restricted

Numerical methods and specifically the finite element method have improved significantly since their introduction in the 60's. These advances were mainly in: 1) introducing higher-order elements, 2) developing effective solution schemes, 3) developing sophisticated means of modeling the constitutive behavior of geotechnical materials, and 4) introducing iteration techniques to model material non-linearity. This thesis, on the other hand, deals with the topic of modeling the boundary conditions of the finite element problem. Typically, the boundary conditions will be approximated by specifying displacement constraints. such as restraining the bottom boundary of the finite element mesh against displacements in the horizontal and vertical directions (x- and y-directions). Where bedrock or dense residual soils underlie the soft foundation soil at a relatively shallow depth, this is a good assumption. However. when soft soil is encountered for large depths, the assumption of zero movement constraints for a mesh boundary at a shallower depth than the actual bedrock will result in a serious underestimation of stresses and displacements. By coupling boundary elements to the finite elements and using them to model the infinite extent of the foundation soil, a more realistic answer is obtained. Employing the coupled boundary element - finite element method, four cases were analyzed and the results compared to values of the pure finite element method. The results show that the coupled method indeed yielded higher stress- and displacement-values, indicating that the pure finite element method underestimates stresses and displacements when modeling very deep soils.

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