The successful operation of a longwall face depends significantly on the efficient actions by support systems and on the ability to form a supported beam for a limited time span._x000D_
The mechanical action of the supports can set up complex stresses in the immediate roofstrata._x000D_
The cyclic application of supporting loads to the immediate roofstrata of a longwall face creates a special type of fabric disintegration in the rocks -affected. The mode of application and the distribution of the supporting forces is thus severely modified in a number of cases._x000D_
The occurrence of true fatigue damage in brittle sandstones has been identified by studying the subcritical crack growth and microcrack development in the fracture-tip region. Several mechanical effects peculiar to the cyclic fatigue process have been identified. These effects had not previously been widely recognized. Damage in brittle rocks subjected to cyclic loads is shown to be distinctly different from any other damage processes under either monotonic or sustained (creep) loading conditions._x000D_
The face support systems will frequently support rockmasses with mechanical properties not identified in conventional monotonic or sustained load tests.