A cylindrical storage bin with an internal diameter of 4 m and a height of 16 m is completely filled with paddy having bulk density of 640 kg·m\(^3\). The angle of internal friction between grain and bin wall is \(30^\circ\) and the ratio of horizontal to vertical pressures is 0.4. When the grain filling rises from 4 m to 16 m in height, the lateral pressure increases by a multiple of \(\underline{\hspace{1cm}}\).