Geogrid reinforced soil is an advanced composite material that is widely used for the construction
of retaining walls as frequently needed in transportation structures. Most standards
and proposed design methods have included a beneficial effect of geogrid
reinforcement on the earth pressure that acts on the facing of a retaining wall. However,
field measurements at applications often show much lower deformations and stresses as
estimated from the design. This indicates a certain improvement potential for the design
of geogrid reinforced soil structures and thereby for the general acceptance of geogrid reinforced
soil. Therefore, at RWTH Aachen University model tests with geogrid reinforced soil
retaining walls have been carried out. The design of the developed test apparatus allows
the determination of various parameters, such as the determination of the earth pressure
distribution at the facing, geogrid connection loads at the facing and specimen deformations
throughout the whole cross section of the test wall.
This article deals with the results of parametric studies focusing on the reduction of the
active earth pressure in geogrid reinforced retaining structures due to geogrids with
varying reinforcement ratio, i.e. number of reinforcement layers per specimen height,
and reinforcement stiffness. A reduction of the earth pressure due to a surface load was
apparent already underneath the topmost reinforcement layer. This effect was observed
for both, structures with and without a facing connection of the reinforcement. With
increasing reinforcement ratio, the sliding soil wedges decreased in size and only an
unconfined soil area, beneath a developing soil arch in between two reinforcement layers,
caused a horizontal earth pressure on the facing. All observations were merged to formulate
a mechanical model idea that is presented at the end of this article.