There was a thump and a crash that echoed around the chamber and made the floor heave.

Levelling of generators necessitated by floor heave.

Normally, heaving is not uniform and differentials of up to 12 inches have been reported, although in Canada the maximum measured differential floor heave is about 5 inches.

It is speculated that in the vicinity of the floor fractures, there is more intense floor heave and bedding plane separation and the low of gas is from these.

This paper examines a variety of geotechnical instrumentation and monitoring techniques used to assess strata behaviour during the different phases of longwall mining operations: gateroad deformation, floor heave, intersections, gateside pack behaviour, and subsidence monitoring.