For the dual-wheel carrying assembly shown in the figure, \( P \) is the load on each wheel, \( a \) is the radius of the contact area of the wheel, \( s \) is the spacing between the wheels, and \( d \) is the clear distance between the wheels. Assuming that the ground is an elastic, homogeneous, and isotropic half space, the ratio of Equivalent Single Wheel Load (ESWL) at depth \( z = \frac{d}{2} \) to the ESWL at depth \( z = 2s \) is \(\underline{\hspace{1cm}}\) (round off to one decimal place).
