Fig. 1
From: Experiments on seepage-triggered cliff landslides using cohesive wet sand
a A photo of the sand particles used for the experiments. b A schematic diagram showing the structural change of the wet sand with increasing water saturation S. A box indicates the intermediate S (left: pendular, right: funicular) in which liquid bridges form. c Yield stress \(\tau _{\mathrm{y}}\) versus S (\(\phi = 0.50 \pm 0.02\)) of the wet sand obtained from vane rheometry. A curve is a fourth-order polynomial fit to \(\ln {\tau _{\mathrm{y}}}\) (Takita and Sumita 2013). d Friction coefficient \(\mu\) (\(\bigcirc\): left axis) and cohesion c (\(\times\): right axis) versus S of wet sand obtained from parallel plate rheometry (see Additional file 4: Table S1 for the values of \(\mu\) and c). The \(\mu\) obtained from the angle of repose \(\theta _{\mathrm{r}}\) of dry sand (\(S = 0\)) is also plotted. \(\bigtriangleup\): \(\mu = 0.75\) from a convex pile (Takita and Sumita 2013), \(\bigtriangledown\): \(\mu = 0.80\) from a concave crater (Hayashi and Sumita 2017)