Prefabricated metal overcast having a crushable lower section

摘要

A ventilation overcast may comprise a plurality of support columns, each of which has an upper end and a lower end. A plurality of cross beams are connected between the upper ends of each of the plurality of support columns so that the support columns and cross beams define a generally rectangular structure having two opposed side wall portions and a roof portion. A curtain member having a plurality of longitudinal corrugations therein is positioned between the lower ends of adjacent support columns located on the same side wall portion of the ventilation overcast so that a bottom portion of the curtain member contacts the floor of the mine. The longitudinal corrugations allow the curtain member to be crushed when subjected to floor heave.