The cohesion $\text{(c)}$, angle of internal friction $\left ( \phi \right )$ and unit weight $\left ( \gamma \right )$ of a soil are $15$ $\text{kPa}$, $20^{\circ}$ and $17.5$ $\text{kN/m}^3$, respectively. The maximum depth of unsupported excavation in the soil (in $\text{m}$, round off to two decimal places) is ______________