Recent findings about the confining effect of geogrids from large scale laboratory testing

To investigate the contribution of geogrids to the strength of reinforced soil large scale labora- tory triaxial and plane strain testing has been carried out at RWTH Aachen University. The outcomes of the triaxial tests clearly show the development of an additional confining effect of the reinforcement. The contri- bution of this effect to the development of the horizontal earth pressure on the facing of reinforced retaining walls has then been investigated with plane strain model tests. The significant reduction of the earth pressure, that has been assumed and reported various times during the past two decades, could be confirmed with these tests. However, analysing displacements and rotations of the soil particles during retraction of the facing, the deve- lopment of shear zones within the reinforced soil body has been identified. The results clearly show an arch- ing effect of the soil between the stabilizing geogrid layers.