In the current design method of a geogrid-reinforced soil structure, only the tensile strength
(Tult) is taken into account for stability analysis. In fact, the geogrid is also characterised by covering
ratio (CR) (i.e., the ratio of the area covered by geogrid on a plane to the area of that plane). A soil
structure reinforced with the geogrids having the same Tult but different CRs would behave differently.
In the present study, various prototype biaxial geogrids having different CRs were produced by a 3D
printer. The source material was Polyethylene Terephthalate with a Glycol modification (PETG). The
strands were arranged in four different patterns such that four different CR values, i.e., 14%, 25%,
50%, and 100%, were achieved. In so doing, the width of each strand was kept constant, while the
thickness of each strand was varied so that the geogrids with different CR values had similar rupture
tensile strength. A series of triaxial compression tests were performed on uniform air-dried sand
specimens, either unreinforced or reinforced with three or six layers of geogrid having the same CR
value. The followings were found: i) the peak stress ratio (Rpeak) of sand specimens reinforced with
three geogrid layers were controlled by failure of backfill without tensile rupture of reinforcement,
while the Rpeak of sand specimens reinforced with six geogrid layers by tensile rupture of
reinforcement; ii) increasing in the number of geogrid layers increases the Rpeak; and iii) Rpeak generally
increases with an increase in CR until the optimum value, depending on the number of layer, beyond
which Rpeak decreases with an increase in CR. An approximate isotropic perfectly plastic solution was
used to predict the Rpeak. It was found that Rpeak is well predicted if relevant equivalent angle of friction
() is used.