  An experimental technique is presented to quantify the lateral restraint
provided by a geogrid embedded in granular soil at the particle level. Repeated
load triaxial tests were done on transparent sand specimens with geosynthetic
inclusions simulating geogrids. Particle outlines on laser illuminated planes
through the specimens were segmented using a deep learning-based segmentation
algorithm. The particle outlines were characterized in terms of Fourier shape
descriptors and tracked across sequentially captured images. The accuracy of
the particle displacement measurements was validated against Digital Image
Correlation (DIC) measurements. In addition, the method's resolution and
repeatability is presented. Based on the measured particle displacements and
rotations, a state boundary line between probable and improbable particle
motions was identified for each test. The size of the zone of probable motions
could be used to quantify the lateral restraint provided by the inclusions.
Overall, the tests results revealed that the geosynthetic inclusions restricted
both particle displacements and rotations. However, the particle displacements
were found to be restrained more significantly than the rotations. Finally, a
unique relationship was found between the magnitude of the permanent strains of
the specimens and the size of the zone of probable motions.
