In developing a haulage level in a mine, a horizontal opening with a horseshoe cross$-$section, $4$ m wide and $4$ m high, will be mined parallel to an existing haulage way of the same cross$-$section and on the same horizon. The field principal stresses are $\backslash$sigma v $($vertical$)$ and $0\mathrm{.}5\backslash$sigma v $($horizontal$).$ Ignoring any boundary loosening due to blasting effects, propose a minimum distance between the centerlines of the haulage ways such that, during the development of the second opening, no support problem or local instability is produced in the existing opening. Hint: Approximate the horseshoe openings with circular openings and assume that the first opening will not be impacted if stresses don$$t increase more than $10\%.$