R.J. Fannin

Doctor of Philosophy, Magdalen College, Oxford University, Trinity Term 1986

Geogrid Reinforcement of Granular Layers on Soft Clay - A Study at Model and Full Scale


The mechanisms by which a geogrid acts to reinforce a granular layer over a soft clay were investigated with reference to trafficking of unpaved roads. The research involved a programme of physical testing at both model and full scale.

Model tests were carried out for monotonic and cyclic loading of a dual footing on to a layer of granular material that was compacted over a consolidated kaolin sample. The tests were made in conditions of plane strain at a quarter scale, and included a scaled geogrid at the base of the granular layer. Measurements of footing load, displacements and photographic observations through a perspex front face to the test box were used to identify the reinforcing actions of the geogrid.

A virtual work procedure was adopted in analysis of the results for both unreinforced layers. The procedure accounts for lateral restraint of the subgrade and a membrane action in the reinforced tests, and allows a comparison of the cyclic test results with an equivalent monotonic bearing capacity.

Load tests were also made on footing plates at full scale, involving a similar arrangement of compacted granular layers over prepared London clay and including a high strength polymer geogrid. Examination of the test results allowed a qualitative assessment of the model performance and the reinforcing mechanisms attributed to the geogrid.

Thesis (4.85Mb, pdf)

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