The longwall panels at Clarence Colliery have experienced intermittent sudden weightings on the face that have caused
some production delays. These weightings have typically been more severe on the wider faces. A program of surface
subsidence and extensometer monitoring was undertaken above Longwalls 4 and 5 to investigate the behaviour of the
overburden strata during longwall extraction on two faces of different widths.
The monitoring indicated that a dome shaped zone of large downward movement extends up into the overburden strata to a
height equal to about the panel width.