A Large Displacement Finite Element Analysis of a Reinforced Unpaved Road (Civil Project)

A series of finite element predictions of the behaviour of a reinforced unpaved road consisting of a layer of fill compacted on top of a clay subgrade with rough, thin reinforcement placed at the interface, is described in this thesis.

These numerical solutions are obtained using a large strain finite element formulation that is based on the displacement method, and are restricted to the case of plane strain, monotonic loading. Separate elements are used to model the soil and reinforcement.

In the finite element formulation, an Eulerian description of deformation is adopted and the Jaumann stress rate is used in the soil constitutive equations. Elastic perfectly-plastic soil model are used which are based on the von Mises yield function for cohesive soil and the Matsuoka criterion for frictional material. Emphasis is placed on obtaining new closed form solutions to parts of calculations that are performed numerically in many existing finite element formulations. The solution algorithm is based on a “Modified Euler Scheme”.

The computer implementation of the formulation is checked against an extensive series of test problems with known closed form solutions. These include the analysis of finite deformation of a single element of material and the calculation of small strain collapse loads. Finite cavity expansion is also studied.

This numerical formulation is used to perform back analyses of a series of reinforced unpaved road model tests. The reinforcement tensions, and the stresses at the interface with the surrounding soil, are calculated using the numerical model and discussed with a view to identifying the mechanisms of reinforcement. Two existing analytical design models of the reinforced unpaved road are described and critically reviewed in the light of the finite element results.
Source: Oxford University
Author: H.J. Burd

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