A vertical trench is excavated in a clayey soil deposit having a surcharge load of $30 \mathrm{~kPa}$. A fluid of unit weight $12 \mathrm{~kN} / \mathrm{m}^3$ is poured in the trench to prevent collapse as the excavation proceeds. Assume that the fluid is not seeping through the soil deposit. If the undrained cohesion of the clay deposit is $20 \mathrm{~kPa}$ and saturated unit weight is $18 \mathrm{~kN} / \mathrm{m}^3$, what is the maximum depth of unsupported excavation (in $\mathrm{m}$, rounded off to two decimal places)?________________