Abstract: The invention provides a bag for spacing apart walls in an underground mine working, and including opposed load-bearing walls of flexible sheet material, each defining a substantially centrally located opening and an open-ended radial slot extending between and intersecting the central opening and outer periphery of the load-bearing wall, the openings and slots of the load-bearing walls being in register. There is an intermediate wall of flexible sheet material extending between the load-bearing walls and connected thereto substantially along the entire periphery of each load-bearing wall. A charging connector through the wall is for connection to a source of flowable substance under pressure for charging the bag therewith, to expand the bag by displacing the load-bearing walls away from each other. The invention also provides an installation and method which employ the bag to space the walls apart.