A homogeneous earth dam has a maximum water head difference of $15 \mathrm{~m}$ between the upstream and downstream sides. A flownet was drawn with the number of potential drops as 10 and the average length of the element as $3 \mathrm{~m}$. Specific gravity of the soil is $2.65$. For a factor of safety of $2.0$ against piping failure, void ratio of the soil is $\_\_\_\_\_\_\_\_\_$ (rounded off to $2$ decimal places).