A seepage flow condition is shown in the figure. The saturated unit weight of the soil $\gamma_{\text {sat }}=18$ $\mathrm{kN} / \mathrm{m}^{3} .$ Using unit weight of water, $\gamma_{w}=9.81 \mathrm{kN} / \mathrm{m}^{3},$ the effective vertical stress (expressed in $\mathrm{kN} / \mathrm{m}^{2}$ ) on plane $X-X$ is
A seepage flow condition is shown in the figure. The saturated unit weight of the soil $\gamma_{\text {sat }}=18$ $\mathrm{kN} / \mathrm{m}^{3} .$ Using unit weight of water, $\gamma_{w}=9.81 \mathrm{kN} / \mathrm{m}^{3},$ the effective vertical stress (expressed in $\mathrm{kN} / \mathrm{m}^{2}$ ) on plane $X-X$ is