| 摘要 |
<p>A mine roof support comprises a base formed of two base members, a beam disposed therebetween, jacks for lifting the base members or the beam one relative to the other and a jack for advancing the base member or the beam one relative to the other. A roofing bar structure is supported from the base members by extendible props and an elevated platform is disposed between the base and the roofing bar structure. The support is advanced by lifting, advancing and lowering the beam relative to the base members and then lifting, advancing and lowering the base members relative to the beam.</p> |
