Abstract: The present invention relates to a modular system for construction of an overcast for use in a mine. The overcast comprises a plurality of rectangular sheets of cladding each braced to resist out of plane deformation and connected in edge abutment by fastenings extending through holes in edge flanges perpendicular to the sheets. The sheets are supported on each side of being joined to support members comprising two rectangular sheets disposed at an angle one to the other each braced to resist out of plane deformation and each having perforated edge flanges extending perpendicularly along the free edges thereof. The overcast can be extended in either length or span by the addition of further sheets and/or support members. In a modification the support members are fitted with telescopically adjustable legs which can yield in response to floor heave or roof pressure to reduce structural damage to the overcast.

Abstract: A doorway frame for use in underground passageways consists (FIGS. 2, 7) in spaced apart upright members (11,12) the length of each of which may be independently adjusted by an extension member (13,14), a clamp (15) for an adjusted length, and a head member 16 pivotally connected (17) to the upright members (11,12). For preference the doorway frame is provided with a door frame FIGS. (10-12) having removable modular slats (60) extending between upright channel members (51,52) and retained in slots (53) thereof.