| 摘要 |
A gantry support for supporting a roof of a passage includes two parallel supporting units each having a lower frame provided with articulated tracks and an upper frame carried by props and two cross-members. The two cross-members carry an intermediate upper frame in the form of a beam which is slidable on guide elements and adapted to be clamped to the roof by small jacks. As the support advances the beam remains clamped against the roof of the passage until the beam reaches an end stop. The small jack is then released and the beam slidably advanced along the guide elements by means of a further jack. |
