Fig. 9

a Initial (\(t \simeq 0\) s) total stress \(\sigma _{\mathrm{z}}\) versus cliff height H (and H/L) of runs 1–17 in Table 2 (\(L = 13.5\) cm). \(\sigma _{\mathrm{z:front}}\) and \(\sigma _{\mathrm{z:back}}\) indicate the \(\sigma _{\mathrm{z}}\) measured near the cliff toe and the back gate, respectively (see Fig. 2b for these locations). \(\bigtriangleup\) (\(\bigtriangledown\)) indicates the runs in which the rise (fall) in \(\sigma _{\mathrm{z}}\) occurred with seepage. \(\times\) indicates run 9 (see Table 2 legend). A broken (solid) line indicates the lithostatic \(\sigma _0\) [Eq. (5)] calculated for \(\phi = 0.51\) and \(S = 0.14\) (0.55), which is the minimum (maximum) S in Table 2, and separates the super-lithostatic (\(\sigma _{\mathrm{z}} > \sigma _0\)) case above and sub-lithostatic (\(\sigma _{\mathrm{z}} < \sigma _0\)) case below. b \(\sigma _{\mathrm{z:front}}\) at \(t = 0\) s (\(\bigcirc\)) and at \(t = T_\mathrm{seep}\) (\(\diamondsuit\)) versus H. The marker sizes correspond to the \(h_{\mathrm{w}}\). The lithostatic \({\tilde{\sigma }}_0\) after seepage [Eq. (6)] was calculated assuming a parabolic phreatic surface with \(h_{\mathrm{w}} = 2\) cm. The \({\tilde{\sigma }}_0\) increases by only a little (\(\le\) 6%) for \(h_{\mathrm{w}} = 15\) cm