Minimum safe width of 18 m elementary profile

For the elementary profile (right-angled triangle, vertical u/s face, apex at the water level) the minimum width to avoid tension (resultant at the lower third point, $e=B/6$) is

$$B=\frac{H}{\sqrt{S_c-K}}$$

where $K$ is the uplift coefficient ($K=0$ for no uplift, $K=1$ for full uplift at the heel). Here $H=18$ m, $S_c=2.25$.

a) No uplift ($K=0$)

$$B=\frac{18}{\sqrt{2.25}}=\frac{18}{1.5}=12.00\ \text{m}$$

b) Full uplift ($K=1$)

$$B=\frac{18}{\sqrt{2.25-1}}=\frac{18}{\sqrt{1.25}}=16.10\ \text{m}$$

Uplift increases the width needed by about 34%.

Answer: minimum safe width = 12.0 m without uplift and 16.1 m with full uplift. (The friction coefficient is not given, so the sliding width $H/\mu(S_c-K)$ is not checked.)