By: Ahmed M. El-Tuhami

Civil Engineering Dept.,

Faculty of Engineering, Al-Azhar University


The present study aims at examining the validity of reinforcing Rammed Aggregate

Piers RAP (which is a technique that has proved to be successful to strengthen soft soil)

with Geogrid shell. This technique depends on providing the soft soil layer with highly

compacted aggregate piers all over the foundation area. However there are different modes

of failure that are associated with this technique including shearing within the reinforced

layer and bulging of the pier. An experimental study has been carried out on a model pier

reinforcing a soft clay layer and statically loaded until failure for unshelled and Geogrid

shelled piers with different shelling lengths. Numerical analyses were conducted using

Plaxis Finite Element code (version 7.2) with Axisymetric modeling techniques. Test results

indicated that shelling of granular piers with Geogrid shell down to a depth of 5 times pier

diameter secures the pier against bulging failure as long as the Geogrid sheet is safe against

tension failure. Shelling of granular piers with a Geogrid shell significantly improves the

bearing capacity of granular piers, hence allowing this technique be used for soft clay

deposits stabilization.

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